Temperature overshoot and tipping points

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Key points:

  • Under the Paris Agreement, countries committed to limiting global temperature increase to 1.5°C or ‘well below’ 2°C above pre-industrial levels. However, even in an optimistic emissions scenario, the chance of limiting warming to 1.5°C by the end of the century is now virtually zero.
  • Our journey to achieving Paris Agreement goals will likely entail ‘temperature overshoot’, where warming exceeds a specified level (typically 1.5°C to 2°C) for 10 years or more before returning to that level in the future. 
  • Ninety percent of the mitigation pathways in the IPCC’s Global Warming of 1.5°C report that limit warming to 1.5°C by 2100 include temperature overshoot.
  • Pathways that limit warming to 1.5°C with limited or no overshoot require deep, rapid, and sustained reductions in emissions, as well as some carbon dioxide removal to compensate for sectors that cannot be decarbonised.
  • Even temporary overshoot increases the risk of Earth systems reaching ‘climate tipping points’, catalysing large and often irreversible changes. For example, deforestation in the Amazon could trigger a deforestation-drought feedback loop, rapidly transforming the region into a savanna.
  • Every increment of avoided warming can make a difference. Keeping overshoot as short and at as low a temperature as possible is critical to avoid sudden, cascading and irreversible climate impacts.
  • Without rapid emissions cuts now, we will need to rely more heavily on large-scale carbon dioxide removal to bring temperatures back down after overshoot, which comes with risks and uncertainties. 
  • Other proposed large-scale climate interventions, known as geoengineering, fail to address the root causes of climate change and introduce additional severe risks. 
  • Strategically targeting ‘positive socio-economic tipping points’ – which are conditions that accelerate the deployment of technologies or practices to reach net zero – could help drive decarbonisation and allow us to meet the 1.5°C target.

Surpassing the Paris Agreement limits

Last year, the Earth’s average temperature reached around 1.5°C warmer than pre-industrial times. The average warming for the decade between 2015 and 2024 was 1.24°C above pre-industrial times. The heating is predominantly a result of human activities1Human-cased warming is estimated to have caused 1.36°C of warming in 2024, relative to 1850–1900., primarily the burning of fossil fuels. This warming has had widespread adverse impacts on people and nature, which will worsen as the climate continues to warm. 

The Paris Agreement was adopted at COP21 in 2015 by most countries worldwide – countries that are collectively responsible for 98% of human-caused emissions – with the primary goal of avoiding the most devastating impacts of climate change. The agreement aimed to limit “the increase in the global average temperature to well below 2°C above pre-industrial levels” and to pursue efforts “to limit the temperature increase to 1.5°C above pre-industrial levels” by the end of the century. The US, currently responsible for 13% of global emissions, announced its withdrawal from the Agreement in January 2025.

It is now clear that achieving the Paris Agreement goals will mean stricter measures to reduce emissions. Net carbon dioxide emissions will need to fall by 48% by 2030 to keep warming to 1.5°C, according to the latest IPCC assessment, published in 2022. More recent estimates suggest emissions would need to fall >around 50% over the same timeline. The 2024 Emissions Gap Report finds that, even under an optimistic scenario where all NDCs and net zero pledges are met, the chance of limiting warming to 1.5°C by the end of the century is “virtually zero”. The 2023 Emissions Gap Report gave a 14% chance, as, at the time, there were more opportunities to scale down emissions. 

Countries had agreed to submit more ambitious national climate plans by 2025 as part of the Paris Agreement. However, as of October 2025, countries have only pledged to reduce their emissions by 1.6 billion tonnes more than in their previous NDCs, leaving a gap of 26.5 billion tonnes to stay within the 1.5°C limit.

The latest stocktake of the global carbon budget – the amount of carbon that can be emitted before we reach 1.5°C of warming – estimates that we will burn through the remaining carbon budget in about six years. Other estimates suggest that we may have only three years left to reduce emissions sufficiently to limit warming to 1.5°C, and that for a 50% chance of keeping warming to 1.5°C, greenhouse gas emissions would have needed to peak before 2025. Yet, emissions continue to rise and national commitments to reducing emissions remain insufficient. 

Every fraction of a degree of warming increases the odds of additional, and often extreme, impacts. As greenhouse gases build up in the atmosphere, heatwaves are becoming hotter and more frequent and rainfall is becoming more intense and variable. Consequently, droughts and floods are worsening globally, triggering crop failure, infrastructure damage and humanitarian crises.

As emissions continue to rise, it is increasingly likely that our journey to limiting warming will entail a period of ‘temperature overshoot’. Unprecedented efforts are needed, soon, to limit the amount of overshoot and the impacts of temperature rise. 

What is temperature overshoot?

Temperature overshoot is the term used by the Intergovernmental Panel on Climate Change (IPCC) to describe scenarios, or ‘pathways’, in which the Earth exceeds a specified global warming level, typically between 1.5 and 2°C, before returning to that level at some point in the future. 

The magnitude (how much the specified level is exceeded) and the duration (how long it is exceeded for) differ across pathways. In most overshoot pathways, the duration of the overshoot is at least one decade and can extend to several decades, while the magnitude reaches up to 0.5°C. However, in ‘high overshoot’ pathways where the temperature overshoots by as much as 0.5°C, it is unlikely that warming could be returned to ‘well below 2°C’ by 2100. If we follow these high-overshoot pathways, we will not meet the goals of the Paris Agreement.

Most IPCC scenarios foresee some degree of temperature overshoot

Pathways with temperature overshoot are not exceptional. In the IPCC’s Global Warming of 1.5°C report, published in October 2018, 90% of the mitigation pathways that limit warming to 1.5°C by 2100 include a period of overshoot. 
The pathways that limit warming to 1.5°C with limited or no overshoot require deep, rapid and immediate reductions in emissions, with carbon dioxide removal (CDR) only used to compensate for historical emissions and in sectors where no mitigation measures are available.‘2Limited-overshoot’ pathways overshoot 1.5°C by no more than 0.1°C. In comparison, pathways that delay emissions cuts and overshoot the temperature targets rely more heavily on large-scale CDR to bring global temperatures back down by the end of the century.

Explaining 1.5°C scenarios with and without overshoot

Figure 1 illustrates three hypothetical overshoot scenarios for pathways that aim to achieve the 1.5 °C target. In the upper panel, the grey line represents a scenario with no temperature overshoot. The blue line represents a scenario with a low magnitude and short duration of overshoot. The red line represents a scenario with a high magnitude of temperature overshoot that persists for a long time. In the blue and red scenarios, temperatures return to 1.5°C by the end of the century

The lower panel shows emissions trends in each of the pathways. The scenario represented by the grey line reaches net-zero emissions, at which point temperatures stabilise at 1.5°C, by rapidly reducing emissions and without the need for negative emissions solutions. In contrast, the scenarios represented by the blue and red lines require negative emissions solutions, such as large-scale CDR, to reach net-zero emissions. In the red scenario of high and long-lasting overshoot, negative emissions solutions will need to be deployed far beyond the end of the century. 

The greater and longer the overshoot, the more negative emissions solutions will be needed in order to stabilise temperatures at 1.5°C.

Figure 1: Illustration of 1.5°C scenarios with and without overshoot

Source: Reversing climate overshoot, Nature Geoscience 16, 467 (2023).

Increasing overshoot means increasing climate impacts

Every increase in the magnitude and duration of overshoot increases the severity, frequency and duration of climate impacts, such as heatwaves, droughts and floods. In one analysis, the frequency of agricultural drought increases from 24% in a 1.5°C scenario with little to no overshoot to 31% in an overshoot scenario that reaches just below 2°C by the end of the century. In the same scenarios, the frequency of major heatwaves increases from 29% to 44%. Brazil, North Africa, and southern Africa are projected to be the most severely impacted by heatwaves exacerbated by temperature overshoot. 

Sticking to the 1.5°C target also brings economic benefits – climate impacts from temperature overshoot will lead to higher mitigation costs and economic losses later in the century.3While higher initial investments are needed to keep temperatures down, this is outweighed by the economic benefits later in the century. 

For nature, exceeding a temperature threshold for even a short amount of time may push species beyond their tolerance limits, causing extinction, migration and knock-on effects for entire ecosystems. As different parts of the world warm and cool at different rates, species worldwide will be unevenly exposed to dangerous conditions. Temperature overshoot will be particularly critical for species already living close to their thermal limits, such as those in the tropics.

The IPCC estimates that the area of global land at risk of changing from one ecosystem type to another – such as a forest changing to a grassland – is 50% lower at 1.5°C of warming compared to 2°C. Some of the world’s most important ecosystems, such as the Amazon Basin, the Pantanal and the Coral Triangle, could be irreversibly transformed with just a few years of overshoot. 

In the ocean, overshoot is projected to decrease ecosystem habitability for centuries to come. If we do not curtail emissions now, marine ecosystems in the Indo-Pacific, Caribbean and West Africa could experience sudden collapse as early as the 2030s, with knock-on effects for the people who rely on these ecosystems for food and income from tourism. 

Every increment of warming counts

2025 has been hot. It is on track to be the second or third warmest year on record. It is also likely to be the second year since pre-industrial times where the average global temperature exceeded 1.5°C. This occurred for the first time in 2024, which was recorded as the warmest year on record since pre-industrial times and broke multiple heat records on land and in the sea. Although a breach of the Paris Agreement target would require average annual temperatures to be above 1.5°C for at least 20 consecutive years, the fact that we are increasingly seeing individual years surpass this threshold implies that we are getting closer. 

A ‘safe’ limit to global warming does not exist, and we are already seeing devastating impacts at current warming levels. IPCC scientists urge that 1.5°C shouldn’t be viewed as a guardrail. The target of 1.5°C was chosen as a threshold beyond which the impacts of warming become increasingly intolerable to humans and nature. This assessment was made based on criteria such as food security, extreme weather events, health, biodiversity loss, water supply and economic growth. 

But, what is considered an acceptable level of damage from global warming is highly subjective. At just 0.56°C of warming, 506 people died from climate change-induced heat stress in Paris during the summer of 2003. At 0.95°C of warming, wildfires in Australia in 2019-2020 led to the death or displacement of three billion wild animals and caused AUD 4-5 billion in losses to the Australian food system.     

While we have not permanently surpassed the 1.5°C target, we are already experiencing significant impacts of global warming. In 2024, climate change was responsible for an additional 41 days of dangerous heat, and extreme weather events worsened by climate change resulted in the death of thousands of people and billions in damages. These represent only a tiny fraction of all impacts resulting from human-caused warming.

We should do everything in our power to keep warming down as much as possible. As emphasised by IPCC scientist Prof. Mark Howden in 2018: “Every half a degree matters. Every year matters. Every choice matters.”

What are climate tipping points?

Overshooting temperature targets, even temporarily, risks the creation of positive feedback loops – self-perpetuating cycles that speed up warming. These positive feedback loops can trigger climate ‘tipping points’, after which an Earth system transforms into an alternative stable state, completely different to its original state. A single tipping point can have cascading and catastrophic effects at regional and global scales. 

For example, the Amazon is drying and burning due to human-caused warming, which reduces tree cover. Reduced tree cover, exacerbated by deforestation, causes further reductions in rainfall due to decreased evapotranspiration, whereby moisture is evaporated into the atmosphere from trees. Over time, this deforestation-drought feedback loop could pass a tipping point, transforming the region from a rainforest into a savanna. This would switch it from one of the most important global carbon sinks to a carbon source and could trigger potentially catastrophic changes to global rainfall patterns, impacting agriculture.  

The transformation of the Amazon is a fast-onset tipping point, in that when the tipping point is transgressed, the change in the climate system would occur rapidly – in a matter of decades. For these tipping points, overshoot could cause sudden and irreversible changes to the system. Scientists are uncertain when the Amazon’s tipping point might be crossed. Some estimates suggest this could happen at 40% forest loss, and around 26% of the Amazon was already deforested or degraded as of 2022. Some scientists believe that the first warning signals of this shift are already here. 

Other tipping points are slow-onset tipping points, whereby the change to an Earth system occurs over a much longer timescale, like over many centuries. For these tipping points, briefly overshooting temperature targets might not cause immediate and irreversible changes to the climate system, as long as the overshoot is not longer than the time needed for the system to recover. One example is the melting of the Greenland ice sheet. While we may be close to this tipping point, it is estimated that ice sheet loss could be mitigated as long as temperatures are brought back down to 1.5°C or lower relatively quickly once the tipping point is reached.Even temporary overshoot increases the risks of surpassing critical tipping points by 72% compared to scenarios with no overshoot. Keeping the magnitude and duration of overshoot as low as possible is critical and rapid decarbonisation is key: While delaying emissions reductions to beyond 2030 could still allow us to meet 1.5 °C by the end of the century, this would result in higher temperature overshoot over many decades, with the potential for adverse consequences.

Boundaries for keeping the Earth habitable

Humans have altered the Earth, such as by depleting the ozone layer, reducing biodiversity, changing land cover and warming the atmosphere. Scientists have tried to estimate how far these processes could continue to be altered until a global tipping point is reached, causing the Earth to transform irreversibly into a state that could endanger humanity and render the planet uninhabitable.

Planetary system boundaries

The concept of planetary system boundaries involves tracking changes to nine crucial processes, identified by scientists as responsible for keeping the Earth habitable (Figure 2). These processes are ranked on a scale from ‘safe operating’, meaning the process happens in a way that is safe for humanity, to ‘high-risk’, i.e. the process poses a high risk to humanity.Of the nine identified planetary boundaries, the Earth is now outside the safe zone for seven: Climate change, biosphere integrity (the quality of living organisms and ecosystems, impacted by, for example, decreasing species diversity), land-use change, biogeochemical flows (for example of nitrogen and phosphorous – aggravated by agribusiness and industry), novel entities (the release of novel chemicals such as plastics), freshwater change and ocean acidification. The safe space for ocean acidification was added as breached in September 2025, reflecting worsening trends.   

Figure 2: Planetary system boundaries 

Source: Seven of nine planetary boundaries now breached – ocean acidification joins the danger zone, Potsdam Institute for Climate Impact Research (2025)

There is great scientific uncertainty regarding how much longer we can continue to push these boundaries before the total collapse of the Earth’s system happens. However, if we rapidly decarbonise, we could reduce this risk and stabilise the Earth within a safe operating space. 

Earth system boundaries

Scientists have also proposed a set of ‘safe and just’ Earth system boundaries that quantify the safety of humans and the stability of the planet (Figure 3). Safe boundaries are those “where biophysical stability of the Earth system is maintained and enhanced over time, thereby safeguarding its functions and ability to support humans and all other living organisms”. Just system boundaries minimise the exposure of countries, communities and people to significant harm, including “loss of lives, livelihoods or incomes; displacement; loss of food, water or nutritional security; and chronic disease, injury or malnutrition”. 

This framework differs from previous frameworks in that the impacts on people are measured in comparable units to impacts on the planet. While other frameworks only assess how human activities have impacted Earth systems, using comparable units allows for a better understanding of the harm that changes to Earth system boundaries will do to humans. The framework focuses on all species, not just humans, attempting to “define the environmental conditions needed not only for the planet to remain stable, but to enable societies, economies and ecosystems across the globe to thrive”. The framework also incorporates information on climate, the biosphere, and other Earth system tipping points into the Earth system boundaries

Figure 3: Safe and just Earth system boundaries

Source: Safe and Just Earth System Boundaries published in Nature, Global Commons Alliance (2023).  

According to this framework, the ‘just’ Earth system boundary for climate is 1°C, while the ‘safe’ boundary is 1.5 °C. The Earth has already heated by more than 1.2 °C, meaning current global warming, while still in the ‘safe’ zone, is unjust (Figure 3), emphasising the need for urgent action. As the framework incorporates interspecies justice, intergenerational justice and intragenerational justice (including race, class and gender), it can be used to inform sustainability targets and practices. 

However, these frameworks have been criticised, with some suggesting that they are too simplistic or that they do not distinguish between thresholds, that can be breached, and hard limits, that cannot be breached. They may also shift political focus to the wrong areas or dampen political action. Others warn against allowing one group of scientists to define what constitutes a safe set of boundaries for everyone on the planet, which could be viewed as divisive. 

Relying on carbon removal is risky – emissions cuts must come first

To bring average global temperatures back down to between 1.5 and 2°C, overshoot scenarios rely to different extents on CDR. This includes nature-based solutions, such as afforestation (planting forests) and bioenergy with carbon capture and storage (BECCS). Other solutions include direct air capture (DAC) and storage, where CO2 is directly captured from the air and then stored for the long term. 

However, there are major risks and uncertainties with these approaches. With nature-based CDR and BECCS, there is a risk that ecosystems could be replaced with bioenergy crops or plantations, endangering wild plants and animals. Food crops could be supplanted, threatening food security. DAC technology is still in its infancy. These technologies are also not proven to be effective at the scale needed. 

These uncertainties and risks emphasise that climate action needs to be boosted in the near-term to reduce our reliance on these approaches for bringing temperatures back down later in the century. 

Geoengineering cannot replace rapid and deep emissions cuts

Rapid and deep emissions cuts provide the best chances of limiting temperature overshoot and avoiding tipping points. At the same time, approaches that remove carbon from the atmosphere can help to offset emissions that cannot be reduced and mitigate overshoot. 

Technologies that aim to intervene with Earth systems at a large scale to counteract the effects of a warming climate, referred to as geoengineering, have also been increasingly proposed in recent years.4CDR is also defined as a geoengineering approach by the IPCC. A prominent solution is solar radiation management (SRM), which aims to reduce the amount of sunlight absorbed by the Earth by reflecting it back into space or preventing it from reaching the Earth’s surface altogether. This would result in reduced warming, but would have no impact on greenhouse gases that are being released into the atmosphere or that are already there, meaning it does not tackle the underlying causes of climate change and instead introduces new and additional risks. 

Research remains in early and theoretical stages, with many unknowns and potential unintended consequences. Studies suggest that SRM would have significant impacts on water cycles, could modify monsoon systems, and could lead to drought in some tropical regions. SRM could also impact renewable energy generation, which is crucial for mitigating emissions. Additionally, as its deployment would impact the climate of the entire planet, SRM comes with substantial geopolitical risks. 

SRM approaches would have to be implemented continuously until emissions are reduced to safe levels to prevent warming. If they are stopped before this happens, this would result in very rapid warming, and “severely stress ecosystem and human adaptation”, according to the IPCC. The IPCC is very clear that, even in best-case scenarios, SRM is a supplement to rapid and deep emissions cuts. 

Positive tipping points can help us reach net zero

In contrast to climate tipping points, positive tipping points – otherwise known as positive socio-economic tipping points – occur when a set of conditions is reached that can accelerate the deployment of technologies or practices to achieve net zero. For instance, a new technology begins to outcompete an old technology. Sales of the new technology facilitate further development, which in turn reduces its costs, allowing the new technology to become widespread and replace the old. An example of this is the rapid development of renewable energy, where over just 10 years, solar and wind technologies have become the cheapest source of power in many parts of the world.   

Targeted interventions in socioeconomic, technological and political systems can be used to advance climate change mitigation, and strategic investment can help bring down the costs of technologies that facilitate decarbonisation. For example, oil and gas companies have been accused of having overly optimistic projections of long-term oil prices, resulting in an inflated picture of future economic performance. Updating the accounting standards or disclosure guidelines for these companies could cause prices to decrease, thereby curbing investment and catalysing investment into renewables. 

The focus on these positive tipping points should not distract us from the need to rapidly decrease emissions. Rather, these positive tipping points should be viewed in the context of driving strategic interventions to encourage decarbonisation.

This briefing was originally published in December 2023. This updated version was published in October 2025.

Net-zero progress overblown by inconsistencies in land carbon accounting

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Key points:

  • Nationally Determined Contributions (NDCs) – which outline national governments’ commitments to emissions reduction – account for land-based carbon removal using different methods to the IPCC. 
  • When the methods are harmonised, NDCs reduce the budget for limiting warming within Paris Agreement goals by 15-18%, equivalent to bringing forward the deadline for net zero by five to seven years. 
  • This means governments need to set far more ambitious mitigation targets to achieve net zero as defined by the IPCC, than covered by their current methods.
  • Differences in how emissions are reported from managed and unmanaged land in NDCs compared to the IPCC introduces opportunities for bias or misrepresentation, obscuring countries’ true climate impacts.
  • The amount of land designated for land-based removals in NDC pledges – about 1 billion hectares or the equivalent of around two-thirds of global arable land – is also impossible without complex trade-offs for food security, biodiversity and human livelihoods.
  • IPCC models give unrealistically optimistic estimates of land-based removal potential because they don’t consider land availability constraints, conflicts and human rights issues, or the erosion of land carbon sinks.
  • By comparison, a recent analysis modelling the social and ecological risks of land-based carbon removal potentially reduces the amount of land available for carbon removal by up to 79% compared to IPCC estimates.   
  • This discrepancy suggests that status quo estimates of land-based carbon removal used to inform global and national climate ambition may be overblown and misleading.

Emissions reduction in NDCs

Under the Paris Agreement, adopted in 2015, countries around the world agreed to submit climate action plans called Nationally Determined Contributions (NDCs) every five years starting in 2020 to address greenhouse gas emissions.1Each new NDC submitted needs to be more ambitious than the last. NDCs translate global agreements into specific national targets and are the key mechanism for countries to show their commitment to reducing emissions – through, for example, phasing out fossil fuels, deploying renewable energy, decarbonising industries and electrifying transport.

Another approach to reducing emissions involves harnessing the ability of landscapes to capture and store carbon – a greenhouse gas inventory sector referred to as land use, land-use change, and forestry (LULUCF) by the Intergovernmental Panel on Climate Change (IPCC).2LULUCF excludes non-carbon-dioxide agricultural emissions, such as methane from livestock. Natural landscapes around the world store significant amounts of carbon in plants and soil – global forests absorb an average of 7.6 billion metric tonnes of carbon dioxide per year, equivalent to around one and a half times the annual emissions of the US. 

In the LULUCF component of their NDCs, countries pledge to plant new forests (afforestation), restore degraded forests (reforestation), protect existing forests and implement sustainable forest management and soil conservation techniques. To a much lesser degree, they also project the use of bioenergy with carbon capture and storage (BECCS), whereby trees, crops or algae will, in theory, be grown to capture carbon dioxide from the atmosphere and then converted into energy, such as biofuels, with the emissions stored below ground.

These forms of carbon dioxide removal are appealing to governments and industries because they don’t necessitate immediate, large-scale changes to a country’s industrial and energy sectors.  However, although most IPCC pathways that aim to limit warming to Paris Agreement targets of 1.5°C or 2°C include carbon sequestration in land sinks, enhancing these sinks alone is insufficient to achieve the necessary carbon reductions. Ambitious and timely NDC commitments this decade could close the emissions gap needed to keep temperatures within targets but require a rapid shift away from traditional fossil fuels in addition to land-based removal. 

Due to several scientific and political reasons outlined below, the potential contribution of land carbon sequestration to emissions reductions is significantly overestimated in NDCs and scientific models. This overestimation renders the commitments outlined in NDCs unrealistic and endangers the goals of the Paris Agreement. While several publications have explored this issue, no comprehensive, easy-to-read resource has been created to synthesise the findings. The goal of this briefing is to provide a concise summary of the various reasons NDCs disproportionately rely on land for carbon removal and to outline the potential implications for the Paris Agreement.

Land carbon fluxes are the most uncertain component of the global carbon budget

Countries annually report their progress on the emissions reductions pledged in their NDCs through National Greenhouse Gas Inventories (NGHGIs), following guidelines established by the United Nations Framework Convention on Climate Change (UNFCCC). 

Collective progress towards the Paris Agreement goals is assessed every five years in the Global Stocktake, which provides benchmarks for countries for their NDC submissions. If NDCs are insufficient or lack ambition, there is a significant risk that the world will exceed the Global Carbon Budget – the total amount of carbon dioxide that can be emitted while keeping within global temperature targets, leading to temperature increases beyond the targets agreed upon in the Paris Agreement.

Because of the complex interactions of various human-driven effects on greenhouse gas fluxes from land – such as deforestation for agriculture – land carbon fluxes are the most uncertain component of the global carbon budget. At the national level, accurately tracking changes in forests and other land uses is also challenging due to variations in the quality and scope of land-use data, different reporting methods used, and difficulties in separating the influence of humans and climate on the environment as well as in reporting carbon movements in different ecosystems, with estimates relying significantly on simplified models. This means that estimates of emissions from LULUCF are less precise than those from fossil fuels, which are grounded in empirical data.

As a result, the Paris Agreement allows flexibility for countries to determine how they account for emissions and removals from the LULUCF sector, such as the use of different accounting and monitoring methods or different definitions of land-use types in their climate targets. In addition, developing countries are encouraged to gradually adopt economy-wide emission reduction targets depending on their economic and developmental needs. In comparison, developed countries are required to specify a specific, measurable and economy-wide reduction in overall emissions – for example, a 40% emissions reduction compared to 1990 levels.

NDC net-zero may not mean net-zero global emissions

The use of different carbon accounting methods for land-based removal between NDCs and model-based methods, such as those used by the IPCC, makes it hard to measure the emissions and temperature outcomes of current national commitments under the Paris Agreement. 

While both NGHGIs and the models used by the IPCC to assess the pathways necessary to achieve specific climate targets aim to identify greenhouse gas fluxes from land, they differ in how they account for the role of human activity in these fluxes. This affects the extent to which each approach attributes these fluxes to a country’s mitigation efforts.3One outcome is that estimates of land-use change due to afforestation or reforestation are in close agreement between NGHGIs and IPCC models, but differ for managed forests.

This is especially problematic for countries that rely heavily on the land sector and forest management to achieve their NDCs, leading to over- or under-estimating true emissions and creating inconsistencies between national inventories and the global carbon budget.

A recent analysis illustrated how current NGHGIs for NDCs can make national emissions appear lower than the method applied by the IPCC in assessing alignment with the Paris Agreement. It concluded that once the methods are harmonised – such as by adjusting fluxes from land use – our overall carbon budget is reduced by 15-18%, which is equivalent to bringing forward the deadline for net zero up by five to seven years. What this means is that governments need to set far more ambitious mitigation targets to achieve net zero, as defined by the IPCC.

Unmanaged land is a blind spot in carbon accounting

Discrepancies in the LULUCF emissions estimates between IPCC models and NDCs arise partly because countries are not required to report emissions from unmanaged land – such as emissions from wildfires in remote forests where human intervention is minimal or absent – as these are considered natural rather than human-caused emissions. This has resulted in some highly forested countries designating large areas of forest as unmanaged. But as emissions are still released from these unmanaged areas, excluding them leads to an incomplete picture of the carbon cycle and a country’s total emissions.

This has introduced opportunities for bias or misrepresentation. For example, Canada does not include emissions from forest wildfires in its inventory, as around 34% of its forests are classified as ‘unmanaged’. This means that emissions from natural disturbances, such as wildfires, in these forests are not accounted for.4The Canadian government does not have a database for the net carbon flux in unmanaged lands in the country, making it difficult to track carbon emissions and evaluate whether Canada’s landmass is sequestering enough carbon to offset its emissions. Additionally, fires within its managed forests are also classified as natural disturbances rather than human-caused disturbances, and so are also excluded from the inventory.

This oversight leaves significant emissions unaccounted for, obscuring Canada’s true climate impact. Around 114 million metric tonnes of emissions was excluded per year from its inventory between 2005 and 2021 – equivalent to around half the total carbon dioxide emissions from gas in Canada in 2023.5This is compounded by the fact that Canada classifies removals from mature forests as human-caused. In 2023, a year of record-breaking wildfires, natural disturbances released an estimated 640 million metric tonnes of carbon from Canada’s forests, which is more than Canada’s carbon dioxide emissions from fossil fuels in 2022.

Managed land can lead to overestimates of climate progress 

Flexible guidelines also mean that there is variation in what constitutes managed and unmanaged land. Under the Kyoto Protocol adopted in 1997, countries agreed to count greenhouse gas emissions and removals from land activities towards their climate targets only if they result from direct human actions. However, the IPCC later noted that as human activities and environmental changes are closely linked, they are not practical to separate in greenhouse gas inventories – for example, forest loss from both logging and climate-induced drought. Therefore, ‘managed land’ was introduced as a proxy for human effects in NDC guidelines, with all greenhouse gas fluxes occurring on managed land being counted regardless of whether they are driven by humans or the environment. This is not a feature of the IPCC’s models that are used for estimating carbon fluxes, which clearly distinguish between emissions from managed and unmanaged forests. 

This means that countries can classify natural forests as managed land in their NGHGIs, enabling them to report natural carbon removal as emissions reductions. Including natural land as managed land can also give a misleading picture of a country’s actual climate efforts by overestimating carbon removals and making progress seem greater than it is. This is further aggravated by the fact that some countries – particularly those that are afforded flexibility in emissions accounting – also report implausibly high forest sinks, have incomplete assessments or have inconsistent estimates across reports. Some forest-dense countries are claiming credit for the carbon that their unmanaged forests are sequestering, using this as a means to justify fossil fuel extraction while also making net-zero claims.

Land-based removal plans are unrealistic

The lack of stringent accounting guidelines has led to a significant over-allocation of land for carbon removal in NDC pledges, beyond what is technically feasible or safe. The Land Gap Report calculated that there is about 1 billion hectares of land for land-based carbon removal included in NDC pledges to 2060 – equivalent to around two-thirds of the world’s arable land and a land area bigger than China. Such large-scale commitments would be impossible without catastrophic impacts, including the displacement of food production and threats to biodiversity. 

Pledges for land-based removal in NDCs rely heavily on planting new forests or plantations, with about half of the land proposed for carbon removal in NDCs requiring changes in present land use. Land-use change is already the biggest driver of biodiversity loss, which is essential for ecosystem resilience and the provision of ecosystem services such as food and water security and carbon sequestration.6Agricultural land is already under significant pressure from rising global food demand, expanding populations and the need to balance land use with biodiversity conservation and climate mitigation efforts. A 2022 analysis estimated that afforestation and bioenergy production could place an additional 41.9 million people at risk of hunger by 2050 due to higher food prices and displacement of agricultural land

In addition to the risks around increased competition for land use, estimates suggest that the ‘safe limit’ for expanding agriculture has already been passed, resulting in ecosystem degradation. Figure 1 shows that global cropland already exceeds the planetary boundary for sustainable land use, with land-use changes in pledges and current and projected BECCS projects adding nearly an extra two-thirds to the current land-use change area. There is very little land left that can be used for carbon dioxide removal without complex trade-offs. To be genuinely effective, carbon removals plans need to factor in ecological limits and support biodiversity.

Figure 1. Land for mitigation crosses planetary boundary thresholds
Source: The Land Gap Report, 2022.

Even if the estimates of removal potential from land in NDCs were technically feasible, a 2023 analysis calculated that current NDCs are insufficient for meeting Paris Agreement targets – actions outlined in NDCs are due to result in warming of 2.5-2.9°C by 2100.

Limitations in IPCC models of future land carbon removal 

While NDCs focus on near-term actions to reduce greenhouse gas emissions, Integrated Assessment Models (IAMs) used by the IPCC project long-term scenarios for achieving climate goals. IAMs assess the interactions between climate, energy, land use and economic systems to understand the long-term implications of different policy choices and emissions trajectories, offering different pathways that illustrate how various strategies can achieve climate targets. IPCC pathways offer a framework for countries to set their emissions reduction targets and to align their NDCs to demonstrate their commitment to international climate agreements.

However, recent research argues that the methodologies in IPCC models are over-relying on land-based removal by building in assumptions about land use that are unrealistic. The models do not reflect real-world conditions such as land availability, lack nuance by failing to capture the complexities of human systems and ecosystems, and expose vulnerable communities to avoidable risks. As IPCC reports are the primary mechanism informing the UNFCCC, inappropriate models have the potential to lead to misguided policies and ineffective climate action, ultimately hindering efforts to reduce greenhouse gas emissions and meet international climate goals.

Hidden assumptions mean models over-rely on land

A key challenge with the representation of land-based carbon removal in IAMs is the assumption that significant emissions generated in the near term will be offset in the distant future through decades of land-based removal. 

Because of their emphasis on cost-effectiveness, least-cost pathways and supply-side technologies, IAMs often assume that large-scale BECCS and afforestation projects can be implemented easily, without considering competing demands for land. This leads to overestimations of the amount of land available for future carbon removal in the LULUCF sector. To demonstrate this, a 2018 study assessed the rate at which land uses change in IAMs and found that in scenarios limiting warming to 2°C by 2100, cropland for BECCS is projected to expand by 8.8 million hectares per year. This expansion rate is more than three times as fast as the historical expansion of soybean, which is currently the fastest-growing commodity crop and a significant driver of deforestation in the Amazon. 

IAMs also have idealised assumptions that do not fully consider the technical, social and economic barriers to scaling up such efforts, such as land tenure issues, governance challenges, the potential for conflict over land use​ and human rights issues, including rights to food, water and a healthy environment. 

IAMs are built on assumptions of ‘empty land’ that do not consider nomadic or Indigenous lifestyles or non-forest ecosystems, such as savannas, and also broadly assume that forests can be converted to cropland for bioenergy. BECCS only features in the NDCs of seven countries, totalling 80 million hectares of land, but it is much more prominent in modelled IPCC pathways, with a median land demand of 199 million hectares (ranging from 56 million to 482 million hectares) in 1.5°C-consistent pathways. However, given such a significant land demand for BECCS from a small number of countries in current NDCs, a land demand of 199 million hectares in future pathways is likely to be an underestimate if BECCS becomes as widespread as in modelled pathways.

The models have also been criticised by researchers for being opaque, with specific value judgments about the future buried in the mathematics of the model. By assuming that the financial costs of mitigation technologies will fall in the future – through applying a high discount rate in the model – solutions like BECCS, which has not yet been proven to work at scale, can appear more cost-effective than proven, readily implementable actions. As BECCS is considered ‘carbon neutral’ in the models, many IAMs also favour large-scale BECCS over renewable technologies to meet the requirements of one of the more ambitious climate pathways that assumes significant reductions in greenhouse gas emissions.7The RCP 2.6 emissions pathway in the IPCC’s Sixth Assessment Report.

A 2024 analysis found that a high discount rate in IAM models favours high overshoot scenarios – where global average temperatures temporarily exceed a warming target before dropping back down to, or below, the target in the future – rather than scenarios that would mitigate long-term warming effects. This is because of the short timescale over which economic adaptation is assessed in the models. These high overshoot scenarios result in a heavy reliance on land-based carbon dioxide removal in the future as emissions are not reduced fast enough to limit warming. Overshoot is estimated to be cheaper than longer-term solutions and is therefore favoured by the models. However, overshoot comes with various risks and uncertainties, such as species extinction and ecosystem collapse, and has potentially irreversible consequences. Overshoot also raises moral concerns, as climate-related impacts disproportionately affect vulnerable populations, especially in low-income countries.

Reliance on land carbon removal raises sustainability risks

A recent analysis proposed thresholds for land-based sequestration that account for social and ecological risks, thereby developing realistic and sustainable estimates for land-based CDR while accounting for environmental and resource limits (Table 1).​ The analysis estimates that the sustainable potential of LULUCF measures for carbon removal, including limited reforestation, forest restoration, reduced forest harvest, agroforestry and silvopasture, and BECCS is  3.3 billion-3.8 billion tonnes per year.8Values obtained from Supplementary Table S1 in the report.

The study finds that at high sustainability risk – the point at which multiple ecological and social sustainability limits are likely to be overstepped with potentially irreversible consequences – the value is 6.4 billion tonnes per year. These estimates of sustainable – and hence feasible – removal potential are more conservative than the average estimates in the IPCC’s Sixth Assessment Report – 15.6 billion metric tonnes of carbon dioxide per year between 2020 and 2050 for BECCS, forest and ecosystem protection, restoration and management, and agroforestry, as well as the Emissions Gap Report which included estimates of 5.9 billion tonnes per year by 2030 and 8.4 billion tonnes by 2035 for forestry-related land management,9Values obtained from Table 6.2: Sectoral mitigation potentials in 2030 and 2035. and the State of CDR Report at 7 billion-9 billion metric tonnes by 2050 from forestry-related removal, BECCS, ecosystem restoration and novel technologies such as direct air capture. Compared to IPCC estimates, a low sustainability risk scenario potentially reduces land available for carbon removal by around 79%.10This is a rough calculation assuming a direct comparison between land-use footprint in the IPCC technical mitigation potential and the analysis in Deprez et al. (2024) and was calculated as the difference between the IPCC estimates of 15.6 billion metric tonnes and the lower sustainability risk estimate of 3.3 billion tonnes.

Overall, the greatest risks are linked to scenarios with slower emission reductions and higher reliance on future carbon removal technologies. This highlights the need to reduce emissions quickly and significantly and not rely on future carbon removals – including from land – in order to avoid the worst outcomes.

Table 1. Sustainability risks for land-based carbon dioxide removal for the five IPCC Illustrative Mitigation Pathways compatible with the Paris Agreement.
Data source: Sustainability limits needed for CO2 removal, 2024.  
A/R refers to afforestation/reforestation. BECCS & A/R larger footprint assumes a low capture rate and conversion efficiency, while BECCS & A/R medium footprint assumes a medium capture rate and conversion efficiency.
Models do not account for land’s declining ability to store carbon

As IAMs are global in scale, their assumptions are simplified and generalised, and therefore they can miss key local dynamics, leading to ill-suited projections at the regional level​.11The IPCC recommends that these models are interpreted in the context of their assumptions. IAMs often oversimplify ecosystems, which do not always behave linearly in response to human activities or climate change. For instance, land-use changes can trigger feedback loops that are difficult to capture accurately in simplified models. A 2024 analysis found that IAMs tend to underestimate the risks associated with the interaction between wildfire disturbances and climate change, particularly regarding their impact on the ability of forests to sequester carbon, risking an overly-optimistic estimate of how much carbon forests can remove and store, and inaccurate predictions of future emissions​.

This is significant because land and ocean sinks are increasingly absorbing less carbon with rising temperatures. In higher emissions scenarios, the interaction between climate change and the carbon cycle becomes more uncertain due to the risk of positive feedback loops – such as forest fires and permafrost thaw – amplifying climate change impacts. These types of ecosystem responses are not fully integrated into models simply because of their sheer complexity. While models have tended to predict a slow erosion of natural carbon sinks over the next 100 years or so, other estimates suggest that the impact from feedback loops is happening much sooner than anticipated.

  • 1
    Each new NDC submitted needs to be more ambitious than the last.
  • 2
    LULUCF excludes non-carbon-dioxide agricultural emissions, such as methane from livestock.
  • 3
    One outcome is that estimates of land-use change due to afforestation or reforestation are in close agreement between NGHGIs and IPCC models, but differ for managed forests.
  • 4
    The Canadian government does not have a database for the net carbon flux in unmanaged lands in the country, making it difficult to track carbon emissions and evaluate whether Canada’s landmass is sequestering enough carbon to offset its emissions.
  • 5
    This is compounded by the fact that Canada classifies removals from mature forests as human-caused.
  • 6
    Agricultural land is already under significant pressure from rising global food demand, expanding populations and the need to balance land use with biodiversity conservation and climate mitigation efforts. A 2022 analysis estimated that afforestation and bioenergy production could place an additional 41.9 million people at risk of hunger by 2050 due to higher food prices and displacement of agricultural land
  • 7
    The RCP 2.6 emissions pathway in the IPCC’s Sixth Assessment Report.
  • 8
    Values obtained from Supplementary Table S1 in the report.
  • 9
    Values obtained from Table 6.2: Sectoral mitigation potentials in 2030 and 2035.
  • 10
    This is a rough calculation assuming a direct comparison between land-use footprint in the IPCC technical mitigation potential and the analysis in Deprez et al. (2024) and was calculated as the difference between the IPCC estimates of 15.6 billion metric tonnes and the lower sustainability risk estimate of 3.3 billion tonnes.
  • 11
    The IPCC recommends that these models are interpreted in the context of their assumptions.

Australia, a global climate outlier?

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Key points:

  • Australia’s environmental laws currently fall short in addressing climate change. The country does not have a climate trigger mechanism, despite having one of the highest rates of biodiversity loss in the world.
  • There is a growing number of countries, including the US, UK and New Zealand, that include climate change and emissions considerations in their environmental frameworks.
  • The Australian government’s stance on fossil fuels stands in contrast to warnings from international scientific bodies regarding the urgency of addressing climate change.
  • Australia could be responsible for up to 17% of global carbon dioxide emissions by 2030 if planned expansion of fossil fuels goes ahead.
  • The introduction of a climate trigger presents a chance for the country to align itself with global efforts in tackling GHG emissions from fossil fuel projects and reverse alarming environmental trends.

What is a climate trigger?

A climate trigger means governments have to consider the emissions and climate change impact of a project when assessing whether it should go ahead. Several countries and economies, including the US, UK, European Union, New Zealand and Canada, include assessments of greenhouse gas (GHG) emissions and other climate change considerations in their environmental regulatory frameworks. However, Australia currently has no explicit mechanism to account for climate change and the impacts of fossil fuel projects in its national environmental laws.

Australia’s environmental backbone

Australia has a dual approach to environmental governance, with individual states and territories having their own environmental laws and regulation, alongside national law governed primarily by the Environment Protection and Biodiversity Conservation Act (EPBC Act). While state and territory laws address environmental concerns within their jurisdictions, the EPBC Act serves as a comprehensive framework that complements and coordinates these efforts.

The EPBC Act designates nine key areas as matters of national environmental significance, or triggers, including specific regions, species and ecosystems that hold ecological value and require protection at the national level. If a project is deemed likely to have a significant impact on one of these areas, then a thorough impact assessment and environmental approval process is “triggered.”

The nine triggers identified under the EPBC Act are:
  1. World Heritage properties: These include the Great Barrier Reef and the Tasmanian Wilderness.
  2. National Heritage places: Sites recognised for their outstanding heritage value to the nation, such as iconic landmarks or culturally significant areas.
  3. Wetlands of international importance: Designated under the Ramsar Convention, an international treaty aimed at conserving key wetland ecosystems and their biodiversity.
  4. Listed threatened species and ecological communities: Endangered species and ecosystems that are at risk of extinction or significant decline.
  5. Listed migratory species: Migratory birds and marine species that require protection during seasonal movements across national and international borders.
  6. Commonwealth marine areas: The marine environment within Australia’s Exclusive Economic Zone, such as the Great Barrier Reef Marine Park.
  7. Nuclear actions: Activities related to uranium mining, nuclear power plants, and other nuclear-related actions.
  8. Water resources: The impacts of coal seam gas and large-scale coal mining on water quality and availability.
  9. The Great Barrier Reef: Activities that may impact water quality, coastal development and shipping activities
Criticism of current laws

The lack of a climate trigger has prompted concerns in Australia over the effectiveness of the EPBC Act, in which “climate change” appears just once, as well as the country’s commitment to the 2015 Paris Agreement. Advocates of a climate trigger argue that its omission results in insufficient scrutiny of activities. Projects with substantial climate impacts are allowed to proceed without undergoing the same rigorous assessments as those falling under other triggers, leading to potential habitat degradation and exposing ecosystems to climate-related risks.

Importance of climate trigger for Australia

Increasingly high temperatures, wildfires and other climate impacts have significantly disrupted numerous ecosystems and species in Australia. The country has one of the highest extinction rates of plant and animal species in the world. Since 1999, 84% of threatened species have experienced habitat loss. In the last seven years, Australia witnessed a series of marine heatwaves that lead to four mass coral bleaching events on the Great Barrier Reef, causing a 50% decline in the coral population. Climate change has the potential to exacerbate these losses by fivefold.

Climate triggers globally

Globally, there is a growing trend of countries incorporating climate change considerations into their national environmental frameworks, and the assessment of projects with large amounts of GHG by independent bodies has become standard practice. Examples include the EU, the UK, the US, Canada and New Zealand.

While the environmental frameworks of these countries differ in scope, enforceability and effectiveness, they all prioritise human well-being. The frameworks of the UK, US, and Canada do not explicitly mandate GHG assessments, but GHG considerations are indirectly addressed through other legal mechanisms. Climate change considerations, while not always explicitly mentioned, are increasingly woven into these frameworks, reflecting a global imperative to address climate-related challenges.

Table 1: Comparative analysis of environmental legislation

The countries chosen for analysis — the UK, EU, US, Canada and New Zealand — were selected based on several criteria to enable meaningful comparisons. New Zealand’s proximity to Australia provides regional relevance. The EU and UK dominate global climate discussions, while similarities in political systems led to the inclusion of Canada and the US.

Comparative-analysis-of-environmental-legislationDownload

Australia’s climate trigger proposal

The debate over whether to adopt a climate trigger mechanism in Australia has been ongoing for decades, and several proposals, including a bill submitted by then Shadow Minister for Environment and Heritage Anthony Albanese, failed to win enough support. This was due to concerns that such a trigger would harm jobs, economic development and investment, or clash with existing environmental legislation.

In 2020, a review of the EPBC Act found that it had failed to adequately protect Australia’s vulnerable flora, fauna and ecological communities. The Australian government has committed to revising the Act, and in December 2022 a series of reforms were proposed by the government to be adopted in late 2023. However, climate change considerations were still not addressed.

The Australian Greens plan to submit a proposal for a climate trigger, in order to position the country on par with international trends. Building on an unsuccessful 2020 proposal, the new bill is expected to cover the following:

  • Ministerial authority on carbon dioxide emissions: the bill would grant the climate minister the authority to factor in GHG emissions when making project-related decisions. These powers are categorised into two thresholds:
  • Significant Impact on Emissions: Projects emitting 25,000 to 100,000 tonnes of GHG emissions annually must be evaluated by the ministry, ensuring alignment with the national carbon budget and emission reduction targets.
  • Prohibited Impact on Emissions: Projects emitting over 100,000 tonnes will automatically be denied approval.
  • Introduction of national carbon budget and enhanced roles for the Climate Change Authority (CCA): The CCA is an Australian government agency responsible for providing independent advice on climate change policy. If passed, the bill will mandate the CCA to develop a national carbon budget spanning from 2023 to 2049 in terms of total carbon dioxide equivalent emissions. The CCA must conduct annual evaluations of the remaining budget, while the minister is responsible for evaluating projects, considering the ongoing assessments of the budget.
How does Australia’s climate trigger compare globally?

While most laws discussed in Table 1 are undergoing revisions to better address the challenges posed by climate change, parallels can be drawn between some of them and Australia’s Climate Trigger proposal. Under the Climate Change Act 2008, the UK became the world’s first country to establish legally binding carbon budgets. The measure closely resembles what the Climate Trigger bill aims to introduce in Australia — a national carbon budget, accompanied by annual evaluation of new projects. In Canada, the environment minister was also given authority to require assessments for certain projects if they could have adverse climate impacts. These parallels underscore how Australia’s bill aligns with international efforts to address climate change and responsibly manage emissions, something that is argued to be lacking in the current EPBC Act.

However, what sets the Australian Greens’ bill apart from other laws is its commitment to explicit emissions thresholds. Among the countries examined, none of them automatically ban projects that exceed specific emissions limits. While this doesn’t prevent new fossil fuel projects being approved that emit more than initially estimated, it does pave the way for regulating these emissions.

Next steps for Australia’s climate trigger mechanism

The bill is currently under consideration by an environmental committee in the Australian Senate and a final ruling is expected in December 2023. A majority of lawmakers in parliament now recognize the need for government intervention in addressing climate change, and the crossbench offers strong support for a climate trigger.1The crossbench is where independent and minor party members sit in Australia’s parliament.

However, there has been a significant shift in the stance of Prime Minister Anthony Albanese and the Labor party since 2005. The current Labor government has ruled out a ban on new fossil fuel developments as long as investors perceive demand for coal and gas. It argues that introducing flexible measures, such as carbon offsets, would allow fossil fuel projects to proceed while still enabling the country to achieve its 43% emissions reduction target for 2030. The government’s position diverges from the warnings of organisations such as the United Nations, and leading climate science bodies such as the Intergovernmental Panel on Climate Change and the International Energy Agency.

Australia is the world’s third-largest exporter of fossil fuels behind Russia and Saudi Arabia, accounting for about 7%. In 2022, Australia had twice the electricity use per capita of China, and 47% of its electricity was generated by coal-fired power plants — more than four times the global average. Since 2014, the expansion of LNG production in Australia has grown by 360%, leading to a significant increase in national emissions levels. By 2030, Australia could potentially be responsible for up to 17% of global emissions, up from about 5% currently, if government and industry projections for fossil fuel expansion go ahead.

The Climate Trigger bill offers Australia the opportunity to take accountability for its emissions and the global harm caused by fossil fuels extracted within the country. If passed, it may help to reverse concerning environmental and biodiversity trends.2Assumes that the rest of the world adopts policies in line with the Paris Agreement.

  • 1
    The crossbench is where independent and minor party members sit in Australia’s parliament.
  • 2
    Assumes that the rest of the world adopts policies in line with the Paris Agreement.

The impacts of El Niño on a warming planet

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Key points:

  • El Niño is a natural climate phenomenon, typically lasting 9-12 months, that has been linked to crop failures, more frequent wildfires and concurrent droughts, increased flood risk, disruptions to fisheries, elevated civil conflict and increased disease risk in various regions
  • Present forecasts predict an 84% chance of at least a moderate El Niño and a ±56% chance of a strong El Niño for 2023-2024
  • The first year that we see average temperatures exceed 1.5°C could be during El Niño. While this would not mean that the Paris Agreement target has been transgressed, it is a reminder that we are getting closer to this threshold    
  • The frequency and severity of El Niño events increased in the latter part of the 20th century, and climate change is projected to further increase both, as well as making these events more difficult to predict
  • El Niño involves complex interplay among various atmospheric phenomena, making its impacts difficult to predict. However, it is associated with some general weather trends around the world, including:
    • Increased rainfall and flooding risk in East Africa, northern Mexico, the southern US, Peru and Ecuador  
    • Elevated fire risk in Indonesia, Australia and the Amazon 
    • Drought conditions in India, southern Africa, the Philippines, Indonesia, the Amazon and Australia  
    • Warm conditions in Canada and the northern US
  • Countries and ecosystems are already experiencing impacts from climate change, such as heatwaves, droughts and floods, and El Niño is likely to make these impacts worse.

El Niño

First described by Peruvian fishermen in the late nineteenth century as warm ocean waters around Christmas time that disrupt fishing conditions, El Niño is a natural climate phenomenon in which sea surface temperatures in the tropical Pacific are warmer than average. Under normal (or neutral) atmospheric conditions, trade winds – the east-to-west winds that blow along the earth’s equator – transport warm water from South America to Asia, which is then replaced by cooler water from lower depths. This process, referred to as upwelling, brings nutrients to the surface water, creating fertile fishing grounds. During an El Niño event, the trade winds weaken, causing warm water to accumulate in the Pacific Ocean. By contrast, when the trade winds are strong, the opposite happens and more warm water is transported to Asia – called a La Niña event. These two opposing processes – El Niño and La Niña – make up the El Niño-Southern Oscillation (ENSO) cycle. 

In the past, ENSO events were described as Eastern-Pacific (EP) events, because the Eastern Pacific was where the maximum warming was located. However, the last four decades have seen an increase in the frequency of Central-Pacific (CP) events,1CP El Niño events are also referred to as “El Niño Modoki” and “warm pool El Niño”. where the maximum warming is located in the central equatorial Pacific. The characteristics and associated impacts of these two events differ.2EP ENSO has stronger El Niño events compared to La Niña events, whereas CP ENSO has stronger La Niña events compared to El Niño events.   

The latest El Niño forecast, issued in June this year by the National Oceanic and Atmospheric Administration, states that El Niño has started and is expected to gradually strengthen during the Northern Hemispheric winter of 2023-2024. There is a ±56% chance of a strong El Niño and an 84% chance of a moderate El Niño. This prediction comes after an unusually long La Niña event lasting three years came to an end earlier this year. This was linked to catastrophic flooding in South-east Asia and Australia, particularly in Pakistan, where flooding displaced around eight million people, as well as the most severe drought in recent history in the Horn of Africa, which has left millions of people displaced and at risk of starvation.

Impacts of El Niño

Though the effects were originally thought to be localised to the coastal regions of Peru and Ecuador, it is now known that the impacts of El Niño, as well as its cooler counterpart La Niña, are global and have been linked to crop failures, increased wildfire frequency, increased flood risk, heightened concurrent drought frequency, disruptions to fisheries, increased civil conflict and higher disease risk in various regions of the world.

El Niño and climate change

The occurrence of extreme El Niño and La Niña events has increased since the 1960s, and climate projections suggest the frequency of extreme ENSO events will increase in the future.3The IPCC AR6 WGI report states that “a robust increase in ENSO rainfall amplitude [used for defining extreme El Niños and La Niñas] is found particularly in SSP2‑4.5, SSP3‑7.0, and SSP5‑8.5… The changes in ENSO rainfall amplitude in the long-term future (2081–2100) relative to the recent past (1995–2014) are statistically significant at the 95% confidence [level]”.While climate models do not show consensus regarding changes in ENSO sea surface temperature variability, models that simulate extreme ENSO events do show large agreement. Some projections suggest a doubling of extreme El Niño events as global temperatures continue to rise.4The future period in the study included projections until 2090. CP El Niño events are expected to become more frequent with climate change, while EP events are projected to become more extreme. 

During the second half of the 20th century, various changes to the behaviour of ENSO were observed, including: 

  • An increase in the occurrence of CP El Niño events   
  • Increased frequency of more extreme El Niño and La Niña events  
  • Increased variability of both CP and EP ENSO events  
  • Changes in the origin of both CP and EP ENSO events since the 1970s from the western Pacific to the central and eastern Pacific. 

As ENSO is a naturally highly variable phenomenon, determining whether the characteristics of ENSO events since the 1950s are the result of human-caused global warming, or simply a reflection of this inherent variability, is not straightforward, partly because sea surface temperature records before 1950 are sparse and unreliable.5In the IPCC AR6 WGI report it states that “there is medium confidence that both ENSO amplitude and the frequency of high-magnitude events since 1950 are higher than over the period from 1850 and possibly as far back as 1400”. Estimates using paleoclimate proxy data – which can be found in coral fossils and tree rings, for example – suggest that ENSO variability intensified by around 25% during the latter part of the 20th century compared to pre-industrial times.6Paleo-reconstructions typically have large uncertainty. A study published earlier this year estimates that human-caused warming has led to approximately one additional CP El Niño event and two additional extreme El Niño events since 1980. Despite the uncertainties, there is a growing consensus that human-caused warming is at least partly responsible for the changes in ENSO variability since the 1960s.

Record high sea temperatures in April this year may also worsen the upcoming El Niño event. We are likely to see record-breaking temperatures with this year’s El Niño, which is occurring against a backdrop of a warming earth – the last eight years were the world’s hottest on record. The hottest of these was in 2016 during one of the strongest El Niño events on record, which saw unparalleled coral heat stress in the world’s oceans resulting in extensive coral bleaching and die-off. ‘Pulse heat stress’ events, such as El Niño, may compound climate change-related stresses on humans and other organisms, with potentially irreversible consequences.7For instance, the 1982/1983 ​​El Niño event led to the possible extinction of a coral species in Panama.

It is more likely than not that global average temperatures will temporarily exceed 1.5°C above pre-industrial levels for the first time in human history between 2023 and 2027.8A 66% chance of exceeding 1.5°C for one year, according to the World Meteorological Organisation’s Global Annual to Decade Climate Update. It is unlikely (33% chance) that the 5-year average temperature will remain above 1.5°C between 2023 and 2027.  During an extreme El Niño event, an extra 0.2°C could be added to the average temperature of the earth on top of elevated temperatures due to global warming. The first year that we see average temperatures exceed 1.5°C could be during El Niño. While this would not mean that the Paris Agreement target has been transgressed, it is a reminder that we are getting closer to this threshold.9Breaching the Paris Agreement target of 1.5°C of warming since pre-industrial times – a threshold seen as important for limiting the impacts of climate change on people and nature – would require several decades of average temperatures above 1.5°C.  

Countries and ecosystems are already experiencing climate change-induced impacts, such as heatwaves, droughts and floods, and El Niño is likely to make these impacts worse. It has also been suggested that continued global warming is making it increasingly difficult to predict El Niño events.

Regional impacts

Predicting whether an El Niño event will occur, or how intense it will be, is challenging, mainly because predictions need to consider changes in both the Pacific Ocean and the atmosphere. While the characteristics of every El Niño event are different, our understanding of ‘teleconnections’ – whereby a climatic pattern, such as El Niño, is correlated with weather patterns elsewhere in the world – can be used to make predictions about the possible impacts. The figure below shows the typical weather impacts of El Niño across the world.

Source: National Oceanic and Atmospheric Administration
Africa

In East Africa, El Niño conditions tend to result in wetter ‘short rains’ (the second rainy season in November and December), which can cause flooding. There is also a strong link between the Indian Ocean Dipole (IOD) – the Indian Ocean counterpart of El Niño and La Niña, in which there is a difference in sea surface temperatures between the western and eastern Indian Ocean – and El Niño. When there is a positive IOD and EP El Niño, wetter short rains are amplified. 

In southern Africa, drier than average conditions are expected under El Niño, resulting in decreased maize yields, while the opposite is anticipated in East Africa. In Kenya, the higher rainfall associated with the 2015-2017 El Niño cycle increased maize production by 17%, while drought conditions in southern Africa during the same period reduced maize yields by up to 50%, caused the death of around 634,000 cattle, and resulted in more than 20 million people needing humanitarian aid. By contrast, wheat yields in South Africa may benefit from El Niño. 

During and after El Niño events, cholera incidence has been found to increase threefold in El Niño-sensitive areas in East Africa due to higher rainfall.

India

For India, El Niño tends to weaken the monsoon rains and produce drier conditions, and experts warn that when an El Niño event follows from a La Niña year – as is the case in 2023 – the monsoon rains may be particularly low.10Though this is dependent on various factors, such as lower Eurasian snow cover, which creates warmer conditions on the subcontinent, thereby bringing more rain to India. An assessment of rainfall trends over 132 years in India shows that severe droughts in the region have always been during El Niño years. Additionally, a CP El Niño event impacts the monsoon more than an EP event, but if an EP event occurs, there is also a higher possibility of a positive IOD occurring, which brings drier conditions to the eastern Indian Ocean (in the region of India) but wetter conditions to the western Indian Ocean (in the region of eastern Africa).

Southeast Asia

In Java, Indonesia, El Niño tends to decrease rainfall. Decreased rainfall during El Niño periods has been linked to increased forest fires in Indonesia and reduced rice yields on Java. where more than 50% of the country’s rice is grown. Fires in Indonesia are more intense and prolonged under an EP El Niño, and southern Kalimantan has experienced more intense fires than southern Sumatra under all El Niño events. However, fires are shorter and less intense during El Niño phases when the IOD is negative or weakly positive.     

In the Philippines, El Niño is associated with a decrease in average rainfall and elevated drought conditions, particularly during December to May. The associated water shortages may negatively impact agricultural production in the region – the 2015/2016 El Niño event cost USD 327 million in agricultural production losses. In China, El Niño is linked to higher wintertime air pollution due to southerly winds that encourage the accumulation of particulates.

Europe

El Niño winters are associated with wetter conditions in southern Europe and colder, drier conditions in northern Europe.

Australia

In Australia, El Niño is expected to bring higher temperatures and fire risk, and lower rainfall. Australia is warming faster than some other regions on earth – being 1.4°C warmer than it was during pre-industrial times – potentially making it particularly vulnerable to the effects of El Niño.

North America

In the Northern US and Canada, El Niño is associated with warmer conditions, whereas in the southern US and northern Mexico, wetter, cooler conditions with increased flooding risk are expected. El Niño weakens Atlantic hurricane activity but increases Pacific hurricane activity. 

El Niño may reduce wheat yields in the US as well as maize yields in the southeastern US, while soybean yields may increase.  

South America

El Niño typically brings heavier rains and flooding risk to Ecuador, Peru and Uruguay, A CP El Niño brings drier conditions to the tropical Andes and northern South America, but wetter conditions to southeastern South America and the Peruvian Amazon. An EP El Niño is linked to higher rainfall in Ecuador and Peru and dry conditions in northeastern Brazil, the Amazon Basin and the Andean Plateau. Specifically, an EP El Niño is associated with reduced rainfall in northern, eastern and western Amazonia, with significant impacts on water and carbon cycling – whereby carbon atoms are cycled between the atmosphere, organisms and minerals on earth. During EP El Niño events, lower rainfall occurs across all seasons in the Amazon, turning the Amazon into a net carbon source as trees dry out and slow their growth. During CP El Niño events, reduced rainfall is only observed during the summer wet season. Increased drought may drive forest fires and biome transformation in the Amazon. Warmer, drier conditions in Colombia during El Niño have been linked to outbreaks of dengue fever and malaria.

El Niño may positively affect maize production in Argentina and Brazil, soybean and rice production in Brazil, and wheat production in Argentina due to cooler and wetter conditions. In Mexico, El Niño could reduce maize and wheat output.

  • 1
    CP El Niño events are also referred to as “El Niño Modoki” and “warm pool El Niño”.
  • 2
    EP ENSO has stronger El Niño events compared to La Niña events, whereas CP ENSO has stronger La Niña events compared to El Niño events.   
  • 3
    The IPCC AR6 WGI report states that “a robust increase in ENSO rainfall amplitude [used for defining extreme El Niños and La Niñas] is found particularly in SSP2‑4.5, SSP3‑7.0, and SSP5‑8.5… The changes in ENSO rainfall amplitude in the long-term future (2081–2100) relative to the recent past (1995–2014) are statistically significant at the 95% confidence [level]”.While climate models do not show consensus regarding changes in ENSO sea surface temperature variability, models that simulate extreme ENSO events do show large agreement.
  • 4
    The future period in the study included projections until 2090.
  • 5
    In the IPCC AR6 WGI report it states that “there is medium confidence that both ENSO amplitude and the frequency of high-magnitude events since 1950 are higher than over the period from 1850 and possibly as far back as 1400”.
  • 6
    Paleo-reconstructions typically have large uncertainty.
  • 7
    For instance, the 1982/1983 ​​El Niño event led to the possible extinction of a coral species in Panama.
  • 8
    A 66% chance of exceeding 1.5°C for one year, according to the World Meteorological Organisation’s Global Annual to Decade Climate Update. It is unlikely (33% chance) that the 5-year average temperature will remain above 1.5°C between 2023 and 2027. 
  • 9
    Breaching the Paris Agreement target of 1.5°C of warming since pre-industrial times – a threshold seen as important for limiting the impacts of climate change on people and nature – would require several decades of average temperatures above 1.5°C.
  • 10

Key takeaways from the three working group reports of the IPCC sixth assessment

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Key points

  • Climate change is unequivocally caused by human activities as a result of burning fossil fuels, industrial processes and land use change and it is a threat to human well-being and planetary health.
  • Losses and damages from climate change will increase rapidly with further warming, in many cases creating risks that people and nature will be unable to adapt to. If emissions are cut at the rate currently planned, the resulting temperature rise will threaten food production, water supplies, human health, coastal settlements, national economies and the survival of much of the natural world.
  • To prevent further warming, urgent emission reductions across all sectors and rapid scale up of electrification are needed to reduce emissions and keep warming to 1.5°C by the end of the century. However, even the most ambitious scenarios indicate global temperatures will temporarily overshoot 1.5°C.
  • Models from the Working Group 1 and 3 report both indicate that deep reductions in other greenhouse gases, particularly in methane emissions, will help lower peak warming. 
  • Any further delay in concerted global action on adaptation and mitigation will miss a brief and rapidly-closing window of opportunity to secure a liveable and sustainable future for everyone.

IPCC’s sixth assessment cycle 

Between 2020 and 2022, the Intergovernmental Panel on Climate Change (IPCC) released three reports from its sixth assessment cycle covering the latest science on the physical state of the global climate (Working Group 1, WGI), the impact of climate change (Working Group 2, WGII) and mitigation of climate change (Working Group 3, WGIII). 

The sixth assessment cycle (AR6)  included 782 scientists, who worked on a voluntary basis, with 67 countries contributing to create the most authoritative assessment of climate change to date. 

This briefing summarises key themes that run through these three reports: 

  • The human-driven impact of climate change
  • The cause and current trajectory of our climate crisis
  • The speed and scale of the transformation required to achieve a safe(r) climate

Climate change is happening all around us 

The term “unequivocal” was used in both WG1 and WG2 to describe the scientific consensus that the climate is changing as a result of human activity, representing a threat to human well-being, societies and the natural world.1WG1, SPM A.1, WG2, SPM D.5.3. Human actions have warmed the climate at a rate that is unprecedented in at least the last 2,000 years, increasing the frequency and intensity of extreme weather events across the world. 2WG1, SPM1.WG2,SPM B.1.1 The physical impact of climate change is causing substantial damages and, in some cases, irreversible losses.3WG2,SPM B.1.1 

The WG2 report emphasised that we have a brief and rapidly-closing window of opportunity to secure a liveable future. Additionally, WG3 stressed that without urgent, effective and equitable mitigation, climate change increasingly threatens the health and livelihoods of people around the globe, ecosystem health and biodiversity.4WG2, SPM D.5.3 and WG3, SPM D.1.1

National commitments made by governments prior to COP26 are not enough to limit warming to 1.5°C and are likely to lead to global warming of 2.8°C by 2100. 5WG3, SPM B.6.WG3, SPM C.1.1. Both WG1 and WG3 reports agreed that even in the most ambitious emissions reduction scenario, it is more likely than not that global warming will reach 1.5°C by 2030 and overshoot to 1.6°C, before dropping back down.6WG1 Table SPM1, WG3, SPM Table SPM 2

The WG2 report described the devastating impacts of our current emissions pathway:

  • Food production and food security will be threatened by even a small amount of additional warming, which will cause increases in the severity and frequency of heatwaves, droughts and floods, along with sea-level rise7WG2, SPM B.4.3.
  • If warming reaches 2°C, there will be significant increases in ill-health and premature death as a result of more extreme weather and heatwaves, and disease spread8WG2, SPM B.4.4.
  • The extinction risk for unique and threatened species will be at least 10 times higher if temperature rise continues to 3°C, compared with if it is limited to 1.5°C.9WG2, SPM B.6.4.

Reliance on fossil fuels is the root cause of climate change 

Human activities around fossil fuel combustion, industrial processes, land use change and forestry have caused greenhouse gas (GHG) emissions to increase dramatically since pre-industrial times, and emissions were higher between 2010-2019 than in any previous decade.10WG3, SPM B.1, Footnote 6WG3, SPM B.1. Of the GHGs, CO2 has contributed the most to recorded warming to date, followed by methane.11WG1, Figure SPM2.WG1 D.1.7, Figure SPM2
In 2019, coal contributed to 33% of all human-related CO2 emissions, followed by oil (29%) and gas (18%).12WG3, Technical Summary, Figure TS.3. Public and private finance continue to flow into fossil fuels and, as a result, GHG emissions continue to rise across all sectors and subsectors, and most rapidly in transport and industry. 13WG3, Technical Summary, page 23.WG3, SPM B.5.4. Between 2019-2020, investment in fossil fuels was greater than that for climate adaptation and mitigation.14WG3, SPM B.5.4. In the power sector, fossil fuel-related investment was, on average, USD 120 billion a year. An average of USD 650 billion were invested in the oil supply and USD 100 billion in coal supply.15WG3, Chapter 15, 15.3.3. In comparison, actual global public finance flow for adaptation was USD 46 billion.16WG3, Chapter 15, 15.1.1.

Delayed climate action in reducing our reliance on fossil fuels is partly the result of a concerted effort to generate rhetoric and misinformation that undermines climate science and disregards risk and urgency.17WG2, Chapter 14, 14.3.1. This is particularly true in the US, where despite scientific certainty of the anthropogenic influence on climate change, misinformation and politicisation of climate change science has created polarisation in public and policy domains.18WG2, Chapter 14, 14.3.1.

People who have contributed the least to the existing climate crisis are likely to be the most vulnerable and least able to adapt. The richest 10% of households contribute about 36%-45% of global GHG emissions. About two thirds of the top 10% richest households live in developed countries.19WG3, Technical Summary, page 21. But increased heavy rain, tropical cyclones and drought will force more people from their homes, particularly in places that are more vulnerable and have less ability to adapt.20WG2 SPM B.4.7. 

Urgent, transformative change is needed to limit global warming

To limit warming to 1.5°C, we need to drastically reduce our reliance on fossil fuels for energy production and switch to widespread electrification using renewable energy generation. 21WG3, SPM C.3.2.WG3, SPM C.3.2. Changing how electricity is generated is especially important in transitioning our energy system, and in scenarios limiting warming to 1.5°C (with no or limited overshoot), the electricity sector reaches net-zero CO2 emissions globally between 2045 and 2055.22WG3, Chapter 6, Executive summary. In these scenarios, electricity supply rises to 48%-58% of final energy use by 2050 (in comparison to 20% in 2019).23WG3, Chapter 6, Executive summary. A combination of widespread electrification of all energy demand and a shift to renewable electricity systems that emit no CO2 will create co-benefits such as better health and cleaner air.24WG3, SPM C.4.1, SPM E.2.2.

We also need to have strong, rapid and sustained reductions in methane emissions. Models show that reducing methane emissions by a third by 2030 is needed to create a net cooling effect. 25WG3, SPM C.1.2.WG2, SPM D.1.7. Deep GHG emission reductions by 2030 and 2040 – particularly reductions of methane emissions – lower peak warming, reduce the likelihood of overshooting warming limits and lead to less reliance on net negative CO2 emissions that reverse warming in the latter half of the century.26WG2, SPM C.2.

Global use of coal, oil and gas (without CCS) is reduced by 100%, 60% and 70% respectively by 2050 in pathways that successfully limit warming to 1.5°C with no or limited overshoot.27WG3, SPM C.3.2. If not phased out, existing and planned fossil fuel infrastructure (without CCS) will make limiting warming to 1.5°C impossible.28WG3, SPM B.7

Rapid and deeper near-term GHG emissions reduction through to 2030 will lead to less reliance on carbon dioxide removal (CDR) in the longer term, but it is likely that we will need some CDR to counterbalance residual GHG emissions from hard-to-abate sectors.29WG3, SPM C.2.2, SPM C.3

CDR is not a ‘get out of jail free card’, especially at higher levels of warming because the ability of land and ocean sinks to sequester carbon will be greatly reduced at higher temperatures.30WG1, Figure 7 CDR also has limited ability to preserve existing ecosystems. If temperature rise passes 1.5°C, entire ecosystems will be irreversibly lost (including polar, mountain and coastal ecosystems, and regions that would be affected by ice-sheet and glacier melting),  even if temperatures are later reduced with measures to remove CO2 from the atmosphere.31WG2, SPM B.6.1

Some progress is being made

The WG3 report made it clear that there are mitigation options available in all sectors that could together halve global GHG emissions by 2030.32WG3, SPM C.12.1 Growing numbers of countries have seen the advent of cheap renewables that will power electric vehicles, heat pumps and other smart, emissions-free technologies. 

From 2010–2019, there were sustained decreases in the unit costs of solar energy (85%), wind energy (55%) and lithium-ion batteries (85%), and large increases in their deployment – for example >10x for solar and >100x for electric vehicles (EVs).33WG3, SPM Figure SPM 3 PV, onshore and offshore wind can now compete with fossil fuels on the levelised cost of energy in many places and electricity systems in some countries and regions are already predominantly powered by renewables.34WG3, Figure SPM 3, C.4.3 Large scale battery storage on electricity grids is increasingly viable.35WG3, Chapter 6, Executive summary

Electric vehicles are increasingly competitive against internal combustion engines, and it is the fastest growing segment of the automobile industry, having achieved double-digit market share by 2020 in many countries.36WG3, SPM Table TS.1  Electrification of public transport has been demonstrated as a feasible, scalable and affordable option to decarbonise mass transportation. 

There is also some green shoots evidence of climate policy beginning to have a positive real-world impact on emissions reductions that can be built on, for example:

  • At least 18 countries have now sustained production-based GHG and consumption-based CO2 emissions reductions for longer than 10 years.37WG3, SPM B.3.5
  • By 2020, over 20% of global GHG emissions were covered by carbon taxes or emissions trading systems, although coverage and prices have been insufficient to drive deep reductions.38WG3, SPM B.5.2
  • There are now ‘direct’ climate laws focused on GHG reduction in 56 countries covering 53% of global emission in 2020, and climate litigation is on the rise.39WG3, SPM B.5.2, E3.3
  • 1
    WG1, SPM A.1, WG2, SPM D.5.3.
  • 2
    WG1, SPM1.WG2,SPM B.1.1
  • 3
    WG2,SPM B.1.1
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    WG2, SPM D.5.3 and WG3, SPM D.1.1
  • 5
    WG3, SPM B.6.WG3, SPM C.1.1.
  • 6
    WG1 Table SPM1, WG3, SPM Table SPM 2
  • 7
    WG2, SPM B.4.3.
  • 8
    WG2, SPM B.4.4.
  • 9
    WG2, SPM B.6.4.
  • 10
    WG3, SPM B.1, Footnote 6WG3, SPM B.1.
  • 11
    WG1, Figure SPM2.WG1 D.1.7, Figure SPM2
  • 12
    WG3, Technical Summary, Figure TS.3.
  • 13
    WG3, Technical Summary, page 23.WG3, SPM B.5.4.
  • 14
    WG3, SPM B.5.4.
  • 15
    WG3, Chapter 15, 15.3.3.
  • 16
    WG3, Chapter 15, 15.1.1.
  • 17
    WG2, Chapter 14, 14.3.1.
  • 18
    WG2, Chapter 14, 14.3.1.
  • 19
    WG3, Technical Summary, page 21.
  • 20
    WG2 SPM B.4.7.
  • 21
    WG3, SPM C.3.2.WG3, SPM C.3.2.
  • 22
    WG3, Chapter 6, Executive summary.
  • 23
    WG3, Chapter 6, Executive summary.
  • 24
    WG3, SPM C.4.1, SPM E.2.2.
  • 25
    WG3, SPM C.1.2.WG2, SPM D.1.7.
  • 26
    WG2, SPM C.2.
  • 27
    WG3, SPM C.3.2.
  • 28
    WG3, SPM B.7
  • 29
    WG3, SPM C.2.2, SPM C.3
  • 30
    WG1, Figure 7
  • 31
    WG2, SPM B.6.1
  • 32
    WG3, SPM C.12.1
  • 33
    WG3, SPM Figure SPM 3
  • 34
    WG3, Figure SPM 3, C.4.3
  • 35
    WG3, Chapter 6, Executive summary
  • 36
    WG3, SPM Table TS.1
  • 37
    WG3, SPM B.3.5
  • 38
    WG3, SPM B.5.2
  • 39
    WG3, SPM B.5.2, E3.3

IPCC Sixth Assessment Report: Mitigation of climate change

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The Intergovernmental Panel on Climate Change (IPCC) has released the third of its four-part, Sixth Assessment Report (AR6) in April 2022. The Working Group III (AR6 WGIII) report is the most comprehensive review of how we can mitigate climate change since the 5th assessment (AR5) in 2014, and the IPCC’s three recent special reports (SR1.5 in 2018 and the 2019 SRCCL and SROCC). 1WGIII will be third of  four separate reports published in the AR6 cycle. ‘The Physical Science Basis’ which detailed the current state of the climate was published on 9 August 2021 and the second report ‘impacts, adaptation and vulnerability’ was released in March 2022.

The report has been ratified after a plenary negotiation in which governments formally approved the summary for policymakers, ensuring high credibility in both science and policy communities. The report covers a broad spectrum of topics, from mitigation pathways and in-depth sectoral analysis to finance, international cooperation, net-zero and carbon dioxide removal. For the first time in IPCC history, chapters dedicated to technology, innovation and demand-side measures are included.

This briefing covers some of the major developments in our knowledge of mitigation since the IPCC’s AR5 was published in 2014. Today, mitigation literature largely reflects the 2015 Paris Agreement, increasing net-zero commitments and the growing need for action from non-governmental stakeholders including businesses, industry and financial institutions.

1. Since AR5 greenhouse gas emissions have continued to climb

We are nowhere near on track to achieve the Paris targets of keeping warming below 2°C, and ideally 1.5°C. Current national climate plans (NDCs) will see us warm by about 2.7°C this century, or possibly even higher 2These numbers are based on pre-Glasgow estimates. If you add all pre-Glasgow net-zero pledges to the NDCs this brings the world on track for 2.2°C, according to UNEP (or about 2.1°C in IEA assessments), page 12, section 7 of the 2021 Emissions Gap Executive Summary..  If CO2 emissions continue at current rates, we will exhaust the remaining 1.5°C carbon budget in the early 2030s 3Most recent estimates show that only 440 Gt CO2 is left from 2020 to stand even a 50% chance of 1.5°C. Global emissions were over 40 Gt CO2 in 2019, and if annual emissions are similar in the next decade it will be used up in the 2030s.. The energy infrastructure from planned and current fossil fuels alone commits us to about 846 GtCO2 (more than double what’s left in our 1.5°C carbon budget) and every year we add more carbon-intensive infrastructure than we decommission. 

Of the greenhouse gases (GHGs), CO2 causes most warming due to its high concentration and long lifetime in the atmosphere. Despite efforts to reduce emissions, our burning of fossil fuels adds more CO2 to the atmosphere, pushing the cumulative atmospheric concentration to unsustainable highs. Between 1850-2019, coal, oil and gas accounted for ~66% of cumulative CO2 emissions, with land-use change responsible for about 32%. 

But since AR5, there has been greater recognition of increasing emissions of methane (CH4) and nitrous oxide (N2O). Both are potent GHGs that trap about 34 and 300 times more heat than CO2 respectively (over a 100 year period). Methane is responsible for almost a quarter of human-caused warming to date, and concentrations are increasing faster now than at any time since the 1980s. Today, methane emissions are two-and-a-half times above pre-industrial levels. The AR6 WGI SPM authors emphasised that “strong, rapid and sustained reductions” in methane emissions would have the dual impact of limiting “the warming effect resulting from declining aerosol pollution” and improving air quality.

Between 2008-2017, agriculture and waste contributed most to the rise, followed by the fossil fuel industry. However, estimating by exactly how much, and from where, methane emissions are increasing is a topic of continued research and debate. For example, some researchers have found that the role of North American shale gas (so called “fracking”) has been significantly underestimated in calculating the global methane emissions. 

Emissions of N2O have risen 20% from pre-industrial levels, with the fastest growth observed in the last 50 years, mainly due to nitrogen additions to croplands through fertilisers. 

In 2018, global GHG emissions were about 57% higher than in 1990 and about 43% higher than in 2000. Emissions continued to rise in 2019, when they reached about 59 GtCO2e. But in 2020, the COVID-19 pandemic led to a historical large drop in CO2 emissions from fossil fuels and industry. During the height of global lockdowns, daily emissions dropped by 17% compared to 2019, levels not seen since 2006, and people around the world were allowed a short respite from deadly air pollution. Since then, emissions have rebounded, and were the highest yet last year. However, research has shown that rebuilding the economy in a more green, sustainable, just and climate-centred way represents a far greater opportunity than the short, lockdown-triggered emissions break, which will have little impact in the long run.

2. Without a drastic boost in climate ambition, our hopes of  achieving the Paris Goals of 1.5°C and 2°C without “overshoot” are out of reach

We are increasingly likely to “overshoot” average global temperatures of 1.5°C and 2°C (meaning that global average temperature temporarily (on order of decades) exceeds the temperature target before reducing again. This can only occur if atmospheric GHG concentrations are lowered – and this is through carbon dioxide removal (CDR), which is by no means a given (see below)). Growing research shows that, for the same end of century temperature increase, overshooting is likely to lead to more climate damages (some of which are irreversible) – like biodiversity loss and extreme weather – than if we get there with no overshoot 4Zickfeld, K. and Herrington, T., 2015. and; Ricke, Katharine L., and Caldeira, K., 2014 and; Tachiiri, K., Hajima, T. and Kawamiya, M., 2019.. 

Delaying mitigation means we will have to cut more emissions each year to stay Paris-aligned by 2030. We already knew the dangers of delayed mitigation in 2014, when the IPCC stated that scenarios with high emissions through to 2030 would have higher long-term economic costs, and would “substantially increase the difficulty of the transition” and “narrow the range of options consistent with… 2°C”. Today, average annual emissions cuts needed to stay below 1.5°C are four times higher than they would have been if collective mitigation and ambition started in 2010, according to UNEP. This highlights the need to act fast.

Investment levels are also nowhere near to what we need to stay Paris aligned. The 2015 Paris Agreement recognised the key role finance plays in both mitigation and adaptation – it placed investors and financial commitments centre stage for climate policy and action. However, climate finance has only increased slightly since AR5, reaching about USD 579 billion in 2018/2017. This is about ten times less than the estimated USD 6.3 trillion needed every year by 2030 to stay Paris aligned. 

Since AR5, the split between public and private climate finance has remained relatively stable (about 44% public and 56% private in 2018). Private finance has, however, outpaced public finance in the energy sector, and increasingly so in transport, reflecting a more mature renewable energy market and the fact that projects are now perceived to be less risky. The private sector is expressing increasing concern over the risks of climate impacts, but climate-related financial risks remain underestimated by financial institutions and decision makers 5Some disclosure measures, like the Task Force on Climate-Related Financial Disclosure (TCFD) may also be largely ineffective, as the assumption that transparency will automatically lead investors to ‘rationally’ respond by moving climate finance from high- to low-carbon assets could be oversimplified..

3. The richest 1% emit more than twice the poorest 50%

Since AR5, there has been increased interest in the ‘national responsibility’ for climate change, as well as the links to other sustainability, development and social issues. The US is responsible for about 20% of cumulative historical emissions, followed by China, Russia, Brazil and Indonesia. Just looking at national emissions does not, however, complete the picture, as the unequal size, wealth and carbon intensity of populations need to be factored in. Looking at emissions relative to population size, developing countries tend to have lower per-capita emissions and, if emissions are normalised to population, China, Brazil and Indonesia do not even make the top 20. 

The richest 1% worldwide emit more than twice the combined share of the poorest 50%, according to UNEP. Activities that emit a lot, but only benefit a few, include flying and driving SUVs. For example, if emissions from SUVs were counted as a nation, it would rank 7th in the world. As COVID-19 caused carbon emissions to fall last year, the SUV sector continued to see emissions rise. In 2018, only 2% to 4% of people got on an international flight, and 1% of the global population are responsible for about half of CO2 emitted from all commercial flights. The aviation industry is responsible for 2.4% of global emission, as such these 1% users could be contributing about 450 million tonnes of CO2 each year – about the same as South Africa’s annual emissions. 

Research, including last month’s landmark AR6 WGII report, shows that climate change affects people differently by gender, race and ethnicity, and these all link to economic vulnerability. Marginalised groups have less access to energy, and use less. For example, women’s carbon footprints are generally lower than men’s, mostly due to reduced meat consumption and driving, though this varies across nations 6See reference 1, 2 and 3. But, even though women generally emit less, their inclusion in policy making can lead to better climate policy. Climate groups are now recognising that disadvantage is the result of many interacting systems of oppression.

4. But there is hope: since AR5 national and corporate net-zero commitments have exploded and renewable energy has continued to outperform forecasts

Since AR5, there has been a substantial growth in climate policy, legislation and treaties at both international, national and sub-national levels. Most importantly, in 2015, the Paris Agreement was signed. The Paris Agreement Article 4 seeks to achieve a “balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases”, which can be interpreted as net zero greenhouse gas emissions (not just CO2). Renewable energy has also continued to massively outperform forecasts, making it a post-AR5 success story. Just in 2020, the amount of new renewable electricity capacity added rose by 45% to 280 gigawatts, the largest year-on-year increase since 1999 (more in box below), while costs have fallen sharply in that time. And, more recently, the concept of ‘net-zero’ entered the policy arena in full force. 

In 2014, the IPCC was not directly using net-zero language, but concluded that limiting the cumulative emissions of GHGs to zero was key to stopping climate change. In 2018, the IPCC outlined that to limit warming to 1.5°C, CO2 emissions would need to fall by about 45% in 2030 (relative to 2010 levels), and global net-zero had to be reached around 2050. WG1 of AR6 (released in August 2021) outlined the need not only for a cut in CO2 emissions, but also strong reductions in other GHGs 7IPCC AR6 WGI D.1. In 2019, the UK became the first G7 economy to legislate for net-zero. Today, 136 countries with 85% of the world’s population, covering 88% of global emissions have set net zero targets, although the targets and timing of how they are delivered remain under criticism for being too vague. This 2021 paper sets out ways that governments could begin to add clarity and accountability; issues considered key to delivering net zero GHG emissions, in pursuit of the Paris targets.

What does achieving net-zero actually look like?

There are many scenarios assessing how we can get to net-zero, and we await the IPCC’s assessment to get an up-to-date, global view. However, some of the key points likely to appear are summarised here. 

Achieving the Paris goals requires rapid mitigation across the full range of GHGs. Scientists have shown that, even if CO2 emissions are Paris-aligned, ignoring methane emissions will lead to overshooting the Paris agreed temperature goals, while abating N2O emissions would help achieve the temperature targets as well as a suite of Sustainable Development Goals (SDGs). 

Renewable electrification is key. A consistent success story since AR5 is the rapid deployment and falling costs of Renewable Energy (RE), such as solar, wind and batteries, which have massively outpaced and exceeded the expert expectations outlined in AR5. But we still need to ramp up. The amount of solar PV and wind deployment has to be twice what has already been announced globally to stay on a 1.5°C trajectory, according to the IEA. We also need to boost funding to clean energy solutions, as many of the technologies needed for hard-to-abate sectors are still in development and annual investment into clean energy needs to triple to USD 3.6 trillion through 2030. 

Fossil fuel use needs to decline dramatically. Global coal emissions needed to have peaked in 2020, and all coal-fired power plants need to be shut by 2040 at the latest, a Climate Analytics analysis based on the IPCC’s 2018 report shows. For OECD nations, all coal use should be phased out by 2031. This was echoed by the IEA in 2021 – it concluded that for net-zero, all unabated coal and oil power plants need to be phased out by 2040. Increasing energy efficiency is also key. In the IEA’s net-zero compliant scenario, the energy intensity of the global economy decreases by 4% a year between 2020 and 2030 – more than double the average rate of the last decade.  

Some degree of carbon removal is needed. Net-zero is achieved when the emissions going into the atmosphere are balanced by those removed. It is possible to achieve global net-zero while still allowing for emissions in some sectors – as long as these ‘hard to abate’ emissions are also being removed and permanently stored. Methods of removal range from enhancing natural carbon drawdown through reforestation, restoration and the protection of nature, to ‘negative emissions technology’ like direct air capture (DAC) and bioenergy with carbon capture and storage (BECCS). In the last few years, more attention has been paid to the ‘net’ part of net-zero, as pretty much all published scenarios that bring us within 1.5°C or 2.0°C rely on some form of CDR. 

Transforming the Agriculture, Forestry and Other Land Use (AFOLU) sector is crucial. Today, it accounts for nearly a quarter of global GHG emissions and sectoral emissions have been climbing in recent years. Livestock production and rice cultivation are the main culprits. The sector is also a carbon sink, as plants and biomass draw CO2 from the atmosphere when they grow. Transforming the sector can both reduce emissions – for example, by changing farming and livestock methods – as well as remove emissions from the atmosphere, including measures like planting more (and protecting existing) forests. However, reforestation and better land management alone will not be enough. Some estimates suggest that transforming the AFOLU sector could at most account for 30% of the mitigation needed to stay below 1.5°C. However, the recent hype that planting trees and investing in land can solve the climate crisis is risking delayed mitigation and greenwashing.

Urban planning needs to consider carbon emissions from the get go. The current scale and speed of urbanisation is unprecedented in human history, and since AR5 it has become even more clear that urban areas contribute the majority (about 70%) of the global footprint, posing an enormous challenge for climate mitigation. New urban planning presents a unique opportunity to reduce carbon lock-in. 

Many more aspects of mitigation and gaps in our knowledge will be explored by the IPCC in this report. For example, the IPCC will dedicate a chapter to demand-side mitigation for the first time, which will explore how behaviour and lifestyle changes can reduce emissions, like shifts in diets, transport, buildings and the efficient use of materials and energy. In general, scientists agree that systemic infrastructural and behavioral change will be part of the transition to a low-carbon society, but the feasibility and mitigation potential of demand-side measures remain a knowledge gap.

5. Looking ahead, transparency is key

Net-zero targets should not be seen as end-points, but rather as milestones on the path to negative emissions, milestones that require detailed roadmaps as well as short-term goals. NGOs, scientists and the public continue to demand mitigation plans and net-zero targets that are clear and transparent, asking policymakers, businesses and financiers to clarify the scope, fairness and approach to decarbonisation. 

Over the past years, integrated assessment models (IAMs) have been a critical tool for climate policymakers, but they have also come under intense scrutiny due to issues like the huge reliance on CDR, especially BECCS, in many scenarios. However, over reliance on IAMs have been criticised given its opaque design and economic assumptions which can result in modelling outcomes that overemphasise CDR. 

In a 2020 paper, the co-chairs of the upcoming WGIII report outlined how the IPCC has taken steps to increase transparency this time around. They said the new report will contain some notable criticisms of IAMs, including the uncertainties, CDR and limits to land. It is, however, important to note that the IPCC itself is not advocating for any scenarios, including those with large amounts of CDR. Instead, the IPCC findings are a reflection of the state of climate modelling, as well as previous emissions pathways and scenario research.

Is it possible to stay Paris aligned without carbon removal?

Many of the scenarios used in earlier IPCC reports (including the special report on 1.5C) relied heavily on negative emissions in the second half of the century. Modelled negative emissions were primarily achieved by inputting a large amount of BECCS and/or forest protection/planting in the future scenarios. 

The numbers for future CDR are often huge, though they vary across models and scenarios. For example, in the IPCC’s special report on 1.5°C, the cumulative carbon removal needed by the end of the century was estimated to be somewhere between 100 and 1000 billion tonnes of CO2. For perspective, we emit more than 40 billion tonnes a year now, so even in the very lowest scenario we would have to remove more than two years’ worth of global CO2 emissions. 

Academics and NGOs have also pointed to the fact that all methods of carbon removal come with side effects and trade-offs that are context and method dependent – such as the huge land areas needed for BECCS, or energy requirements for Direct Air Capture with Carbon Storage (DACCS) (a technology  which some scientist predict could remove tens of GtCO2 by the end of century). Land-based carbon removals also come with other trade-offs, such as increased competition for agricultural land and disruption of biodiversity. There has also recently been an increased recognition that unrealistically high carbon removal projections could be encouraging delayed action and greenwashing. 

In this report, the IPCC intends to explain the limitations and trade-offs of carbon removal carefully, while assessing the amount of CDR in many of the scenarios. There has also been a new wave of scientific literature looking at how to achieve the Paris goals with no carbon removal whatsoever. These pathways show us that net-zero without the ‘net’ (let’s call it ‘true zero’) requires much more rapid transformations of the energy system and larger near-term emissions cuts. These scenarios also lead to multiple other benefits (so-called ‘co-benefits’) like avoiding drastic land-use change, as well as benefiting food systems, biodiversity and the environment in the long-term.

6. Further reading and academic papers

1. Since AR5 greenhouse gas emissions have continued to climb

Explainers and reports 

Selected academic research studies and reviews  

2. A lack of ambitious mitigation has made us increasingly likely to ‘overshoot’ the Paris Goals of 1.5°C and 2°C.

Explainers and reports 

Selected academic research studies and reviews  

3. The richest 1% emit more than twice the poorest 50% 

Explainers and reports 

Selected academic research studies and reviews  

4. But there is hope: since AR5 national and corporate net-zero commitments have exploded and renewable energy has continued to outperform forecasts

Explainers and reports 

Selected academic research studies and reviews  

5. Looking ahead, transparency is key  

Explainers and reports 

Selected academic research studies and reviews  

  • 1
    WGIII will be third of  four separate reports published in the AR6 cycle. ‘The Physical Science Basis’ which detailed the current state of the climate was published on 9 August 2021 and the second report ‘impacts, adaptation and vulnerability’ was released in March 2022.
  • 2
    These numbers are based on pre-Glasgow estimates. If you add all pre-Glasgow net-zero pledges to the NDCs this brings the world on track for 2.2°C, according to UNEP (or about 2.1°C in IEA assessments), page 12, section 7 of the 2021 Emissions Gap Executive Summary.
  • 3
    Most recent estimates show that only 440 Gt CO2 is left from 2020 to stand even a 50% chance of 1.5°C. Global emissions were over 40 Gt CO2 in 2019, and if annual emissions are similar in the next decade it will be used up in the 2030s.
  • 4
    Zickfeld, K. and Herrington, T., 2015. and; Ricke, Katharine L., and Caldeira, K., 2014 and; Tachiiri, K., Hajima, T. and Kawamiya, M., 2019.
  • 5
    Some disclosure measures, like the Task Force on Climate-Related Financial Disclosure (TCFD) may also be largely ineffective, as the assumption that transparency will automatically lead investors to ‘rationally’ respond by moving climate finance from high- to low-carbon assets could be oversimplified.
  • 6
    See reference 1, 2 and 3
  • 7
    IPCC AR6 WGI D.1

IPCC WGIII report: The land sector and climate mitigation

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This briefing summarises the Working Group III (WG3) of the IPCC’s main insights about the mitigation options with the Agriculture, Forestry and Other Land Uses (AFOLU) sector. The term “land sector” will be used throughout this briefing for clarity. The briefing also summarises the findings on the needs and limitations of land-based carbon dioxide removal (CDR).

Key points

  • Rapid deployment of mitigation in the land sector is essential in all 1.5°C pathways. It can provide up to 30% of the global mitigation needed for 1.5°C and 2°C pathways.
  • The sector offers significant near-term mitigation potential at relatively low cost. The global land-based mitigation potential is ~8–14 billion tonnes of CO2 equivalent (GtCO2-eq) each year between 2020-2050. About 30-50% of this potential could be achieved under USD20 per tCO2-eq. Options costing USD100 per tCO2-eq or less could reduce global GHG emissions by at least half the 2019 level by 2030 (SPM C.12). But land-based mitigation cannot compensate for delayed emissions reductions in other sectors.
  • The IPCC recognises that carbon dioxide removal (CDR) is necessary to achieve net-zero GHG globally. Modelled scenarios rely heavily on forest planting and BECCs as main options to remove emissions from the atmosphere to achieve it. 
  • But, the IPCC is not advocating for large-scale CDR. There are many uncertainties, risks and a lack of social licence for these options. It is still uncertain whether CDR through some land-based measures can be maintained in the very long term because sinks can saturate, for example. CDR cannot be deployed arbitrarily and given the time needed to ramp-up CDR, it can only make a limited contribution to reaching net zero in the timeframe required.
  • There is a substantial investment gap in the sector. The IPCC estimates that, to date, only USD 0.7 billion a year has been invested in land-based mitigation, well short of the more than USD 400 billion per year needed to deliver the up to 30% of global mitigation effort in deep mitigation scenarios.

The land sector is key to climate mitigation, but only within limits

The land sector is both a carbon source and a carbon sink. It accounted for ~13%-21% of global greenhouse gas (GHG) emissions between 2010-2019. 1Chapter 7, p.4. This is different from emissions of the entire food system, which are estimated to account for  23-42% of global GHG emissions in 2018 – Ch.12, p.4. For sinks there is also a error of aprox +/- 5.2 But the land sector is also a carbon sink, as it draws CO2 from the atmosphere when plants grow (through the process of photosynthesis). When the sector’s sources and sinks are added up, the land sector is considered a net sink of emissions – removing about 6.6 GtCO2 a year for the period of 2010-2019. 2Chapter 7, p.4. This is different from emissions of the entire food system, which are estimated to account for  23-42% of global GHG emissions in 2018 – Ch.12, p.4. For sinks there is also a error of aprox +/- 5.2. Chapter 3, p.42 : But there are still large uncertainties on net CO2 human emissions and its long-term trends. Currently, national GHG inventories (NGHGI) tend to overestimate the amount of CO2 absorbed by sinks when compared to other global models. There is a gap of ~5.5 GtCO2 a year between NGHGI and Bookkeeping models and dynamic global vegetation models. The difference largely results from different definitions of what “anthropogenic” means, which leads NGHGIs to estimate that more CO2 is taken up by sinks.

The IPCC clearly states that the land sector has huge potential for mitigation. It can both reduce emissions – for example by changing farming and livestock practices – as well as remove them from the atmosphere, via measures like planting more forests and protecting existing ones. But the sector “cannot fully compensate for delayed action in other sectors”. (SPM C.9)

Overall, the IPCC estimates that the global land-based mitigation potential is ~8–14 billion tonnes of CO2 equivalent (GtCO2-eq) each year between 2020-2050, at costs below USD 100/tCO2. 3Chapter 7, p.41. The bottom end represents the mean from IAMs and the upper end the mean estimate from global sectoral studies. The economic potential is about half of the technical potential from AFOLU, and about 30-50% could be achieved under USD20 tCO2-eq-1. Note that the IPCC uses a different methodology for individual AFOLU options than for the total sector potential. These estimates are slightly higher than those in AR5. Considering both integrated assessment models (IAMs) and sectoral economic potential estimates, WG3 states that “land-based mitigation could have the capacity to make the sector net-negative GHG emissions from 2036 although there are highly variable mitigation strategies for how [its] potential can be deployed for achieving climate targets”. 4Chapter 7, p.42. “Economic mitigation potential is the mitigation estimated to be possible at an annual cost of up to USD100 tCO2 -1 mitigated. This cost is the price at which society is willing to pay for mitigation and is used as a proxy to estimate the proportion of technical mitigation potential that could realistically be implemented.” There are many options that can help reduce and remove emissions (Box 1). Most of the options to reduce emissions are available and ready to deploy, whereas CDR needs more investment. 5Chapter 7. 42

The IPCC does not use the term ‘nature-based solutions’ (NbS), but ‘land-based mitigation measures’. When evaluating the mitigation potential within the sector, it discusses 20 measures, both supply and demand-side (Box 1). However, when it analyses mitigation pathways, it only includes a few options because of how climate models are currently built (see the role of CDR in mitigation pathways section for more detail).

Box 1. What are the main ways the land sector reduces and removes emissions between 2020-2050? 

Forests and other ecosystems have the highest potential for carbon mitigation, according to global sectoral models. Protecting, managing and restoring these ecosystems is likely to reduce and/or sequester up to 7.4 billion tonnes of CO2 equivalent each year between 2020 and 2050. 6SPM, p.43 Crucially, the IPCC finds that protecting ecosystems has the highest potential. The report also stresses that halting deforestation and restoring peatlands is vital to keeping temperature rises below 2C. 

Agriculture and demand-side measures provide the second and third highest potential for mitigation, potentially reducing and/or sequestering up to 4.1 and 3.6 billion tonnes of CO2 equivalent a year respectively between 2020 and 2050. 7SPM, p.43 For agriculture, the measures that have the greatest potential are soil carbon management in croplands and grasslands, agroforestry, biochar and rice cultivation, as well as livestock and nutrient management. On the demand-side, it’s shifting to healthy diets and reducing food waste and loss.

Land sector mitigation measures can have important co-benefits, but only if done properly. For example, “reforestation and forest conservation, avoided deforestation and restoration and conservation of natural ecosystems and biodiversity, improved sustainable forest management, agroforestry, soil carbon management and options that reduce CH4 and N2O emissions in agriculture from livestock and soil, can have multiple synergies with the sustainable development goals.” 8SPM, p. 53

But there are many risks and trade-offs. Large-scale or poorly planned deployment of bioenergy, biochar, and afforestation of naturally unforested land. (high confidence) for instance, can compete with scarce resources, such as agricultural land. 9SPM, p. 55 This can threaten food production and security and reduce adaptive capacity. The use of non-native species and monocultures (e.g. planting one type of tree) in forest projects can also lead to biodiversity loss, and negatively impact ecosystems. 10Chapter 7 of WGIII provides an overview of 20 mitigation measures, evaluating the co-benefits and risks from land-based mitigation measures, estimated global and regional mitigation potential and associated costs according to literature published over the last decade. There are also risks in relation to land’s ability to continue to act as a carbon sink in the future, which can reduce land sector measures’ capacity to mitigate emissions. 11Chapter 7.4

Joint and rapid effort is key to achieving high levels of mitigation in the sector, the IPCC says. But there has been a lack of funds to support these efforts. The IPCC estimates that, to date, only USD 0.7 billion a year has been invested in the sector, well short of the more than USD 400 billion per year needed to deliver the up to 30% of global mitigation effort envisaged in deep mitigation scenarios.12Chapter 7, p.6. This is based on land-based carbon offsets (i.e. money from the Clean Development Mechanism, voluntary carbon standards, compliance markets and reduced deforestation).

What does the IPCC say about the scale of land-based CDR?

Mitigation potential of different CDR options

CDR is defined by the IPCC as “human activities that remove emissions from the atmosphere and durably store it”. Thus, CDR excludes uptake of emissions not directly caused by humans. CDR can help in several phases of mitigation: 

  1. Reducing net CO2 or GHG emission levels in the near-term 
  2. Counterbalancing residual emissions from hard-to-transition sectors like industry and agriculture to help reach net-zero CO2 or GHG emissions targets in the mid-term 
  3. Achieving and sustaining net-negative CO2 or GHG emissions in the long-term if deployed at levels exceeding annual residual emissions. 13SPM, p. 48 Therefore, offsets are discussed in the report as a way to counterbalance residual emissions, highlighting that hard-to-abate sectors could have more social licence to rely on CDR. 14The IPCC evaluates previous offsets measures, such as REDD+, offsets within emissions trading systems, among others in chapter 7;Chapter 3, p. 14-15

Currently, the only widely practised CDR methods include afforestation, reforestation, improved forest management, agroforestry and soil carbon sequestration. 15SPM, p. 47 Figure 1 presents the options that can be deployed on land as well as in the oceans. The IPCC discusses these options, presenting a summary of their mitigation potential, risks, co-benefits and costs. (Table 1 in the appendix)  However, the IPCC does not go into detail on all options. For example, it mentions that the choice of feedstock for BECCS could lead to positive or negative impacts, but does not explore all feedstock options and their related consequences.

Figure 1. CDR methods across Land sector and Oceans (​​IPCC- WG3 Chapter 12, p.37)
The role of CDR in mitigation pathways

The WG3 report looks at what the science says about mitigating the climate crisis. As established in most scientific literature, achieving net zero by mid-century is the safest way to stay Paris aligned. There are, however, many different routes to net zero. Thus, the scope of this report is to chart the options, limits, benefits and trade-offs of pursuing a net-zero emissions society. To do this, the IPCC reviewed more than 3000 pathways, including over 1200 scenarios, to develop five “Illustrative Mitigation Pathways” (IMPs) and two high-emissions pathways for reference.

The report finds that “CDR is a necessary element to achieve net-zero CO2 and GHG emissions, and counterbalance residual emissions from hard-to abate sectors”. 16Chapter 12, p. 35 It is also a key element in scenarios that are likely to limit warming to 2°C or lower by 2100”. 17Chapter 12, p. 35 All of its IMPs use land-based CDR, which is dominated by BECCS, afforestation and reforestation. 18Chapter 12, p.4 and p. 55

In most scenarios that limit temperatures to 2°C or lower, the IPCC predicts cumulative volumes of CO2 removed between 2020-2100 could reach (all median values): 19Chapter 12, p. 5

  • BECCS – 328 GtCO2 
  • Net CO2 removal on managed land (including afforestation and reforestation) – 252 GtCO2
  • Direct Air Capture Capture and Storage (DACCS) – 29 GtCO2

To put this into perspective, the remaining carbon budget assessed by WG1 from the beginning of 2020 onwards is 500 GtCO2 for limiting warming to 1.5°C with a 50% chance of success. 20Summary for policymakers, p. 6 The IPCC also predicts that mitigation measures in 2°C or below pathways can significantly transform land all around the world. These pathways are “projected to reach net-zero CO2 emissions in the land sector between the 2020s and 2070, with an increase in forest cover of about 322 million hectares (-67 to 890 million ha) [an area almost as big as the US and India combined] in 2050 in pathways limiting warming to 1.5°C with no or limited overshoot”. 21Chapter 3, p. 6

Delaying action will result in larger and more rapid deployment of CDR later, especially if there is a temperature overshoot. Then, large-scale deployment of CDR will be needed to bring temperatures back. 22Smith et al. 2019; Hasegawa et al. 2021 Since IAM pathways rely on afforestation, reforestation and BECCS, delayed mitigation can lead to a lot of changes in land use, with negative impacts for sustainable development. 23IPCC 2019, Hasegawa et al. 2021  The IPCC points out that “strong near-term mitigation to limit overshoot, and deployment of other CDR methods than afforestation / reforestation and BECCS may significantly reduce the contribution of these CDR methods in scenarios limiting warming to 1.5 or 2C”. 24Chapter 12, p. 56 “Stronger focus on demand-side mitigation implies less dependence on CDR and, consequently reduces pressure on land and biodiversity”. 25Chapter 3, p. 7  It adds that: “Within ambitious mitigation strategies…, CDR cannot serve as a substitute for deep emissions reductions”. 26Chapter 12, p. 38 To put this into perspective, the market for carbon offsets today, which include these CDR measures, reduce global emissions by about 0.1%, according to the Energy Transitions Commission.

But while most scenarios in WG3 still rely on CDR to achieve net-zero, the IPCC is not advocating for large amounts of it. Instead, the reliance on CDR reflects the state of climate modelling and research (see box 2 in appendix). The IPCC discusses the uncertainty, risks and lack of social licence for CDR, such as concerns that large-scale CDR could obstruct near-term emission reduction efforts or lead to an over-reliance on technologies that are still in their infancy. 27Chapter 12, p. 39 It stresses that there is uncertainty about how much CDR will be deployed in the future and the amount of CO2 it can remove permanently from the atmosphere. 28Chapter 12, p. 39 This is because some measures in the land sector cannot be maintained indefinitely as these sinks will ultimately saturate, while trees can also be cut down, burnt or die prematurely. 29Chapter 3, p.7

Box 2. A word about climate models and the potential and limitations of land sector mitigation 

Since the last IPCC reports, there have been more assessments of the total mitigation potential of the land sector. 30Chapter 7, p.40 These can be split into:

  • Sectoral models: These estimate the potential of the sectors and/or individual measures. But they rarely capture cross-sector interactions, making it difficult for them to account for land competition and trade-offs. This could lead to double counting when aggregating sectoral estimates across different studies and methods. 31Chapter 7, p.40-42 They usually show higher mitigation potential as they include more land-based mitigation options than IAMs. 32Chapter 3, p. 64
  • IAMs and integrative land-use models (ILMs): IAMs assess multiple and interlinked practices across sectors, and thus account for interactions and trade-offs (i.e. land competition). IMLs combine different land-based mitigation options, which are only partially included in IAMs. Both have extended their coverage, but the modelling and analysis of land-based mitigation options is new compared to sectoral models. Consequently, “[Land sector] options are only partially included in these models, which mostly rely on afforestation, reforestation and BECCS”. 33Annex III- p.29; Chapter 7, p.86
  • Currently, most models do not consider, or have limited consideration of, the impact of future climate change on land. 34Chapter 7. 42.And there is still uncertainty about land’s ability to act as a sink in the future and how this will impact mitigation efforts. 35Chapter 7. 116  Bottom-up and non-IAM studies show significant potential for demand-side mitigation. 36Chapter 3, p. 7 (see Table 2 in the Appendix)

When evaluating the potential of different land-based mitigation measures, AR6 uses mainly sectoral models and compares to IAM’s, when available. But, AR6 still relies on IAMs/ILMs to devise mitigation pathways. This can be problematic in two main ways:

  • Climate change impacts on land and future mitigation potential: Given the IPCC WG1 finding that land sink efficiency is decreasing with climate change, relying too much on land to remove CO2 from the atmosphere could be problematic. This could create a false sense of security and allow for land mitigation to be used as an excuse for not making deep emissions cuts. This is key as many corporations are relying on offsetting emissions in the land sector instead of reducing them. 

Unrealistic CDR projections (over-reliance on BECCS and afforestation and reforestation): The volumes of future global CDR deployment assumed in IAM scenarios are large compared to current volumes of deployment. This is a challenge for scaling up. Similarly, the lack of representation of other options makes it difficult to compare different measures and envisage a different future that alters the contribution of land in terms of timing, potential and sustainability.

Appendix – Mitigation potential of different CDR measures

  • 1
    Chapter 7, p.4. This is different from emissions of the entire food system, which are estimated to account for  23-42% of global GHG emissions in 2018 – Ch.12, p.4. For sinks there is also a error of aprox +/- 5.2
  • 2
    Chapter 7, p.4. This is different from emissions of the entire food system, which are estimated to account for  23-42% of global GHG emissions in 2018 – Ch.12, p.4. For sinks there is also a error of aprox +/- 5.2. Chapter 3, p.42 : But there are still large uncertainties on net CO2 human emissions and its long-term trends. Currently, national GHG inventories (NGHGI) tend to overestimate the amount of CO2 absorbed by sinks when compared to other global models. There is a gap of ~5.5 GtCO2 a year between NGHGI and Bookkeeping models and dynamic global vegetation models. The difference largely results from different definitions of what “anthropogenic” means, which leads NGHGIs to estimate that more CO2 is taken up by sinks.
  • 3
    Chapter 7, p.41. The bottom end represents the mean from IAMs and the upper end the mean estimate from global sectoral studies. The economic potential is about half of the technical potential from AFOLU, and about 30-50% could be achieved under USD20 tCO2-eq-1. Note that the IPCC uses a different methodology for individual AFOLU options than for the total sector potential.
  • 4
    Chapter 7, p.42. “Economic mitigation potential is the mitigation estimated to be possible at an annual cost of up to USD100 tCO2 -1 mitigated. This cost is the price at which society is willing to pay for mitigation and is used as a proxy to estimate the proportion of technical mitigation potential that could realistically be implemented.”
  • 5
    Chapter 7. 42
  • 6
    SPM, p.43
  • 7
    SPM, p.43
  • 8
    SPM, p. 53
  • 9
    SPM, p. 55
  • 10
    Chapter 7 of WGIII provides an overview of 20 mitigation measures, evaluating the co-benefits and risks from land-based mitigation measures, estimated global and regional mitigation potential and associated costs according to literature published over the last decade.
  • 11
    Chapter 7.4
  • 12
    Chapter 7, p.6. This is based on land-based carbon offsets (i.e. money from the Clean Development Mechanism, voluntary carbon standards, compliance markets and reduced deforestation).
  • 13
    SPM, p. 48
  • 14
    The IPCC evaluates previous offsets measures, such as REDD+, offsets within emissions trading systems, among others in chapter 7;Chapter 3, p. 14-15
  • 15
    SPM, p. 47
  • 16
    Chapter 12, p. 35
  • 17
    Chapter 12, p. 35
  • 18
    Chapter 12, p.4 and p. 55
  • 19
    Chapter 12, p. 5
  • 20
    Summary for policymakers, p. 6
  • 21
    Chapter 3, p. 6
  • 22
  • 23
  • 24
    Chapter 12, p. 56
  • 25
    Chapter 3, p. 7
  • 26
    Chapter 12, p. 38
  • 27
    Chapter 12, p. 39
  • 28
    Chapter 12, p. 3
  • 29
    Chapter 3, p.7
  • 30
    Chapter 7, p.40
  • 31
    Chapter 7, p.40-42
  • 32
    Chapter 3, p. 64
  • 33
    Annex III- p.29; Chapter 7, p.86
  • 34
    Chapter 7. 42
  • 35
    Chapter 7. 116
  • 36
    Chapter 3, p. 7

Reducing methane emissions is key to the climate fight

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With the upcoming IPCC WGI report set to include a chapter on short-lived climate forcers for the first time, this briefing asks why are methane emissions so important to climate change?

Human greenhouse gas (GHG) emissions are driving climate change. Since the pre-industrial period, these emissions have caused all of the earth’s observed warming, with carbon dioxide (CO2) responsible for the majority of it. After CO2, methane (CH4) is the biggest contributor to climate change. The new IPCC report (working group 1 of AR6) is likely to focus on the role of methane in driving climate change. 

Methane emissions are a huge problem because while the gas only stays in the atmosphere for about nine years, it has 28 times more warming power than carbon dioxide over 100 years. Methane concentrations are increasing faster now than at any time since the 1980s, reaching more than two-and-a-half times pre-industrial levels. This is well above the safe limits outlined by the IPCC in AR5. Methane is now responsible for almost a quarter of warming, bringing us closer to breaching the 1.5°C temperature target. Cutting human-caused methane emissions is one of the most cost-effective ways to rapidly reduce the rate of warming and limit temperature rise to 1.5°C.

What are the key emitting sectors and mitigation opportunities?

Methane emissions come from natural sources, such as wetlands, but more than half of total global methane emissions come from human activities. Three sectors – agriculture (40% of human-caused emissions), fossil fuels (35%) and waste (20%) account for the majority of human methane emissions. Almost a third (32%) of agricultural methane emissions come from livestock production 1 Estimating methane emissions is an ongoing topic of research, particular in the livestock sector as the amount of methane emitted depends on many factors, such as the number of animals or the type of feed consumed.. Oil and gas extraction, processing and distribution account for 23% of methane emissions in the fossil fuel sector and coal mining accounts for 12% of emissions. Landfills and wastewater comprise 20% of methane emissions in the waste sector. 

Many cost-effective mitigation measures are readily available, such as reducing emissions that escape  along the natural gas supply-chain, better treatment of solid waste, and improving livestock and crop management (see table below for some examples). Mitigation options across the three sectors represent some of the best levers to reduce warming and its climate impacts over the next 30 years. In particular, the fossil fuel industry has the greatest potential for methane cuts by 2030, according to the UN – up to 80% of oil and gas measures and up to 98% of coal measures could be implemented at negative or low cost. But action across all three sectors is needed to ensure emissions are in line with 1.5ºC. All together, cutting methane  in those three sectors could reduce human methane emissions by 45% by 2030. This would avoid nearly 0.3°C of global warming by the 2040s, helping to keep temperatures below 1.5ºC while preventing 255,000 premature deaths and 26 million tonnes of crop losses globally.

Policy measures to reduce methane emissions in top three emitting sectors
Source: Global Methane Assessment, 2021; IPCC SRCCL report 2019 – chapter 6.

Methane and Agriculture: An overlooked problem

Most methane emissions (32%) from agriculture come from raising livestock via enteric fermentation – a ruminant animal’s natural digestive process – and manure. Other key agricultural sources are landfills, waste and rice cultivation. The upcoming IPCC AR6 report is expected to confirm the link between livestock production and increased methane emissions. 

While countries recognise agriculture as a source of methane emissions, most do not take concrete action to cut them. In fact, methane emissions from agriculture are expected to continue to grow as demand for meat increases, particularly in low and middle-income countries. 
Given agriculture’s huge footprint, actions to reduce methane emissions in the sector are key for reaching climate targets. A robust evidence base indicates that reduced food waste and loss, improved livestock management, and eating fewer animal products could reduce emissions by 65–80 million tonnes a year over the next few decades 2In the livestock sector, options differ between production systems. For example, improving management via feed additives, vaccines can reduce enteric fermentation in more intensive systems, such as dairy in the US. Manure management is more applicable in farms where manure can be easily collected, such as in smallholder, mixed crop-livestock systems.. Widespread adoption of such measures could bring anthropogenic methane emissions in line with those in 1.5ºC scenarios. But, governments should carefully choose policies because some models show that achieving very low emissions per kilogram of protein involves large-scale industrialised agriculture. This is problematic as adopting industrial agriculture methods come with many social and environmental impacts that are not captured in models and can increase GHG emissions. If these were accounted for, industrial agriculture would put the 1.5ºC target out of reach. Farming systems that shift away from industrial agriculture, such as agroforestry and organic farming, not only help to reduce emissions of all GHG, but also improve farmers’ livelihoods, food security and biodiversity.

What have governments done to reduce methane emissions?

Now more than ever, global action on methane emissions is needed. But governments have often failed to cut emissions, partly due to a lack of reliable emissions data and reporting from the industries themselves. Meanwhile, countries’ climate targets – known as nationally determined contributions (NDCs) – only address methane in general terms, without a clear target or strategies to reduce emissions. Only nine of the 174 countries that have submitted NDCs set a separate target for methane emissions. Lack of measurable targets to abate methane emissions is apparent especially in the agricultural sector. Close to 80% of countries (148 out of 189) that have submitted NDCs include agriculture, but NDC targets are vague. Most (128 out of 148 countries or 86%) include the sector in overall economic or broader targets and do not elaborate on concrete actions to reduce emissions from farming. Very few also set targets in relation to other parts of the food system that emit methane, such as adopting sustainable diets. As a result, the potential to reduce global emissions of methane remains largely untapped.

Decarbonisation strategies without methane-specific policies are insufficient to keep warming below 1.5ºC . These strategies – which target carbon dioxide –  only achieve about 30% of the methane reductions needed over the next 30 years in a 2ºC scenario, for example. Moreover, cutting methane emissions now is more cost effective as mitigation costs increase with delayed action. If countries abate methane emissions by 2030, costs could be less than USD 600 per tonne of methane, especially in the waste and coal sectors in most regions. In 2050, costs could be roughly 50% higher than 2030. At the same time, without relying on future, massive-scale deployment of unproven carbon removal technologies, expansion of natural gas infrastructure and current levels of livestock farming is incompatible with keeping warming to 1.5°C.

Resources

  • 1
     Estimating methane emissions is an ongoing topic of research, particular in the livestock sector as the amount of methane emitted depends on many factors, such as the number of animals or the type of feed consumed.
  • 2
    In the livestock sector, options differ between production systems. For example, improving management via feed additives, vaccines can reduce enteric fermentation in more intensive systems, such as dairy in the US. Manure management is more applicable in farms where manure can be easily collected, such as in smallholder, mixed crop-livestock systems.

IPCC’s upcoming 6th Assessment Report: Physical Science

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The Intergovernmental Panel on Climate Change (IPCC) – the UN body responsible for climate science – is releasing the first of its three-part 6th Assessment Report (AR6) on 9 August, after a virtual plenary held between 26 July and 6 August. This will be an important media moment. The Working Group I (AR6 WGI) report will be the biggest update of the state of knowledge on climate science since the release of AR5 in 2014, and its three recent special reports (SR1.5, SRCCL, SROCC). The reports are ratified after a plenary negotiation in which governments formally approve the summary for policymakers, ensuring high credibility in both science and policy communities. 

The AR6 assessment will consist of three separate reports. ‘The Physical Science Basis’ is the first AR6 report and will detail how the greenhouse gases (GHG) we emit are causing unprecedented damage. The outline for the first report is approved. It will cover topics like extreme weather, human attribution, the carbon budget and feedback cycles, and will chart the current and future state of the climate. 

In preparation for the release of the first AR6 report, this briefing covers some of the major climate science developments since AR5 that are relevant to the current science discourse.

1. Human influence on the climate is an established and indisputable fact

Extreme event attribution studies can also tell us if, and how, climate change made a particular extreme weather event more likely or more intense. The expanded attribution literature shows that heatwaves, droughts, tropical cyclones and compound events are directly linked to human activities. In fact, new research has shown that some extreme events would have been impossible without climate change, like the Siberian heat wave in 2020 and the extreme heat across Asia in 2016. Today, scientists can also conduct attribution studies within a few days of an event occurring. One group of scientists published a study showing climate change made the 2018 European heatwave more likely while it was still going on. Another group was able to make an event attribution forecast prior to 2018’s Hurricane Florence.

The COVID-19 pandemic reminded us how much our actions matter: during the peak of global lockdowns daily emissions dropped by 17% compared to 2019, levels not seen since 2006, and people around the world were allowed a short respite from deadly air pollution. Since then, however, emissions have been rapidly ticking up again. Research has shown that the biggest opportunity from the pandemic is not the short lockdown-triggered emissions break, which will be negligible in the long run, but the potential to now tilt the economy towards a green, sustainable, just and climate centered recovery. 

2. We are closer to important temperature targets

Since AR5, we have emitted nearly 300 billion additional tonnes of CO2, bringing us closer to crucial temperature targets. In its 2018 special report, the IPCC predicted that the 1.5°C target would be breached between 2030 and 2052 in the event that we didn’t change our trajectory. Refined methods and research has since suggested that our carbon budget, a simplified (albeit imperfect) way of assessing how much more CO2 can be released, is slightly smaller than estimated in the IPCC report – leaving only 440 Gt CO2

left from 2020 to stand even a 50% chance of 1.5°C. Global emissions were over 40 Gt CO2 in 2019, and if annual emissions are similar in the next decade, the budget will be used up in the 2030s. 

The way in which scientists measure global temperature change is also more sophisticated: AR5 based its assessment of historical warming on the UK Met Office’s global temperature dataset, HadCRUT4, now an updated version (HadCRUT5) is available for AR6. The new dataset draws on an improved record of global sea surface temperatures, benefitting from more reliable methods of measuring ocean temperatures, and the record also fills in some of the gaps in Arctic data. The Arctic is the fastest warming region on the planet, so the inclusion of this data increases historic global temperature estimates by about 0.1°C. 

Adjustments to the historic warming record may, however, not directly relate to meeting the forward-looking temperature targets of the Paris Agreement. In all previous IPCC assessments there are some scenarios that see us achieve 1.5°C, but the ability to meet this target is driven by the political will and choices of decision-makers, rather than the science itself. It is also difficult to determine at what exact point we exceed a target like 1.5°C. Research from the World Meteorological Organization states there’s a 20% chance that global temperatures could average 1.5°C or above in one of the next five years. But importantly, this should not be confused with exceeding 1.5°C as a long-term average, or breaching the Paris target. 

There has also been an increased recognition that abrupt (and sometimes irreversible) changes to the climate, often called ‘tipping-points’, are more likely to occur in a world where we overshoot 1.5°C. Risks include a destabilisation of the polar ice sheets: future sea level rise is very dependent on what happens to the Antarctic and Arctic ice sheets with destabilisation potentially causing tens of centimetres of sea level rise by the end of the century. In addition, deforestation and global warming could increase the risk of the Amazon crossing into a dry state (so-called forest dieback). Researchers have also shown that passing one tipping point could increase the likelihood of others occurring, compounding risks. 

3. New and updated models have added to our understanding of the climate 

Preliminary results from AR6’s new climate models (CMIP6) have already been picked up by the media, due to suggestions that rising CO2 levels will cause more warming than previously thought. Or, in climate science speak, that the Earth has a higher “climate sensitivity”. The Equilibrium Climate Sensitivity (ECS), defined as the warming that occurs when there is double the amount of CO2 in the atmosphere relative to preindustrial times, is a crucial number for understanding climate change. 

The ECS describes the final warming after the climate fully adjusts over hundreds of years, and was first estimated at 1.5-4.5°C over 40 years ago. In comparison, the new CMIP6 models produce ECS values between 1.8-5.6°C, but almost all scientists working on the CMIP6 project have now ruled out the highest estimates. Recent research narrowed down the range further and excluded the most extreme values, arguing that the best estimate sits somewhere between 2.6-4.5°C. 

Another metric, the Transient Climate Response to cumulative Emissions of CO2 (TCRE), which describes the initial amount of warming we can expect in the coming decades, is more directly relevant to the remaining global carbon budget agreed in Paris. Since AR5, our understanding of the TCRE has expanded, with some model results indicating that it is similar or slightly higher than previous estimates, and new research has narrowed the range by about 30%. Intense debate is ongoing about the exact sensitivity numbers (ECS & TCRE), as well as the uncertainties and how the values influence carbon budgets. 

AR6 also draws on new future scenarios, built by teams of economists, climate scientists and modellers. These ‘Shared Socioeconomic Pathways’ (SSPs) explore how global economy and society may change over the next century, allowing a wider range of possible futures and offering a broader view of “business-as-usual” than the ‘Representative Concentration Pathways’ (RCPs) in AR5. 

4. Scientists are concerned about non-CO2 greenhouse gases, especially rising levels of methane

Achieving the Paris Agreement’s goals requires rapid mitigation across the full range of greenhouse gases. Methane and nitrous oxide concentrations are now higher than at any point in the last 800,000 years.

Since the pre-industrial period, CO2 has caused most warming, followed by methane – a particular focus of research in recent years. The concentration of methane is already running well above the safe limits outlined in AR5, increasing steeply since about a decade, and some scientists have suggested that methane’s warming effect is higher than estimated in AR5 (over a 100 year period). Even though there is over 230 times more CO2 in the atmosphere, methane is responsible for almost a quarter of warming. Methane only stays in the atmosphere for about 12 years, but it has a warming potential approximately 30 times that of CO2 over a century, and almost 90 times in a 20-year period.

Human activities were responsible for 50-65% of total methane emissions between 2008-2017, with agriculture and waste contributing most to the rise (56-60%), followed by the fossil fuel industry. But estimating by exactly how much, and from where, methane emissions are increasing is a topic of continued research and debate. Both coal mining and oil and gas production have grown along with methane emissions. By looking at the “atmospheric fingerprints” (isotopes) of methane some researchers have found that the role of North American shale gas – or fracking – has been significantly underestimated. Scientists have also investigated potential natural leaks of methane, and the risk of sudden methane releases from thawing Arctic permafrost.

AR6 will also be the first IPCC assessment to dedicate a whole chapter to so-called “short-lived climate forcers”, like aerosols, particulate matter and other reactive gases (such as ozone) that exist in the atmosphere for a few hours to a few months. In contrast to CO2, mitigating these gases can have an immediate impact on temperature due to their shorter lifetime. Since in most cases their reduction could also improve air quality and save lives, this is seen as a ‘win-win’ policy option. 

5. We know more about net-zero and the potential plus pitfalls of carbon removal 

Half of global GDP is generated in regions that have set (or are debating) net-zero targets, representing over 2.6 billion people. Net-zero is a target guided by science. Studies show that the climate system will continue to warm unless we reach net-zero greenhouse gases globally. Scientists continue to demand net-zero targets that are transparent: asking for them to clarify the scope, fairness and approach. Net-zero targets are in themselves not end-points, but better understood as a milestone on the path to negative emissions and therefore require long-term roadmaps as well as short-term goals.

The refined estimates of Earth’s climate sensitivity has led to some debate about the implications for our timeline to both achieve net-zero and stay below the 1.5 or 2°C temperature targets. But the relationship between these two factors is complicated and indirect. Regardless, scientists continue to stress that the best way to mitigate and avoid the most devastating impacts of climate change is to cut emissions early on and deeply in this decade with the aim of reaching net-zero as early as possible.

So what happens after net-zero is achieved globally? Scientists generally agree that net-zero will lead to a stop in temperature rise. Though models still vary on exactly how long this will take after zero. A cessation in temperature rise, however, must not be confused with a temperature reduction. As CO2 is cumulative, the amount that is in the atmosphere when we hit net-zero will determine peak temperature, unless that CO2 is removed. And even if all emissions stop, ice sheet melting and resulting sea level rise will continue, albeit slower than if we continue warming the planet. As such, the need for adaptation policies and finance, as well as provision for Loss and Damage for poor and affected communities, will remain. 
But new research finds that rapid emissions cuts reduce our risks of ‘unprecedented rates’ of warming, which would make it harder for ecosystems and societies to adapt. As such, near term emissions cuts will bring significant benefits within our lifetimes, not just in the long run. To achieve this, however, governments and businesses need to follow ambitious near-term Paris-aligned climate plans. 

Pretty much all scenarios that bring us within 1.5°C or 2.0°C rely on some form of carbon dioxide removal (CDR). Methods of removal range from enhancing natural carbon drawdown through reforestation, restoration and the protection of nature, to “negative emissions technology” like direct air capture (DAC) and bio-energy with carbon capture and storage (BECCS). 

Our reliance on CDR is however somewhat naive, as all methods of carbon removal come with side effects and tradeoffs that are context and method dependent – such as the huge land areas needed for BECCS, or energy requirements for DAC. Delayed mitigation has increased our dependence on CDR and the simple truth is that the more carbon we emit now, the more we will rely on negative emissions to stay within our target temperatures. It is fundamentally necessary, however, to immediately protect biodiversity, ecosystems and restore nature. Not just for the climate, but also to warden the rich diversity of life on our planet and to maintain people’s livelihoods.  

Scientists have studied the so-called “overshoot scenarios”, that see emissions in the near-term compensated by carbon removal that reaches “net-negative” in the latter half of the century. They found that delayed reaction time of several climate processes means even a temporary overshoot of temperature goals will result in more climate change in comparison to no overshoot (i.e. more sea level rise, acidification of the ocean, permafrost loss or perturbation of the carbon cycle). 

In the IPCC’s most recent special report (SR1.5), only 9 out of the 222 assessed temperature pathways have no overshoot, and only 44 go over 1.5°C by less than 0.1°C (low overshoot). However, there are no IPCC scenarios that completely guarantee 1.5°C. Even the most ambitious pathways see a 66% chance of keeping global temperature rise to under 1.5°C, meaning that the chances of overshooting is a subject of continued scientific uncertainty.  

Finally, there have been several more studies looking at more invasive geoengineering approaches, like solar radiation management. Though these interventions might help to reduce temperatures immediately and regionally, some of them are seen as high risk endeavours with undesired side effects, especially on the water systems and hence food security. Solar geoengineering also brings novel, and unprecedented, social justice and political challenges. It remains to be seen how the IPCC deals with assessing these technologies. The special report on 1.5°C was the first IPCC report to separate solar geoengineering from more “mainstream” carbon removal. We suspect AR6 will continue this split. 

6. Further reading: Explainers and scientific papers 

The list below summarises some of the important commentaries and scientific papers, focusing on those published in the last two years. It is not a comprehensive review of the scientific literature; think of it as a start. To explore the specific topics further, please refer to the reference lists within these publications.

1. Human influence on the climate is an established and indisputable fact 

Explainers and reports 

Selected academic research studies and reviews  

2. We are closer to overshooting important temperature targets

Explainers and reports

Selected academic research studies and reviews  

3. New and updated models have added to our understanding of the climate 

Explainers and reports

Selected academic research studies and reviews  

4. Scientists are taking account of non-CO2 greenhouse gases

Explainers and reports

Selected academic research studies and reviews  

5. We know more about net-zero and the potential plus pitfalls of carbon removal 

Explainers and reports 

Selected academic research studies and reviews   

What does the IEA Net Zero Scenario say?

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Key points

  • The IEA is ambitious on renewables and EV uptake for the first time, projecting a huge build out of wind and solar energy by 2030. The Net Zero Scenario says clean energy technologies dominate in the future, displacing fossil fuel use substantially.  
  • Shrinking fossil fuel demand means no new oil and gas fields beyond those that are approved in 2021. Oil demand peaks in 2019, and declines 275% from 2020 to 2050. Over 60% of LNG and piped-gas demand is wiped out by 2050. Some producing oil and gas fields close prematurely in the 2030s. Only low-cost producers and producers able to transform their operational models survive low oil and gas prices, but their revenues shrink massively.
  • Over half of coal demand is destroyed by 2030, registering a 90% decline by 2050. There is no need for new coal mines or unabated coal power plants beyond 2021. All subcritical coal plants need to be phased-out by 2030.  
  • The IEA projects a slower gas phase-out in this decade. Although gas demand destruction accelerates in the 2030s, half of remaining gas is used to produce hydrogen with CCUS in 2050. 
  • The IEA puts too much faith in building up hydrogen, bioenergy, NETs and CCUS to achieve net zero by 2050, despite the uncertainty over commercial viability of these technologies. The IEA also carves a critical role for oil and gas expertise in captured CO2 and low-carbon fuels.  

Clean energy soars:

  • The scenario sees a massive expansion of solar and wind in the 2020s. Solar and wind annual additions quadruple in this decade, reaching 630 GW and 390 GW by 2030, respectively. Solar is the king of the energy sector by 2050, responsible for 20% of total energy supply. Between now and 2050, solar PV capacity increases twentyfold, and wind elevenfold. Solar and wind dominate the global electricity generation in 2050, together responsible for almost 70%. 
  • Electric vehicle (EV) sales ramp up rapidly from 5% of global car sales today to 60% in 2030. The IEA recommends all governments end all new internal combustion (ICE) vehicles that run on gasoline or diesel by 2035. From this date onwards, all new cars should be either electrified or hydrogen-powered. Annual battery production surges from 160GWh today to 6600GWh in 2030, equivalent to adding 20 gigafactories every year until 2030. EV public charging infrastructure goes up from one million stations today to 40 million 2030, requiring a USD 90 billion investment by 2030. 

A shrinking role for fossil fuels:

  • There is no need for investing in new oil and gas fields, says the scenario. As fossil fuels decline from 80% of total energy supply today to 20% in 2050, investments in new oil and gas fields as well as LNG terminals, beyond current commitments, is unnecessary. This means only a small number of low-cost oil and gas producers would be able to survive, but their revenues would shrink by 75% from 2030 onwards.
  • Oil demand peaked in 2019. Oil demand never goes back to previous levels, shrinking 20% from 90 mb/d in 2020 to 72 mb/d in 2030. By 2050, oil use is 24 mb/d, registering a 275% decline over a 30-year period. Oil prices would fall to USD 25/bbl in 2050, making it hard to justify new investments, even for low-cost producers. If all investments in producing oil fields stop now, oil output would decline by 8% annually. But the IEA’s Net Zero Scenario calls for continued investments in producing oil fields, registering a 4.5% annual decline in oil output until 2050. 
  • The IEA sees a slow gas phase-out. Gas demand declines by 55% from 3,900 bcm in 2020 to 1,750 bcm in 2050. LNG and piped gas volumes would fall by 60% and 65% respectively from now to 2050. But gas use only declines by 5% to 3700 bcm in 2030, much slower than the UN Production Gap report says. After 2030, some of the existing gas fields may be closed prematurely or shut-in temporarily, risking stranded assets. By 2050, half of remaining gas use is dedicated to hydrogen production with CCUS (see section below). 
  • No investments are needed in new coal mines or expanding existing mines, and no new unabated coal plants should be approved. Coal demand falls by 90% in the next thirty years. Coal is responsible for only 1% of total energy demand in 2050. By 2030, over half of coal use is destroyed. In coal power development, the IEA identifies several milestones to reach net-zero: Starting immediately, governments should stop approval of new unabated coal power plants and phase out all (870 GW) subcritical coal-fired power plants by 2030. Coal use in power generation sharply decreases – unabated coal-fired generation is cut by 70% in 2030 – and would be partly replaced by solid biomass to allow existing assets to continue operating. In 2050, CCUS is applied to around 80% of coal produced.

The IEA NZ transition depends in the medium term on technologies that have yet to be proven at scale – Hydrogen, CCUS and NETs. However, deployment of CCUS, NETs and biomass is in the low range of other 1.5oC scenarios. 

  • Almost 50% of the emissions reductions needed between 2030 and 2050 depend on technologies that are not commercially viable yet.
  • The IEA envisages a 3,900% increase in how much carbon we capture between 2020 and 2030, or 18,900% from 2020 to 2050. The new report expects the amount of carbon we capture each year to grow from 40 million tonnes in 2020 to 1.6 billion tonnes in 2030, increasing to 7.6 billion tonnes in 2050. This means:
    • A large role for carbon capture utilisation and storage (CCUS). By 2050, of the total carbon captured, the IEA sees about 5.2 billion tonnes of carbon being captured via CCUS each year. In real terms, this means installing CCUS facilities on 10 heavy industry plants each month from 2030 onwards. However the report is more conservative on CCUS than relevant IPCC scenarios.
    • Negative emission technologies (NETs) are needed. By 2050, the remaining 2.4 billion tonnes of carbon is captured by so-called negative emissions technologies. Of this, direct air capture (DAC) soaks up about one billion tonnes and bioenergy carbon capture and storage (BECCS) about 1.4 billion tonnes. NETs should theoretically lead to an overall subtraction of carbon from the atmosphere, and are used in the IEA scenario to ‘offset’ residual emissions. The amount of negative emissions is relatively small compared to IPCC and other 1.5oC scenarios.
  • By 2050, hydrogen grows by over 500%, with a third produced from gas with CCUS. Hydrogen production grows from less than 90 million tonnes (Mt) in 2020, to more than 200 Mt by 2030, to 530 Mt by 2050. In 2030, about half of the hydrogen is sourced from coal and natural gas with CCUS. By 2050, the amount of hydrogen produced through renewables grows to 60%, still leaving a significant role for gas in hydrogen production. The IEA acknowledges that rolling out the electrolysis capacity to make ‘green’ hydrogen is a significant challenge, as there is a lack of manufacturing capacity. 
  • The IEA advocates for scaling up infrastructure investments to carry hydrogen and captured CO2 emissions. It says that annual investments for CO2 pipelines and hydrogen-enabling infrastructure have to ramp up from USD 1 billion today to USD 40 billion in 2030. This means repurposing existing gas pipelines and ships to transport hydrogen and captured CO2, which the report highlights are well matched with the oil and gas industry’s experience and skills. 
  • CCUS, in particular, is the achilles heel of the Net Zero Scenario. Hydrogen, bioenergy and continued use of fossil fuels for power sector and heavy industries all hinge on the successful and dramatic scaling up of CCUS. The IEA admits that CCUS deployment is “very uncertain for economic, political and technical reasons”. It calculates that failure to develop CCUS for fossil fuel would mean the transition would need to lean more heavily on wind, solar and electrolyser capacity to achieve the same level of emission reductions, requiring USD 15 trillion of additional investment.

Bioenergy: 

  • Bioenergy use increases by ~60% between 2020 and 2050. To address the concerns about land use, the IEA advocates shifting toward using “advanced bioenergy feedstocks”, including waste streams, short-rotation woody crops and feedstocks that do not require the use of arable land. Bioenergy is not a renewable source as it still drives land use change and greenhouse gas emissions, unless attached to CCUS.
  • Bioenergy use rises 3% a year on average to 100 EJ in 2050, meeting almost 20% of total energy needs. Most comes from solid biomass, followed by liquid biofuels and biogases. Solid bioenergy replaces coal in the power, industry and building sectors, reaching 60 EJ in 2050.
  • The total land area dedicated to bioenergy production increases from 330 million hectares (Mha) in 2020 to 410 Mha in 2050. In 2050, around 270 Mha is forest, representing 25% of the total area of global managed forests (or ~5% of total forest area).
  • Is it possible to deliver net-zero by 2050 without expanding land use for bioenergy? Yes, but it would require a combination of wind, solar, hydrogen and synthetic methane. However, the IEA believes this would make the energy transition significantly more expensive. The additional wind, solar, battery and electrolyser capacity, together with the electricity networks and storage needed to support this higher level of deployment, would cost more than USD 5 trillion by 2050.

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