Biogas can be a substitute for natural gas, but its application should be limited to hard-to-abate sectors where there is…
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).
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. 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 … Continue reading 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. 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 … Continue reading
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. 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 … Continue reading 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”. 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 … Continue reading 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. Chapter 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. SPM, 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. SPM, 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.” SPM, 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. SPM, 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. 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 … Continue reading 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. Chapter 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.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).
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:
Currently, the only widely practised CDR methods include afforestation, reforestation, improved forest management, agroforestry and soil carbon sequestration. SPM, 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.
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”. Chapter 12, p. 35 It is also a key element in scenarios that are likely to limit warming to 2°C or lower by 2100”. Chapter 12, p. 35 All of its IMPs use land-based CDR, which is dominated by BECCS, afforestation and reforestation. Chapter 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): Chapter 12, p. 5
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. Summary 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”. Chapter 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. Smith 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. IPCC 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”. Chapter 12, p. 56 “Stronger focus on demand-side mitigation implies less dependence on CDR and, consequently reduces pressure on land and biodiversity”. Chapter 3, p. 7 It adds that: “Within ambitious mitigation strategies…, CDR cannot serve as a substitute for deep emissions reductions”. Chapter 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. Chapter 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. Chapter 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. Chapter 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. Chapter 7, p.40 These can be split into:
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:
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.
|↑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, ↑34||Chapter 7. 42|
|↑6, ↑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.|
|↑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||Smith et al. 2019; Hasegawa et al. 2021|
|↑23||IPCC 2019, Hasegawa et al. 2021|
|↑24||Chapter 12, p. 56|
|↑25||Chapter 3, p. 7|
|↑26||Chapter 12, p. 38|
|↑27||Chapter 12, p. 39|
|↑28||Chapter 12, p. 39|
|↑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|
|↑35||Chapter 7. 116|
|↑36||Chapter 3, p. 7|
Biogas can be a substitute for natural gas, but its application should be limited to hard-to-abate sectors where there is…
A number of supplements are being tested in feedlots, but administering them on pasture, where most methane is produced, could…