Climate Change Glossary



Abated fossil fuels

Fossil fuels that have undergone interventions to significantly reduce the greenhouse gas emissions produced throughout their entire life cycle. These interventions usually involve carbon capture and storage.


Adaptation is the process of adjusting to the impacts of climate change. It encompasses a range of strategies aimed at building resilience, reducing vulnerabilities and safeguarding the well-being of human and natural systems. These strategies are context-specific so they will differ across sectors and regions. From designing resilient infrastructure to implementing sustainable agriculture practices, adaptation strategies involve a combination of physical, technological and institutional measures that are tailored to local needs.

Types of Adaptation:

The Intergovernmental Panel on Climate Change (IPCC) distinguishes various types of adaptation:

  • Anticipatory Adaptation: Adaptation that takes place before impacts of climate change are observed. Also referred to as proactive adaptation
  • Autonomous Adaptation: Adaptation that does not constitute a conscious response to climatic stimuli but is triggered by ecological changes in natural systems and by market or welfare changes in human systems. Also referred to as spontaneous adaptation
  • Planned Adaptation: Adaptation that is the result of a deliberate policy decision, based on an awareness that conditions have changed or are about to change and that action is required to return to, maintain, or achieve a desired state
  • Private Adaptation: Adaptation that is initiated and implemented by individuals, households or private companies. Private adaptation is usually in the actor’s rational self-interest
  • Public Adaptation: Adaptation that is initiated and implemented by governments at all levels. Public adaptation is usually directed at collective needs
  • Reactive Adaptation: Adaptation that takes place after impacts of climate change have been observed.


Additionality means net greenhouse gas (GHG) emissions savings or storage benefits over and above those that would have happened anyway (i.e. in the absence of a given activity or project). The term is often used in the context of carbon offsets, where a credit can offer no additionality. For example, a carbon offset project protecting an area of forest that was never under threat, or a renewable energy project that has already secured full funding, offer no additionality.

Avoided emissions

These refer to projects that do not remove carbon dioxide from the atmosphere, but merely prevent more carbon dioxide from entering it. They cannot, therefore, offset emissions. Examples include renewable energy projects.

Adaptive capacity

The ability of systems, organisations and living organisms to adapt to threats or take advantage of opportunities.


The establishment of forests on land that historically has not contained forests. As opposed to reforestation, which is replanting trees in an area that has historically contained forests.

AFOLU (Agriculture, forestry and other land use)

The term used by the IPCC to describe the wider land use sector. AFOLU groups together Agriculture and LULUCF (Land Use, Land Use Change and Forestry), which were previously treated separately.

AMOC (Atlantic Meridional Overturning Circulation)

The Atlantic Meridional Overturning Circulation (AMOC), also known as the Gulf Stream System, is a large network of Atlantic Ocean currents that is part of a global ocean circulation ‘conveyor belt’. It circulates deep, cold water across latitudes from the north to the south, and warm surface water from the south to the north. The AMOC is one of the most important modulators of global climate and weather through its impact on heat, freshwater and carbon transport.


The Anthropocene is a proposed unit of geologic time. The proposed epoch follows the Holocene – the current official geological epoch recognised by the International Commission on Stratigraphy – and brings the development of human enterprise and its transformative power up to par with the major natural geophysical forces.

Currently, the start of the epoch is the subject of much scientific debate. The point in time that garners most consensus is the detonation of the first atomic bomb (in 1945), which left a record of radioactive isotopes in both the atmosphere and the lithosphere that can still be found today.

To find out more, click here.


The term used to describe something, for example emissions or pollution, that has been caused by human activity.

AR (Assessment report)

The comprehensive reports published by the IPCC summarising the latest scientific understanding of climate change. In 2021/22, for example, the Sixth Assessment Report (AR6) was published.

Article 6

This is as key article of the Paris accord pertaining to carbon markets. It allows countries to cooperate voluntarily with each other to achieve emission reduction targets set out in their Nationally Determined Contributions (NDCs) via the transfer of carbon credits. A6 sets out two market mechanisms:

  • Article 6.2: Allows for bilateral trading of carbon credits between countries to meet NDC targets. Credits traded under A6.2 are called Internationally Transferred Mitigation Outcomes (ITMOs).
  • Article 6.4: Creates a new global carbon market overseen by a UN entity, referred to as the Supervisory Body. A project that results in emissions reduction or removal must be approved by both the country where it is implemented and the Supervisory Body before it can start issuing UN-recognised carbon credits. A6.4 is also designed to support sustainable development and mobilise the private sector to participate in climate change mitigation beyond emission reductions. This new market – sometimes called the Sustainable Development Mechanism (SDM) – will in theory replace the Clean Development Mechanism (CDM).

Article 6 also sets out one non-market mechanism – Article 6.8, which provides a formal framework for climate cooperation between countries, where no trading of emissions is involved, such as technology transfer, capacity building, development aid or taxes to discourage emissions. This is less well defined than A6.2 and A6.4.

For more information, see Article 6 and carbon markets: What is at stake?

Avoided deforestation

This occurs when forest that would have been cut down is not, for example because of a change in policy or funding. Emission reductions from avoided deforestation are almost impossible to calculate, since they are based on an imagined counterfactual scenario.


Base load/Base load capacity

Base load is the minimum amount of electric power required over a given period of time at a steady rate, i.e. the amount of power needed at all times to meet the basic demands of consumers.

Base load capacity is the generating equipment operating to serve the needs of consumers at all times.

BECCS (Bio-energy with carbon capture and storage)

The process refers to the production of energy using organic materials (biomass), where the carbon dioxide emitted from this process is then captured and stored, ideally permanently.

It is controversial given the amount of land needed for biomass production – land which could be put to better use, for example growing food – and questions over carbon capture and storage (CCS).

BEV (Battery electric vehicle)

Battery electric vehicles are those that are powered exclusively by an electric motor, powered by a battery.

It can also be described as:

  • Pure electric vehicle
  • Only-electric vehicle
  • Fully electric vehicle or
  • All-electric vehicle.

Bi-fuel vehicle

A motor vehicle that operates on two different fuels, but not on a mixture of the fuels. Each fuel is stored in a separate tank.

Biodiversity credits

Biodiversity credits, or biocredits, are investments, typically voluntary, in projects that support biodiversity conservation, but which do not imply biodiversity loss elsewhere. For more information click here.

Biodiversity offsets

Biodiversity offsets are a form of impact mitigation, often mandatory, that aim to compensate for biodiversity loss from developments such as mines by protecting or restoring similar habitat elsewhere. For more information click here.


Biogas is produced from the controlled decomposition of organic matter (through processes like anaerobic decomposition), where the gases that form as a result are captured. These gases are usually a mixture of methane and CO2, which are both potent greenhouse gases. Additional processes can be applied to remove the CO2 from biogas, leaving only methane, which is known as biomethane.


In the context of climate change, biomass refers to plant-based (organic) matter used as a fuel to produce heat or electricity.

Blue Carbon

This is carbon stored in coastal and marine ecosystems, such as algae, seagrasses, seaweeds, mangroves and salt marshes. Such ecosystems sequester and store large amounts of carbon, both in plants and in the sediments below.

For example, the ocean has sucked up about a quarter of the CO2 released since we began burning fossil fuels for energy during the Industrial Revolution. Phytoplankton are the main reason – these microscopic marine algae and bacteria absorb about as much carbon as all the plants and trees on land combined. [Source]


Cap and trade

Cap and trade, or emissions trading, is a system designed to reduce greenhouse gas emissions.

Companies are allowed to emit a certain amount of carbon dioxide and no more (the cap). If a company wants to emit more, it has to buy permits, issued by the government, representing units of emissions. Companies are free to buy and sell these permits (the trade). The idea behind the system is to put a price on emissions, thereby encouraging companies to reduce them. However, the price of these permits has always been too low (partly through over-issuance), so companies can simply buy them to avoid making meaningful emissions reductions. For the system to work effectively, the price of the permits (often referred to as the carbon price) needs to rise.

Capacity factor

This is a measure of a how close to its maximum capacity a power plant is running over a period of time. It is calculated by dividing the plant’s actual output by the amount of power it would have produced had it been running at 100% of its capacity over that time. So, in theory, a 1MW power plant would have a 100% capacity factor over a year if it produced 1 MWh of electricity for every hour in that year (8760 MWh in total). However, in practice, no power plant runs at 100% of its capacity, though some have higher capacity factors than over. Renewables have a lower capacity factor (around 30%-40%) than conventional fossil fuel plants (around 60%).

Carbon budget

A carbon budget is the cumulative amount of CO2 emissions permitted over a period of time to keep within a certain temperature threshold.

The remaining carbon budget for 1.5C goals is 272 gigatonnes, which at current rates of emissions will be used up in 6 years, 5 months (as at 9 February 2022). [Source]

Carbon farming

Farming practices that are known to improve the rate at which CO2 is removed from the atmosphere and converted to plant material and/or soil organic matter.

For more information, click here.

Carbon lock-in

Carbon lock-in happens when high-emission infrastructure, such as coal power plants, continue to be used, despite low-emission alternatives being available. This delays or prevents the transition towards near-zero or zero-emission technologies.

Carbon markets

Carbon markets are where carbon offsets (see below), also known as carbon credits, are traded. They exist under both mandatory (compliance) schemes and voluntary programmes.

Compliance markets are regulated markets. They are used by companies and governments to obtain and surrender emissions permits (allowances) or offsets in order to meet predetermined targets. They are regulated by regional, national or international carbon reduction regimes.

Voluntary markets (see below) are unregulated. They function outside compliance markets and enable companies and individuals to trade carbon credits on a voluntary basis.

Carbon offsets

Otherwise known as carbon credits, these are created by projects that remove carbon from the atmosphere, such as afforestation or DACS (see below). Companies can buy these credits to offset their emissions – in theory, if a company emits 10 tonnes of carbon dioxide and buys 10 tonnes worth of carbon credits, it is carbon neutral.

However, many projects issuing credits today do not remove carbon dioxide from the atmosphere, for example renewable energy and forest protection. In fact only 5% to 10% of granted offsets in the voluntary market actually remove carbon from the atmosphere. The rest merely ‘avoid’ further emissions. 

It’s important to note that even if you could remove as much CO2 as is being emitted, the full suite of damage caused by GHGs cannot be fully countered. The 2021 IPCC AR6 WGI report highlights that some changes, such as sea-level rise and arctic sea ice melt, only reverse after several millennia, even if CO2 concentrations in the atmosphere fall.

For more information, see Carbon offsets and net-zero or Emission cuts are better now than later.

Carbon price

This is the price of carbon, as traded in various carbon trading schemes around the world. Each scheme has a different price.

Carbon tax

A carbon tax is a government-imposed levy targeting individuals or businesses based on the carbon they emit by burning fossil fuels. The tax sets a direct price on carbon by levying charges on greenhouse gas emissions or on the carbon within fossil fuels. Its main objective is to reduce emissions and to encourage reductions in the use of fossil fuels.

Carbon sequestration

Carbon sequestration refers to the process of capturing and storing carbon in carbon pools, which is a location where carbon is stored such as forests or the ocean. This can occur via natural processes or as a result of human activities. 

According to the IPCC, carbon dioxide removal differs from carbon sequestration in that it refers only to human activities that remove CO2 from the atmosphere and “excludes natural CO2 uptake not directly caused by human activities.”

For more information, click here.

Carbon sink

A carbon sink is anything that absorbs more carbon from the atmosphere than it releases – for example, plants, the ocean and soil.

Carbon leakage

A term used to refer to the problem where a given industry or company relocates production to countries where regimes and legislation regarding emissions are weaker.

CBAM (Carbon border adjustment mechanism)

The CBAM is a proposed carbon tariff on carbon-intensive products, such as cement and some electricity, imported by the EU.

It is expected to come into force in 2023 in a transitional form, before being fully applied from 2026.

CCS (Carbon capture and storage)

This is the process of capturing and storing CO2 before it is released into the atmosphere.

Once the CO2 has been captured, it is compressed into liquid state and transported by pipeline, ship or road tanker. It can then be pumped underground, usually at depths of 1km or more, to be stored into depleted oil and gas reservoirs, coal beds or deep saline aquifers, where the geology is suitable

Despite high hopes, CCS has proved difficult to scale up, largely due to cost.

For more information, click here.

CCUS (Carbon capture utilisation and storage)

Like CCS, but where the CO2 is pumped into oil wells to extract as much oil as possible, a process known as enhanced oil recovery. This means that CCUS is, at best, carbon neutral, but often leads to increased emissions.

CDR (Carbon dioxide removal)

CDR is the broad umbrella term given to a set of technologies that aim to remove carbon dioxide permanently from the atmosphere.

The most established technologies, though not yet proven at scale, are bioenergy with carbon capture and storage (BECCS) and direct air carbon capture and storage (DACS).

Processes that capture CO2 and turn it into durable products, such as cement or building insulation, count as they reduce CO2 levels over the long run. Processes that capture CO2 in short-lived products, such as beverages or plastics, do not, because they only store carbon temporarily.

CO2 equivalent (CO2e or CO2-eq)

A CO₂ equivalent (CO₂e) is a unit of measurement used to standardise and therefore compare the climate effects of various greenhouse gases.

Specifically, it is used to convert the amount of other gases to the equivalent amount of carbon dioxide with the same global warming potential.

COM (Compliance offset market)

See carbon markets above.


COP stands for Conference of the Parties and is the name given to the United Nations Climate Change Conferences. The goal of these conferences is to review progress made by members of the United Nations Framework Convention on Climate Change (UNFCCC) to limit climate change.

It is the main decision-making body of the UNFCCC, including representatives of all the countries that are signatories

The last conference, COP27, was held in Sharm el-Sheikh, Egypt in November 2022.

For more information, click here.

Climate Action 100+ Initiative

This is an initiative designed to ensure that the world’s largest greenhouse gas emitting companies take action on climate change. It explicitly targets 167 companies that constitute 80% of global industrial greenhouse gas emissions (as at January 2022).

For more information, click here.

Climate justice

Climate justice recognises the unequal impact of climate change on the Global South and low-income countries. It identifies climate change as a result of unjust economic, social and political systems, primarily in the Global North. Advocates of climate justice work to address these systemic issues and rectify the disproportionate effects of climate change.

Climate models

These are computer simulations that factor in a large number of variables, such as air pressure, rainfall, greenhouse gases and wind, to predict future changes in the climate. Scientists use these models to estimate the impact of human actions, such as increasing levels of greenhouse gases in the atmosphere, on temperature and sea-level rise.

For more information, click here.

Climate sensitivity

Climate sensitivity is a measure used by the IPCC to describe the impact on the Earth’s temperature of a change in the climate system, for example a rise in greenhouse gases.

Common but differentiated responsibilities (CBDR)

Common but differentiated responsibilities (CBDR) is a principle of international environmental law asserting that all states are responsible for tackling environmental destruction, but not equally responsible. The principle, established in 1992 and frequently referred to in international negotiations, recognises the wide differences in levels of economic development between states.

Country pledges

These are pledges made by countries at the COP. They set a date for achieving net zero or other commitments, such as halting deforestation or using coal for power generation. Examples include:

  • EU: Net-Zero GHG by 2050
  • USA: Net-Zero GHG by 2050
  • China: Net-Zero CO2 by 2060 (but peak before 2030)
  • Japan: Net-Zero GHG by 2050 (but low transparency)

For more information, click here.

Cumulative emissions

The cumulative sum of a country’s or company’s historical emissions is one indicator that tries to capture the contribution they have made to climate change.

CSP (Concentrated solar power)

Concentrated solar power (as opposed to photovoltaic solar power) is an approach to generating electricity in which mirrors are used to reflect, concentrate and focus sunlight onto a specific point. The concentrated light is converted into heat, which in turn is used to create steam. The steam is then used to drive a turbine that generates electricity.


DACS/DACCS (Direct air capture with carbon storage)

This is a technology that uses chemical processes to capture CO2 directly from the air and store it in geological reservoirs or use it to make long-lasting products, such as cement.

As with all CDR technologies, there are some downsides, namely it requires significant amounts of energy, which must be low-carbon to maximize the technology’s climate impact. Diverting low-carbon energy to DACS means it cannot be used to displace fossil fuel power generation. Transporting and injecting CO2 into geological reservoirs also raises concerns about pipelines and CO2 leakage.

DACS is currently too expensive to deploy at the scale required, but costs will fall.

For more information, click here.

Deep sea mining

The process of extracting mineral deposits from the deep seabed, typically at depths ranging from 200 to 6,500 metres. This practice is highly controversial due to its potential to damage habitats and drive species towards extinction.


A term used in the oil and gas industry to describe processes associated with with the distribution and sale of products (as opposed to upstream, which is processes associated with production, such as exploration and drilling).

Drop-in fuel

A drop-in fuel is a synthetic alternative that is completely interchangeable with conventional hydrocarbon fuels (gasoline, jet fuel and diesel). See also e-fuels and synthetic fuels.


ECT (Energy Charter Treaty)

The Energy Charter Treaty is a multilateral agreement that came into force in 1998 establishing a framework for trade and investment in the energy sector.

It was initially developed to secure energy supply for Western Europe in the context of the post-Cold War transition. Its most important provisions focus on the trade in energy materials and products, and the resolution of investment disputes.

There are currently 53 contracting parties to the ECT (as at February 2023).

The ECT has become increasingly controversial as it is used to protect investments in fossil fuels. It can be used by private companies to prevent public authorities from regulating and developing public policies needed for a just transition. Under the treaty, authorities have to compensate private companies for any lost profits resulting from clean energy legislation.

For more information, click here.


Electrofuels, also known as e-fuels or synthetic fuels, are a type of drop-in replacement fuel. They are manufactured using captured carbon dioxide or carbon monoxide, together with hydrogen obtained from sustainable electricity sources such as wind, solar and nuclear power.

For more information, click here.

El Niño

El Niño is a natural climate pattern whereby the sea surface in the tropical Pacific becomes warmer than usual. Normally, trade winds – the east-to-west winds that blow along the earth’s equator – move warm water from South America to Asia. The warm water is then replaced by cooler water from deeper levels, known as upwelling, which brings nutrients to the surface and creates fertile conditions for fishing. During El Niño, trade winds weaken, causing warm water to gather in the Pacific Ocean. El Niño occurs every two to seven years and usually lasts nine to 12 months, but can last years.

For more information, click here.

Emissions scope 1, 2 and 3

These refer to the greenhouse gases that individuals, companies or countries pump into the atmosphere. Depending on how they are defined, they usually refer to all GHGs or to CO2. When it comes to corporate emissions, there are three types (for more detail, see ‘Scope 1, 2 and 3 emissions’ below):

Scope 1: Most direct emissions (company-owned and controlled resources)Scope 2: Emissions beyond the company’s immediate controlScope 3: Indirect and supply chain emissions
Examples include company facilities, fuel combustion, company vehicles, fugitive emissionsExamples are purchased electricity and heat productsThey include purchased goods and services, business travel, employee commuting, use of sold products, transportation and distribution, investments, leased assets and franchises

Energy poverty (fuel poverty)

Energy poverty refers to households where energy bills form a high proportion of income and, as a result, the people in that household are unable to afford adequate heating (or lighting). Different countries have different definitions of how to quantify levels of energy poverty.

Enhanced weathering

This is a carbon capture technology that involves spreading large amounts of finely ground rock on to the land or sea/ocean surface. This increases surface alkalinity, thereby increasing CO2 absorption. The process aims to speed up the natural weathering processes of silicate and carbonate rocks, a slow carbonation process that is estimated to consume and absorb about one billion tonnes of CO2 from the atmosphere every year. [Source]

EOR (Enhanced oil recovery)

Also called tertiary recovery, EOR is used to increase the flow of oil from a well by injecting water, chemicals or gases into the reservoir, or by changing the physical properties of the oil.

The term is often used when talking about carbon capture and storage, where carbon dioxide is captured and pumped into an oil well to extract as much oil as possible.

For more information, click here.

ETS (Emissions Trading System)

This is the name given to carbon markets.

For more information, click here.


Fossil Fuels

This is the collective term for coal, oil and natural gas, all fuels that were formed long ago from decomposing plants and animals. Together they are the main driving force behind rising GHG emissions and, therefore, climate change. Taking into account primary production and all uses, they account for about 75% of emissions.

To find out more, click here.

Fischer-Tropsch process

The Fischer-Tropsch process involves a set of chemical reactions that convert a mixture of carbon monoxide and hydrogen into transportation fuels or liquid hydrocarbons.

For more information, click here.


Fracking is the process of pumping water and chemicals at high pressure to crack shale rock formations deep underground in order to release trapped natural gas. The practice has been widely adopted in the US, but it remains controversial due to fears over water use and contamination, and earth tremors, and so has been banned in a number of countries including France, Germany and Spain.



Gas/natural gas

Natural gas is one of the three main fossil fuels (see above). In its final form, after impurities have been removed, it is composed almost entirely (around 90%) of methane

The oil & gas industry often argues that natural gas is a clean fuel, but this is only in comparison with coal – gas actually emits about half as much CO2 when burned as coal. Leaking methane – a much more potent GHG than natural gas – during transportation and storage is also a big contributor to climate change. Indeed recent studies suggest that, when taking leaking methane and transport into account, gas has a similar impact on the climate as coal.

For more information on the role of gas in a Paris-aligned world, click here.

GGR (Greenhouse gas removal)

Similar to CDR, this is the removal of greenhouse gases from the atmosphere by deliberate human activities.

For more information, click here.

GHG (Greenhouse gases)

This is the collective term for all the main gases that contribute to global warming.

The major anthropogenic greenhouse gases are:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • Three groups of fluorinated gases – sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs)

Less recognised and discussed than CO2 are the increasing emissions of methane and nitrous oxide, which trap about 30 and almost 300 times more heat than CO2 respectively (over a 100 year period).

Currently, both methane and nitrous oxide emissions are well above the safe limits outlined by the IPCC, due to emissions from the fossil fuel and agriculture sectors.

For more information, click here.


A gigatonne is a billion metric tonnes. It is often used when discussing emissions on a national or global scale.

Here is a GHG equivalence calculator.


A gigawatt is one billion watts.

GWP (Global Warming Potential)

Global Warming Potential is a metric to compare the ability of each greenhouse gas to trap heat in the atmosphere. Carbon dioxide was chosen as the reference gas to be consistent with the guidelines of the IPCC.

The larger the GWP, the more a given gas warms the Earth compared to CO2 over that time period.

For more information, click here.

Global Stocktake

The Global Stocktake is a key element of the Paris Agreement that assesses countries’ progress towards their climate mitigation and adaptation objectives. This process is carried out every five years. The first report, published in October 2023, revealed that the world is not on track to meet the Paris Agreement goal of limiting warming to 1.5 degrees celsius.

For more information, click here.

Greenhouse effect

The greenhouse effect describes the process by which heat from the sun is trapped in the Earth’s atmosphere, thus heating the planet. It is greenhouse gases that prevent some of this heat reflecting back into space.


This is the word used to describe companies paying lip service to sustainability and environmental policies but, in reality, taking very little action to reduce their impact on the environment. It often comes in the form of deliberately misleading claims, such as airlines claiming flights are carbon neutral when the offsets they rely on are not verified, or banks highlighting investment in renewable energy when they also invest heavily in fossil fuels.


Hard-to-abate sectors

This term refers to those sectors where emissions reductions are hardest, either because they lack the technology or the cost remains prohibitive.

Examples of hard-to-abate sectors are cement, iron and steel, and chemicals.

Heat pumps

A heat pump is an electrical device that extracts heat from a low temperature source and then delivers it to a higher temperature place (i.e. against the natural flow of heat). The source of heat can be the ground, the air or water.

The technology underpinning heat pumps has been around for decades, but they are enjoying a surge in popularity as they offer a low-carbon alternative (when powered by renewable energy) to natural gas for heating buildings.

For more information, click here.

Historical emissions

Historical emissions refer to the amount of carbon dioxide emitted by a specific country or company since the beginning of the industrial revolution.

The top emitters, as of 2021, are:

    • US: 20%

    • China: 11%

    • Russia: 7%

    • Brazil: 5%

    • Indonesia: 4%

    • Germany: 4%

    • India: 3.5%

    • UK: 3%

Today, 15 economies make up 72% of global emissions.

For more information, click here.


This is the term given to a vehicle that runs on both an internal combustion engine (ICE) and an electric motor. Because of the electric motor, they are more efficient and can, therefore, drive further on the same amount of fuel than ICE vehicles. The battery on a hybrid is charged by the ICE and by regenerative braking. Also see ‘Plug in hybrid’.


Hydrogen is a gas that is increasingly being talked about as a cleaner alternative to natural gas.

It is the most abundant element in the universe, but almost never exists in a pure form on earth. Instead, it is found combined with oxygen in the form of water.

Hydrogen gas can be extracted from water by a technique known as electrolysis, which involves running a high electric current through water to separate hydrogen and oxygen atoms. The electrolysis process is pretty expensive since it requires a lot of energy. An alternative process to split hydrogen is called steam methane reforming (SMR), which involves the use of fossil fuels. The output is called “grey hydrogen” as it emits CO2.

Hydrogen can be used in a fuel cell to produce electricity. The byproducts generated in the fuel cell are water and heat.

Types of hydrogen:

    • Grey: Uses fossil fuels and releases carbon dioxide (SMR – steam methane reforming)

    • Blue: Uses natural gas, but the carbon dioxide is captured and stored

    • Green: Electrolysis is used to split water into hydrogen and oxygen using renewable energy

    • Pink hydrogen: Is generated through electrolysis powered by nuclear energy. Nuclear-produced hydrogen can also be referred to as purple or red hydrogen.


    • Turquoise hydrogen: Hydrogen made using a process called methane pyrolysis to produce hydrogen and solid carbon. This process has not yet been proven at scale. [Source]

Here is a nice video if you want to know more.



IAM (Integrated assessment models)

IAMs refers to a broad category of research approaches in climate change science. They are designed to help us understand how the choices we make affect the natural world, including climate change, by modelling the numerous interactions between human and natural systems.

There are two basic types of IAM. So-called simple IAMs compare the costs and benefits of avoiding different levels of warming. Examples include “DICE”, “FUND” and “PAGE”, which can be used to measure the impact of emitting a certain amount of CO2, in monetary terms. More complex IAMs look at a wider range of inputs, such as new energy technologies and land-use change, that contribute to, or mitigate, greenhouse gas emissions.

ICE (Internal combustion engine)

This refers to the mechanical engine that drives traditional cars, vans and trucks. ICE vehicles run on petrol or diesel.


Insetting is a term coined by companies claiming to internalise the carbon reduction process. Instead of buying carbon credits from unrelated third parties, as with carbon offsetting, companies claim to invest in projects that reduce or remove carbon within their supply chains. 

Much like offsetting, insetting is highly controversial due to the challenge of measuring its effectiveness and its indirect approach to emissions reduction.

For further info: Corporate Climate Responsibility Monitor 2023

Intensity of emissions

This refers to the amount of emissions per unit of output. For example, some fossil fuel companies set climate targets for intensity of emissions, rather than absolute (overall) emissions.

This means it can maintain or even increase fossil fuel production while adding a small proportion of clean energy on top, which reduces the intensity but not the overall emissions caused by its products. 

For more information, click here.


The IPCC is the scientific advisory body for the UN on climate change. Formed under the United Nations Environment Programme (UNEP), thousands of scientists and experts contribute to the IPCC on a voluntary basis to help understand climate change.

Every six to seven years, the IPCC publishes a review of the latest science on climate change, which is seen as the most authoritative synthesis of our understanding of the subject.



JETP (Just Energy Transition Partnership)

Just Energy Transition Partnerships are a financing model designed to ensure effective financing for a just transition in global south countries. The South African JETP was announced at COP26 and saw France, Germany, the UK, US, and EU commit to providing USD 8.5 billion over three to five years to support South Africa’s national climate plan. Pilot projects to develop JETPs for Egypt, Ivory Coast, Kenya and Morocco were also announced in February 2022.

Questions have been raised about the transparency of JTEPs, and the use of funds to expand natural gas production.

Just transition

Just Transition is a set of principles designed to ensure that the energy transition and move to a low carbon economy is fair and inclusive , ensuring that equal opportunities are afforded to everyone so that no group is left behind.


The Just Transition Mechanism is a European Commission project that aims to ensure the transition to a fair economy by mobilising funds towards impoverished and disadvantaged areas.

For more information, click here.




A watt is a measurement of electrical power. A kilowatts (KW) = 1,000 W.



Land Use

Agriculture, forestry and other land use (AFOLU) account for about 25% of global emissions. Securing a way to low-carbon food production is not only important for mitigating climate change, but is also central for food security and sustainable development worldwide.

    • Low-meat, vegetarian and vegan diets could significantly cut land use emissions

    • Changes to food and biomass production can cut emissions

    • Afforestation, sustainable forest management and reducing deforestation can have a big impact in some regions.

La Niña

La Niña acts in the opposite way to El Niño. During La Niña events, trade winds are even stronger than usual, pushing more warm water to Asia. Off the west coast of the Americas, upwelling increases, which brings cold, nutrient-rich water to the surface.

During La Niña, winter temperatures are warmer than average in the south and colder than average in the north. La Niña typically lasts between one and three years and occurs every three to five years.

For more information, click here.

LCOE (Levelised cost of energy)

This is the cost of electricity generation over the lifetime of a power plant. It is based on a calculation of the current value of the costs of building and operating a power plant over its lifetime. It allows a comparison of the costs of different technologies even if they have different fuel costs, life spans, capacities and financial profiles. 

LNG (Liquified natural gas)

Gas can be turned into liquid form – by reducing its temperature dramatically to condense it – for ease of transportation, especially across water. The liquid form of gas is called LNG.

Loss and Damage

Loss and damage refers to those inevitable impacts of climate change experienced by the Global South that have not been avoided through mitigation and adaptation due to socio-political or economic constraints, or that cannot be avoided because it is impossible to do so. It may encompass a wide range of circumstances, including:

    • Extreme weather or rapid-onset events, such as storms, cyclones, heatwaves and floods

    • Slow-onset events, such as drought, desertification, increasing temperature, land degradation and sea level rise 

    • Non-economic impacts, such as the loss of cultural heritage, animals, plants and tradition 

    • Economic impacts, such as loss of lives, livelihoods, homes, agriculture and territory.  

For more information, click here.

LPG (Liquified petroleum gas)

This is a hydrocarbon gas that exists in a liquefied form. LPG is a colourless, low carbon and highly efficient fuel. LPG is composed of either Butane or Propane.


LUC (Land-use change)

Land-use change refers to the conversion of land by humans from one purpose to another, for example through agriculture, afforestation, deforestation or housing.



MACC (Marginal abatement cost curve)

MACCs present the expected costs or savings from different initiatives and compares them with the potential emissions reductions that could be achieved. They use the metric of dollars per tonne of carbon dioxide equivalent – usually represented as $/tCO2e.

MDBs (Multilateral development banks)

Multilateral development banks (MDBs) are supranational institutions created by sovereign states, which are their shareholders. The main objective of the MDBs is to support economic development and reduce poverty in member countries by financing projects and programmes that promote sustainable growth, infrastructure development and social welfare. Examples include the World Bank and the International Monetary Fund.


Methane is a key greenhouse gas (see ‘Greenhouse gases’ above). Mitigating Methane can have a more immediate impact on temperatures due to the gas’s shorter lifetime in the atmosphere.

Methane causes over 30 times more warming than CO2 (over a 100 year period). Scientists have shown that, even if CO2 emissions are Paris-aligned, ignoring methane emissions will lead to overshooting the Paris-agreed temperature goals.

Natural gas is a hydrocarbon fuel composed almost entirely of methane. The oil and gas industry have run a successful PR campaign establishing gas as a “clean/transition” fuel that emits less CO2 than coal. But this does not account for the fugitive emissions of methane that are released both intentionally and unintentionally during the production and transportation of oil and gas. Indeed recent studies suggest that, when taking leaking methane and transport into account, gas has a similar impact on the climate as coal.

The IEA estimates that the oil and gas industry can cut down 40%-50% of methane emissions very cheaply.

Methane also contributes to the formation of ground-level ozone, which has adverse health impacts for humans and affects agriculture.

The main sources of methane are:

    • 52%: Coal mining

    • 13%: Enteric fermentation and manure (cattle)

    • 17%: Oil and gas

    • 15%: Landfills and waste

For more information, see this Methane emissions Q&A.

MEPS (Minimum Energy Performance Standards)

These contain certain performance requirements for a given energy-using device. MEPS limit the amount of energy that may be consumed by a product when conducting a certain task.

For more information, click here.


Mitigation refers to efforts aimed at reducing or preventing the emission of greenhouse gases (GHGs) into the atmosphere to limit global warming and its associated impacts on the planet. Mitigation efforts can take several forms, but must engage the private sector, and local and national governments.

A primary mitigation strategy is to promote the use of renewable energy sources to reduce human society’s dependence on fossil fuels, the main cause of climate change. Other measures include improving energy efficiency in buildings, industry, and transportation; promoting sustainable agriculture; and adopting sustainable forestry practices.

Mitigation vs Adaptation

Climate change mitigation and adaptation are two concepts that are often confused with each other. While they both address the issue of climate change, they are distinct approaches with different goals:

Here are the main differences between climate change mitigation and adaptation:

Climate Change Mitigation:

    • Focuses on reducing greenhouse gas emissions to prevent or limit the extent of global warming and its impacts

    • Involves shifting to cleaner energy sources and improving energy efficiency

    • Seeks to address the root cause of climate change

Climate Change Adaptation:

    • Focuses on reducing vulnerability to the impacts of climate change that are already occurring or expected to occur

    • Involves implementing strategies to adapt to changing climate conditions and reduce the risks associated with them

    • Seeks to address the consequences of climate change and build resilience.

See more here.

Mtoe (Million tonnes of oil equivalent)

This is used to describe the energy content of any fuel by benchmarking it against the energy released by burning one tonne of crude oil. 

MW (Megawatt)

A watt is a measurement of electrical power. A megawatt is 1,000,000 watts and is commonly used to describe the generating capacity of power plants. Kilowatts (KW) and Gigawatts (GW) are also widely used. KW = 1,000 W and 1 GW = 1,000,000,000 W.


MWh (Megawatt hour)

This is a measurement of electrical output or demand equal to 1MW for 1 hour. It is used for showing how much electricity is produced or used over a certain period of time.



NAPs (National Adaptation Plans)

National Adaptation Plans are frameworks that countries develop to reduce their vulnerability to the impacts of climate change. NAPs involve assessing the potential impacts of climate change on various sectors and identifying measures to reduce risks and build resilience of communities and sectors. The development of NAPs is guided by the UN Framework Convention on Climate Change (UNFCCC).

Natural Gas

See ‘Gas’ above.

NBS (Nature-based solutions)

NBS are defined by International Union for Conservation of Nature (IUCN) as “actions to protect, sustainably manage and restore natural or modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits”.

The science indicates that there’s a real but limited benefit nature can have on mitigating climate change without dramatically changing the Earth’s existing ecosystems.

It’s estimated that, in total, nature has the cost-effective potential to remove about 11.3 billion tonnes of CO2 from the atmosphere each year by 2030, equivalent to roughly a third of current annual carbon emissions from energy use.

One of the biggest immediate benefits of nature to climate action is its contribution towardsadaptation. Ecosystems rich in biodiversity tend to be more robust, offering better protection against the effects of the changing climate.

NCQG (New collective quantified goal on climate finance)

The new collective quantified goal on climate finance (NCQG) is a global climate objective initiated under the Paris Agreement. It aims to set a new goal for global spending on climate finance, from a floor of USD 100 billion per year, before 2025. The goal will be set in the context of substantial mitigation efforts and will consider the specific needs and priorities of developing nations.

For more information, click here.

NDCs (Nationally determined contributions)

These are the carbon reduction targets that countries submit at COP, starting in 2020 (the official start date of the Paris Agreement).

These targets outline a country’s commitment through to 2025 or 2030. Countries are expected to revisit these and set new, more ambitious targets every five years.

For more information, click here.

NET (Negative emissions technology)

These are technologies designed to reduce the absolute amount of CO2 in the atmosphere.

Examples include:

a) Biological carbon dioxide removal:

    • adapted land management

    • pyrolysis (heating in the absence of oxygen) of biomass to form charcoal that keeps carbon in the soil for many years

    • afforestation

    • reforestation

b) Technological carbon dioxide removal:

    • like direct air capture with carbon capture storage (DACS)

    • bio-energy with carbon capture and storage (BECCS)

For more information, click here.

Net Zero

This is the concept of reducing emissions by as much as possible, then offsetting whatever is left. In other words, any GHGs that are still being emitted are balanced out by removing the same amount of GHGs from the atmosphere. Once net zero is achieved, the overall stock of GHGs in the atmosphere does not increase. For a basic introduction to net zero, click here.

The IPCC states that we must cut emissions to net zero by 2050 for a 50% chance of limiting warming to 1.5°C. In order to achieve this, we have to cut emissions by 45% from 2010 levels by 2030. This requires transformational and rapid decarbonisation of the energy, food, transport and industrial sectors.

It’s important to note that even if it were possible to remove as much carbon dioxide as is being emitted, the full range of damage caused by GHGs cannot be fully countered. The 2021 IPCC AR6 WGI report highlights that some changes, such as sea-level rise and arctic sea ice melt, only reverse after several millennia, even if emissions are removed from the atmosphere and oceans.


NZE (Net Zero Emissions by 2050 Scenario)

The NZE is an attempt by the International Energy Agency (IEA) to map out how we might get to net zero.



Ocean CDR (Ocean carbon dioxide removal)

The same principal as CDR, but ocean based. There are various ways of increasing the storage of carbon dioxide in the ocean, such as adding nutrients or increasing the rate of mixing of deep water with surface water to help marine plants absorb more CO2.



For more information, click here.


See ‘Carbon offsets’



Paris Agreement

The landmark international climate change agreement signed in Paris in 2015. The treaty aims to limit global warming to well below 2°C and preferably to 1.5°C, compared to pre-industrial levels.

It also calls for a five-year cycle of increasingly ambitious climate action carried out by individual countries, known as NDCs (see above).

For more information, click here.


The gradual reduction of fossil fuel usage over successive periods until there is no further use. A phase-out aims to achieve net-zero emissions from fossil fuels by 2050 by completely stopping their use.


The gradual reduction in the use of fossil fuels over successive periods, but not to the point of complete elimination. Fossil fuels would be reduced to a level considered acceptable to continue indefinitely. A phase-down requires the development and expansion of carbon capture and storage technology to offset emissions.

PHEV (Plug in hybrid electric vehicle)

This is a vehicle that is powered by both an internal combustion engine (ICE) and an electric motor. The battery in a PHEV is charged by connecting to a power supply, unlike a standard hybrid, where the battery is charged by the ICE and regenerative braking. The advantage of a PHEV is that it can be driven purely in electric mode for much longer distances.

Photovoltaic solar power (Solar PV)

This the process of converting sunlight into electrical energy. More specifically, solar panels consisting of layers of cells made from semi-conducting materials – usually silicon – create a flow of electricity when light shines upon them. Direct sunlight is not required – indeed solar panels can work on cloudy days – but the stronger the sunlight, the more electricity is created.

See also ‘Concentrated solar power (CSP)’.


Companies looking to reduce their environmental footprint make pledges to cut their emissions by a certain amount by a set date. Pledges must be scrutinised carefully, as the headline often belies the detail. For example, what emissions (scope/absolute vs intensity) and GHGs are covered, and does the pledge rely heavily on offsets? Pledges should be immediate, verifiable and adequate.

Things to watch out for:

    • Does this climate plan say what proportion of emissions reductions are being attributed to offsets, and does it clearly separate CO2 removal targets from emissions-reductions goals?  

    • Are the offsets removing CO2 or just avoiding more emissions? If it’s the latter, they should not count as offsets, as they are not actually offsetting current emissions.

    • If they are temporary, are they permanent? If they are relying on nature-based solutions, how will the offsets be monitored into the future?

    • What justification has the company presented for using offsets?

For more information, see Net zero assessments and Net zero map



This refers to the conversion of renewable energy into liquid and chemical fuels, such as methanol, oxymethylene ether and ammonia. These energy-dense fuels are needed for aircraft and ships that are too heavy or travel too far to rely on batteries and electricity.



Renewable energy

Renewable energy is energy produced from sources such as the sun and wind that are naturally replenished and theoretically won’t run out on a human timescale. Renewable energy can be used for electricity generation, space and water heating and cooling, and transportation. For most renewable energies, there are no fuel costs, so lifetime costs are much lower than for fossil fuels. Indeed in most global markets, renewable energy is already cheaper than fossil fuels.

Types of Renewable Energy include:

    • Solar Energy

    • Wind Energy

    • Bioenergy

    • Geothermal Energy

    • Hydropower

    • Marine Energy

Source: Elements.VisualCapitalist


An energy storage system connected to a solar or wind plant. Since these projects pair more than one technology (for example, solar electricity panels and batteries), they are also known as hybrid renewables projects.

For more information, click here.

R2Z (Race to Zero)

This is a UNFCCC coalition of net-zero initiatives, representing 1,136 cities, 52 regions, 8,307 companies, 595 financial institutions and 1,125 education institutions (as at March 2023).

The goal is to achieve net-zero carbon emissions by 2050 at the latest.

For more information, click here.



REDD+ is backed by the UN and aims to help in the fight against climate change by creating incentives for developing countries to stop deforestation, thereby

REDD stands for Reducing Emissions from Deforestation and forest Degradation, while the + signifies the role of conservation and sustainable management of forests.



SBTi (Science-based Target Initiative)

This is a partnership between CDP (formerly the Carbon Disclosure Project), the UN Global Compact, World Resources Institute (WRI) and the World Wide Fund for Nature (WWF) that sets standards for net-zero targets.

1.5°C-aligned pathways used by the SBTi stay within a 500 gigatonnes (GT) carbon budget under the assumption of about 20GT-40 GT of cumulative CO2 removal by 2050.

For more information, click here.

Scope 1 emissions

Emissions from sources that the company owns and controls directly, including company facilities, fuel combustion, company vehicles and fugitive emissions.

Scope 2 emissions

Emissions from services that the company has purchased. For example those that come from the facility where the electricity the company uses is generated, including electricity, heating/cooling and steam products.

Scope 3 emissions

Scope 3 is an optional reporting category that allows for the treatment of all other indirect emissions – in other words, emissions from the entire value chain. They therefore occur from sources not directly owned or controlled by the company.

They include purchased goods and services, business travel, employee commuting, waste disposal, use of sold products, transportation and distribution, investments, leased assets and franchises. In the case of fossil fuel companies, they also include the consumption (or burning) of fossil fuel products.

Scope 4 emissions

Scope 4 emissions are not an established category yet. It’s an additional scope that companies can report to show how they are enabling others to reduce emissions.

For example, if a manufacturing company produces a more energy-efficient bread oven, the bakeries that bought those ovens could, all else being equal, reduce their emissions. However, the bread oven manufacturers will see their carbon footprint increase with every bread oven they sell. Another example is emission reductions through employees working from home.

SDGs (Sustainable Development Goals)

The Sustainable Development Goals are a set of 17 global objectives established by the UN General Assembly in 2015 as part of the 2030 Agenda for Sustainable Development. The SDGs are designed to be a universal call to action to end poverty, protect the planet and ensure that all people enjoy peace and prosperity by 2030.

Each goal is accompanied by specific targets and indicators. Achieving them requires collaboration and partnerships between governments, the private sector and civil society.

These are the 17 SDGs:

Shale gas

Also known as fracking, this is the process of pumping water and chemicals at high pressure to crack shale rock formations deep underground in order to release trapped natural gas. The practice has been widely adopted in the US, but it remains controversial due to fears over water use and contamination, and earth tremors, and so has been banned in a number of countries including France, Germany and Spain.

SRM (Solar radiation management)

Also known as solar geoengineering, SRM is a proposed type of climate engineering for reducing some of the impacts of climate change. It would involve reflecting a small amount of sunlight back out into space in order to cool the planet. Proposed examples include using salt water particles to make clouds brighter and putting reflective particles, such as sulphur dioxide or calcium carbonate, into the upper atmosphere.

For more information, click here.

SSPs (Shared Socioeconomic Pathways)

These are a range of pathways that examine how the world might change over the next 100 years, including population, education, economic growth and urbanisation. They are used to derive greenhouse gas emission scenarios with different climate policies.

More information on each pathway can be found here (also reproduced here).

Synthetic fuels


These are liquid fuels that are not derived from crude oil. The types of synthetic fuels currently being developed, for example by Formula 1, due to be introduced in 2026, are manufactured using captured carbon dioxide, together with hydrogen obtained from sustainable electricity sources such as wind or solar.

For more information, click here.



Taxonomy regulation (EU)

The EU taxonomy is a classification system that is designed to provide companies, investors and policymakers with definitions for which economic activities can be considered environmentally sustainable.

Controversially, the taxonomy has labelled gas and nuclear energy as “green”.

For more information, click here.

TCFD (Taskforce on Climate-related Financial Disclosures)

The Financial Stability Board (FSB), an international body monitoring the global financial system, created the TCFD to develop recommendations on the types of information that companies should disclose to support investors, lenders and insurance underwriters in assessing and pricing the risks associated with climate change.

TVCM (Taskforce on Scaling Voluntary Carbon Markets)

The Taskforce on Scaling Voluntary Carbon Markets is a private sector-led initiative that has been working to scale up voluntary carbon markets to help meet the Paris Agreement goals. 

The taskforce was initiated by Mark Carney, UN Special Envoy for Climate Action and Finance and ex-Governor of the Bank of England. The taskforce has received some criticism for overestimating the amount of money that can feasibly be raised on voluntary carbon markets, and thereby placing too much emphasis on offsetting as a solution to climate change.

For more information, click here.

TCRE (Transient climate response to cumulative emissions of carbon dioxide)

TCRE is a metric that links the main cause of climate change (CO2 emissions) to temperature change. It is, therefore, key in calculating the remaining carbon budget for given temperature targets.

It was developed after scientists noticed that the CO2 levels versus temperature change curve was nearly linear.

For more information, click here.



A therm is a measure of heat. One therm is equivalent to the energy content of around 100 cubic feet of natural gas at a standard pressure and temperature.



Unabated fossil fuels

Fossil fuels that are used without significant efforts to reduce the greenhouse gas emissions produced throughout their life cycle. Emissions are released into the atmosphere without making efforts to capture or reduce these pollutants.

For more information, click here.


The United Nations Environment Programme (UNEP) is the global leading environmental authority. UNEP aims to strengthen environmental standards and practices at local, regional and global levels. Its work focuses on helping countries transition to low-carbon and resource-efficient economies, safeguarding ecosystems, providing evidence-based data to inform policy decisions, and fostering international collaboration on climate change.

UNFCCC (United Nations Framework Convention on Climate Change)

The UNFCCC is an international treaty that came into force on 21 March 1994. It has near-universal membership with 197 countries (Parties to the Convention) and aims to prevent “dangerous human interference” with the climate system. 



A term used in the oil and gas industry to describe processes associated with production, such as exploration and drilling (as opposed to downstream, which is processes associated with the distribution and sale of products).



VRE (Variable renewable energy)

This refers to the output from renewable energy technologies such as solar and wind power, which varies according to weather conditions. Variability is sometimes referred to as intermittency, although this implies that solar/wind projects can only ever be ‘on’ or ‘off’, rather than experiencing fluctuating output depending on changes in sun or wind intensity. Variability is, therefore, seen as the more accurate description.

VCM (Voluntary Carbon Market)

This is where carbon offset credits are bought and sold by individuals, companies and organisations to mitigate their GHG to become carbon neutral/net zero. They are not compelled to buy offsets, but they choose to do so.

Markets are facilitated by certification programmes.

See also ‘Carbon offsets’ and ‘Carbon markets’.

VCMI (Voluntary Carbon Markets Integrity Initiative)


This is an initiative to drive participation in voluntary carbon markets.

For more information, click here.



World Energy Outlook

This report is published every year by the IEA and includes detailed information and statistics about global energy trends, including supply, demand and the various production technologies.

WEO Scenarios (World Energy Outlook Scenarios)

Scenarios used by the IEA:

For more information, click here.

Working Groups

These refer to the IPCC groups that report every six to seven years on the latest scientific understanding of climate change.

WGI – Working Group One reports on the physical science of climate change.

WGII – Working Group Two reports on climate impacts. 

WGIII – Working Group Three reports on mitigation.