Climate Change Glossary

By Andy

While we can see the effects of global heating in real-time, technical language can make it difficult to understand what’s happening to our planet. We’ve put together this climate change glossary to explain technical terms and concepts associated with global heating. Use this climate change glossary as a reference for terms you find in news articles.

Note: Some terms in this climate change glossary go by other names. For instance, you might hear some people refer to “global average temperature” as “global surface temperature.” We’ve tried to include common synonymous terms in this climate change glossary wherever possible.


Assigned Amount Unit (AAU)

An Assigned Amount Unit (AAU) is the equivalent of one metric tonne of CO2. Each Annex I country determines its CO2 output in AAUs, up to a limit (the assigned amount).


Adaptation describes activity (human or natural) that responds to global warming. It is essential to cope with climate change and may refer to direct actions such as reforestation and economic activities like reducing reliance on fossil fuels.

Adaptation Fund

A program set up to help developing countries hit by climate change. Developing countries are often the worst affected and the least able to cope with global warming.

Adaptive Capacity

A region’s ability to respond effectively to the consequences of climate change.


Aerosols are solid or liquid particles that linger in the atmosphere. Aerosols containing CFCs can cause significant damage to the planet’s ozone layer and were widely banned worldwide after the Montreal Protocol in 1987.


Afforestation is the practice of planting trees in areas where forests don’t naturally occur. Poor-quality land such as tundra may need preparation before afforestation can begin.

Ancillary Benefits

Ancillary benefits are local benefits of improved climate policies, e.g., cleaner air in large cities after bans or taxes on private vehicles.

Annex I Countries

Nations that signed the Kyoto Protocol were divided into Annex 1 and Annex 2 countries. They refer to wealthy, industrialized countries and countries on the way to developing a functional market economy.

Annex II Countries

Annex II countries are a subgroup of Annex I signatories of the Kyoto Protocol. Annex II countries undertook a responsibility to provide aid to developing countries to help combat climate change.

Anthropogenic Climate Change

This term refers to climate change that humans cause. Climate changes occur naturally over long periods and can have a devastating impact on their own. Still, the present changes are referred to as anthropogenic because they result from human activity.


The Alliance of Small Island States. Many small island nations are especially vulnerable to the consequences of climate change, such as rising sea levels.


The IIRC published the 4th Assessment Report (AR4) on climate change in 2007. It found at least a 90% chance that increasing global temperatures resulted from human activity.


The IIRC published the 5th Assessment Report (AR5) on climate change in 2013-14. It found at least a 95% chance that global warming since the 1950s resulted from human activity.


Bali Action Plan

A 2007 plan to advance the work done by the Kyoto Protocol. It defined long-term global goals for combating global warming.

Bali Roadmap

The Bali Roadmap defined deadlines for Annex I countries to cut emissions and those working on the Bali Action Plan. It also introduced the Adaptation Fund.


Any fuel made from organic matter that is produced by plants, e.g., alcohol or soybean oil.

Black Carbon

The by-product of burning fossil fuels, including soot and charcoal. Black carbon absorbs sunlight and re-emits it as radiation, producing an extremely harmful aerosol.

Business as Usual

A term used to describe what would happen to the Earth’s climate if no action was taken to mitigate global warming.


Many of the terms in this climate change glossary refer to carbon. Carbon is a naturally occurring element with many molecular compounds, but when we talk about carbon emissions in this climate change glossary, we’re talking about carbon dioxide (CO2) or CO2 equivalent. See the definitions of these terms below in our climate change glossary. 

Cap and Trade

Businesses and nations can use the “Cap and Trade” system to buy or sell emissions allowances. This means paying money to another party well below its emissions target to use their “extra capacity.”

Capacity Building

This term means helping developing countries increase their capacity to withstand the effects of global warming and address local causes.

Carbon Capture

See Geological Sequestration in the climate change glossary.

Carbon Dioxide (CO2)

A naturally occurring gas. It is emitted by living organisms, including humans, and absorbed by plants. It is also produced in large volumes by burning fossil fuels. High levels of this gas cause significant disruptions to the Earth’s climate.

Carbon Dioxide (CO2) Equivalent

The standard by which the six greenhouse gases named by the Kyoto Protocol are measured. CO2 is defined as “one” over a period of 100 years, and the danger posed by other greenhouse gases is described relative to this. For example, methane is defined as 25 over the same timescale.

Carbon Footprint

The amount of CO2 or equivalent emitted by an individual, organization, nation, or process in a given period.

Carbon Intensity

The carbon emissions per unit of GDP by a nation.

Carbon Leakage

The climate change glossary defines this as when emission-producing industry from countries with stronger environmental regulations relocates to countries with weaker regulations.

Carbon Neutral

Carbon neutral describes the state where an individual, organization, nation, or process produces zero net CO2.

Carbon Offsetting

Similar to “Cap and Trade” (see the climate change glossary entry above). It means investing in or supporting emission-reducing schemes elsewhere without directly reducing your emissions.

Carbon Sink

A carbon sink is a mechanism that removes CO2 from the atmosphere. Besides the ocean, plants are our largest carbon sink, with the rainforests on land and phytoplankton in the ocean providing the greatest contributions.

Carbon Tax

A tax on companies relative to their emissions.


See Methane in the climate change glossary.

Certified Emission Reduction (CER)

A trading credit used in emission trading schemes. Defined in ERUs.


Chlorofluorocarbons are harmful gases traditionally used in applications like refrigeration and aerosol propellants. These chemicals aren’t destroyed in the troposphere and drift into the stratosphere and the ozone layer, where they cause huge damage. They are being phased out since the Montreal Protocol (see Aerosol in the climate change glossary).

Clean Coal

When coal is burned without CO2 emissions due to technological innovations. It is currently too expensive for widespread use.

Clean Development Mechanism (CDM)

A program that allows wealthier nations to achieve carbon offsetting.

Climate Change

Changes in the Earth’s climate, measured over time. These can be natural or man-made and have diverse effects, from global warming to mass extinctions to Ice Ages. The phenomenon of global warming is caused by man-made climate change.

Coral Bleaching

The paling and eventual death of coral reefs, which results from dramatic changes in their local environments. 


The frozen component of the Earth’s surface (including submerged ice). It includes glaciers, ice sheets, ice caps, and permafrost.



The removal of large areas of forest to make room for farmland or habitation.


Desertification happens when land in arid or semi-arid climates is made unusable by adverse climate conditions.


When rainfall is well below normal levels, local water sources deplete and lead to drought. Drought can have ruinous effects on local ecosystems and contribute to wildfires.


Emission Reduction Unit (ERU)

Defined as one metric tonne of CO2 equivalent. Used in CER and equivalent to an AAU.

Emission Trading Scheme (ETS)

Any scheme set up to enable a Cap and Trade system.


A measured quantity of greenhouse gases released into the atmosphere over a measured period.

Eustatic Sea-Level Change

Measurement of global sea levels rising or falling caused by the volume of water in the oceans. This is usually the system used by climate scientists to measure sea levels and can be affected by the density of water in the oceans. I.e., ice is denser than water, and so melting ice causes eustatic sea-level increase.


Feedback Loop

A process where the results of any form of climate change further exacerbate that pattern. For example, melting ice caused by global warming means less white ice to reflect the sun’s rays. This contributes to increased global warming, which further melts the ice.

Food Insecurity

When the food-producing or acquisition capacity of a nation or region is insufficient to feed the local population. This can be caused by events like desertification or the inability to afford to buy food from food-rich areas.

Fossil Fuels

Fossil fuels are natural resources that form within the Earth. Oil, coal, and natural gas are fossil fuels. They release massive amounts of CO2 into the environment when burned for fuel.

Fugitive Fuel Emissions

Fugitive fuel emissions are greenhouse gases released as a by-product of loss or waste when mining, storing, or transporting fossil fuels. 



The major bloc of developing nations in terms of climate negotiations. Often called the G77+1 when China is included.


Geoengineering is the attempt to directly stabilize the Earth’s climate by intervening in its energy balance.

Geological Sequestration

Injecting CO2 into underground reservoirs or formations.

Global Average Temperature

Also referred to as global surface temperature. This is the average temperature of the Earth’s surface over any given period.

Global Energy Budget

Global energy budget refers to the balance between incoming energy from the Sun and outgoing energy from the Earth. These must be roughly equivalent to stabilize the climate.

Global Dimming

Global dimming is a reduction in visibility, likely caused by aerosols in the local atmosphere. This is more common in larger cities.

Global Warming

Also called global heating, global warming refers to the continuing increase in the Earth’s surface temperature due to man-made activities.

Global Warming Potential (GWP)

The metric used to describe how dangerous greenhouse gases are (see CO2 equivalent).

Greenhouse Gases (GHGs)

A group of six gases that contribute to global warming at higher levels. These are carbon dioxide, nitrous oxide, hydrofluorocarbons, methane, perfluorocarbons, and sulfur hexafluoride.

Greenhouse Effect

This term refers to the warming effect caused by excessive amounts of greenhouse gases in the atmosphere. It forces energy to remain trapped on Earth, which causes heating.


Hot Air Argument

An argument that warns against governments meeting their Kyoto Protocol targets and then using ERUs to flood the market.

Hydrofluorocarbons (HFCs)

Like CFCs, these are potent greenhouse gases. However, they are still used as a substitute for CFCs in many industries.


Ice Cap

A mass of ice that covers a highland area.

Ice Sheet

A mass of ice that covers an area of land. The Arctic and Antarctic ice sheets are the largest ice sheets on Earth and constitute most of the ice on the planet.

Ice Shelf

The part of an ice sheet that sits on the water.


The Intergovernmental Panel on Climate Change. This body reviews research on climate change and informs intergovernmental policy and decision-making.


Joint Implementation

Like the CDM, this allows wealthier nations to acquire carbon credits by investing in less-developed countries’ programs to reduce emissions. 


Kyoto Protocol

TheKyoto Protocol is a foundational document in the global fight against climate change. It set binding targets for reducing emissions for participating countries.



This stands for land use, land-use change, and forestry. This covers positive action on afforestation and reforestation or curbing the impact of deforestation (see definitions elsewhere in the climate change glossary).



A potent hydrocarbon and greenhouse gas. Methane occurs naturally but is also produced by anaerobic decomposition (decomposition without oxygen).


Mitigation describes any action taken to limit the impact of climate change.


Natural Greenhouse Effect

The layer of naturally occurring greenhouse gases that keep energy inside the Earth’s atmosphere. This layer enables temperatures on Earth to remain stable enough for life to exist.

Non-Annex 1 Parties

These parties are the developing countries that have ratified the Kyoto Protocol but are not bound by its restrictions.


Ocean Acidification

Ocean acidification is caused by excess carbon build-up in the ocean. When CO2 dissolves in the ocean, it forms carbonic acid. This contributes to coral bleaching and creates difficult conditions for much sea life.


Ozone is a gas that occurs in the troposphere and stratosphere. Tropospheric ozone is harmful in high concentrations, but stratospheric ozone mediates the balance of radiation from the sun.

Ozone Layer

A dense layer of ozone in the stratosphere. This is depleted by harmful man-made aerosols, including chlorine and bromine compounds. The ozone layer suffered significant damage before the regulation of CFCs, and there is still an ozone hole above the Antarctic.


Per-Capita Emissions

Per-capita emissions are a nation’s emissions level per head of the population.

Permian-Triassic Extinction Event

Also known as the Great Dying, the Permian-Triassic was the largest extinction event in known history (approx. 251.9m years ago). It was probably caused by the excessive release of CO2 and methane (see the relevant entries in the climate change glossary) when fossil fuels in the Siberian Traps burned. Roughly 57% of all biological families went extinct, and it serves as a stark reminder of the need to balance the greenhouse effect.


Phytoplankton are minuscule plants that form the basis of the ocean food web and are an important carbon sink.


Stands for parts-per-million. The IPCC advises that greenhouse gas levels (measured at CO2 equivalent) must be below 450ppm to prevent dangerous climate change. However, many scientists and countries at the highest risk suggest that 350ppm is preferable.

Pre-Industrial Levels of Carbon Dioxide

The level of CO2 equivalent in the atmosphere before the Industrial Revolution. Estimated to be around 280ppm.


Renewable Energy

This term describes the energy provided by non-fossil fuel sources such as wind or solar power.


The process of replanting trees in areas that have experienced deforestation.


Any part of the climate system that can store and potentially release greenhouse gases.



The outer part of the Earth’s atmosphere.

Sustainable Development

Development that doesn’t contribute to global warming.


Technology Transfer

The sharing of technological developments between countries to combat global warming.

Thermal Expansion

In climate change terms, this describes the increase in the volume of the oceans caused by melting ice.


The lower part of the Earth’s atmosphere.


Ultraviolet (UV)-B Radiation

This is solar radiation, mostly absorbed by the ozone layer, that has adverse effects on life in the absence of ozone.


The United Nations Framework Convention on Climate Change aims to avoid excessive interference with the Earth’s climate (this may extend to geoengineering attempts).


Water Stress

This event happens when an area has insufficient access to fresh water for continued development.

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