Fine suspended particles that may persist for days to years depending on their composition and height in the atmosphere; except for black carbon, aerosols reflect incoming sunlight and have a cooling effect. See global dimming.

The planting of forests on a piece of land that has not held forests for 50 years or longer. See reforestation.

The addition of trees to landscapes that have been dominated by agriculture.

The reflectivity of the Earth, which indicates the fraction of incoming sunlight that does not warm the atmosphere, land, or oceans, but is instead reflected directly back to space.

Alley cropping
The combining of agriculture and tree crops on the same land.

A habitat or condition in which oxygen is lacking or only present in trace amounts.

Anaerobic biodigesters
Tanks of varying design that hold decomposing organic matter in the absence of oxygen, provide habitat for methanogens, and allow buildup and collection of methane gas. See methanogens.

The proposed name for a geological epoch beginning approximately now; it is based on the notion that human activities have dramatically altered the atmosphere, hydrology, and biosphere components of the Earth system. See Holocene.

Attribution science
A subfield of climate science concerned with determining the extent of human influence on various aspects of climate change, including specific extreme events.

Big Green
A rubric given to large, financially robust organizations that historically have led advocacy for all aspects of environmental protection in the US, including climate change.

Carbon-rich product made by heating biomass in environments that are low in oxygen; they are applied to soils to enhance their carbon content.

A type of biofuel produced from soybeans, canola, and other crops, and from waste materials such as cooking grease; it is used as a supplement or replacement for petroleum diesel.

Bioenergy with carbon capture and storage (BECCS)
An emerging technology for removing carbon from the atmosphere in which biomass is burned for electricity generation or converted to useful products, and the carbon dioxide emissions are captured and then geologically sequestered.

Gas that emanates from landfills and other anaerobic habitats that is made up of a roughly 50:50 mixture of carbon dioxide and methane.

Biological pump
A process by which carbon is buried in the deep ocean; it involves the uptake of carbon by microorganisms at the ocean surface and is followed by the sinking of that carbon into the ocean depths when the organisms die.

Black carbon
Nearly pure carbon aerosol produced by burning petroleum diesel fuel and biomass that arises from forest fires; unlike other aerosols, it acts as a strong driver of global warming.

Blackbody radiation feedback
A type of negative climate feedback in which Earth radiates out increasing amounts of heat as it warms, dampening the effects of global warming.

Blue carbon
Carbon that is captured and trapped in coastal and marine ecosystems, including mangroves, tidal marshes, seagrasses, and sediments.

Border carbon adjustment
Found in carbon tax proposals, a tariff imposed on carbon-rich fuels and commodities imported from countries that do not price carbon; it can also refer to credits provided to US firms that export carbon-rich goods to countries that do not price carbon.

Cap and trade
A type of carbon pricing system in which government sets an overall and continuously decreasing emissions cap for industries under its jurisdiction; the industries acquire allowances that permit them to emit carbon dioxide, which can be traded in regulated markets.

Capacity factor (electricity)
The percentage of time that a power plant generates electricity, equivalent to the fraction of the total power that would be produced if the plant were always operating.

A class of molecules found in all cells, which contain carbon, hydrogen, and oxygen atoms; includes both simple sugars and large polysaccharides such as starch; formed during the process of photosynthesis in plants and some microorganisms.

Carbon bubble
A financial term that refers to the dollar amount of overinvestment in fossil fuel development that may never yield an economic payoff.

Carbon budget
An outcome of climate modeling studies, describing the amounts of carbon that can be emitted to the atmosphere while still meeting targets for 1.5ºC or 2ºC worlds.

Carbon capture and storage (CCS)
Technology for trapping carbon dioxide from the smokestack emissions of electric power plants and manufacturing facilities, followed by the transport and burial of the carbon dioxide in deep underground geologic reservoirs.

Carbon capture and utilization (CCU)
Technology for trapping carbon dioxide from the smokestack emissions of electric power plants and manufacturing facilities, followed by sale and use of the captured carbon for various purposes. See enhanced oil recovery.

Carbon cycle
A general term describing how carbon-containing molecules, in gas, liquid, or solid forms, are transferred among the atmosphere, land and oceans; this cycle works on both slow and fast timescales and includes the deep underground when considered over very long periods of time.

Carbon dioxide
A greenhouse gas with the chemical formula CO2, a by-product of burning fossil fuels, and present at low but increasing levels in the atmosphere; it persists for exceptionally long periods of time in the atmosphere.

Carbon dioxide equivalent (CO2(e))
For a specified timeframe, such as 20 or 100 years, the amount of greenhouse warming produced by emitting one ton of a greenhouse gas, expressed as a multiple of the warming produced by emitting one ton of carbon dioxide.

Carbon dioxide fertilization
A phenomenon by which trees and other vegetation grow faster when atmospheric carbon dioxide levels are elevated, since uptake of carbon dioxide is a key aspect of photosynthesis.

Carbon intensity
A number that indicates how much carbon dioxide is emitted to the atmosphere from production, transport, and use of an alternative fuel, compared to the amount of carbon dioxide emitted when traditional fossil fuels are the source of energy.

Carbon monoxide
A hazardous byproduct of the incomplete combustion of fossil fuels and biomass, with the chemical formula CO.

Carbon negative
A term referring to a technology or process by which carbon dioxide is removed from the atmosphere. See negative emissions technology.

Carbon offsets
Found in cap and trade carbon pricing programs, a way for regulated industries to meet a portion of their obligation to reduce emissions by investing in decarbonization projects outside of the program’s jurisdiction.

Carbon tax
A price levied by government on carbon dioxide emissions, intended to force emitters to pay the human and environmental costs of their pollution, and to provide a relative boost to carbon-free energy sources.

Cellulosic ethanol
Ethanol that is manufactured by fermentation from any number of non-food crops or other sources, such as switchgrass, municipal solid waste, or agricultural residues left after harvesting.

An aspect of weather that is a consequence of its dynamic and irregular behavior, and reflected in an extreme sensitivity to small perturbations, which makes it impossible to predict weather further than two to three weeks into the future.

Chemical weathering feedback
A type of negative climate feedback in which greenhouse warming and the resulting higher precipitation in turn lead to increased uptake of atmospheric carbon dioxide by rocks on the Earth’s surface.

Chlorofluorocarbons (CFCs)
An exceptionally potent class of manmade greenhouse gases that contain carbon joined to both chlorine and fluorine atoms; they are banned by international treaty because of their reaction with stratospheric ozone. See ozone hole, ozone layer.

A class of molecules found in plant cells that are able to absorb incoming sunlight, and then use that energy to drive the process of photosynthesis.

Circular carbon economy
A term for a future energy economy in which carbon is obtained by removing carbon dioxide from the atmosphere; reaction of this sequestered carbon dioxide with renewable hydrogen then produces energy-rich fuels that return carbon dioxide to the atmosphere when burned.

Clean energy standard
A government mandate requiring that increasing amounts of electricity be generated from carbon-free or very low-emitting energy sources, such as hydropower, solar, wind, and nuclear power. See renewable portfolio standard.

Average weather conditions over a year or longer, either globally or with respect to specific geographic regions. See weather.

Climate change drivers
Natural or anthropogenic influences that alter the heat balance of the Earth with respect to its surroundings in space; different drivers act to either raise or lower the Earth’s average surface temperature; also called radiative forcings.

Climate feedbacks
Earth system processes that either amplify (positive feedback) or diminish (negative feedback) the effects of climate change drivers.

Climate inertia
A feature of Earth’s climate system that causes the impacts of anthropogenic climate change to persist over long periods; it arises from the exceptionally long lifetime of carbon dioxide in the atmosphere.

Climate model
A computer representation of all or part of Earth’s climate system that is useful for projecting the future effects of anthropogenic and natural climate change drivers.

Climate proxies
Certain observable parts of the Earth system such as ice cores, tree rings, and ocean sediments, that can be analyzed to yield information about past climates, including temperatures and composition of the atmosphere.

Climate sensitivity
The increase in Earth’s average surface temperature caused by doubling of atmospheric carbon dioxide concentration compared to pre-industrial levels, designated DT2x.

The use of leftover heat from electric power generation to provide energy for other processes, such as building heating or air conditioning; alternatively, the use of excess heat to generate electricity.

A nearly pure carbon product that results from heating coal to very high temperatures in ovens, in the absence of oxygen, which allows removal of impurities to generate a product useful in steelmaking and other applications.

Community solar
A growing model for solar power in which individuals and groups in a local area share both the electricity generated from a common installation and the savings from returning excess power to the grid.

Concentrated animal feeding operations (CAFO)
Factory farms in which large numbers of livestock are housed together in a small area; these are large sources of climate, air and water pollution.

Concentrating solar thermal power
Large facilities that funnel sunlight from an array of collectors to a central tower, where a circulating liquid is heated to provide the energy to generate electricity.

Conservation easement
Legal agreement that protects a land parcel by transferring rights to an organization or government, yielding environmental protection and climate benefits, and preventing exploitative use.

Conservation tillage
A method for working agricultural land that retains more carbon in the soil.

Corn ethanol
Ethanol produced from the corn crop by fermentation, primarily used for blending with gasoline.

Cover crops
Crops that are planted on agricultural land to protect the health of the soil and conserve biodiversity, rather than harvesting.

The portion of the Earth’s climate system that consists of ice, including sea ice, ice shelves, and glaciers and ice sheets in Greenland, Antarctica, and high mountains around the world.

Dansgaard-Oeschger (D-O) events
Abrupt increases in temperature followed by gradual cooling, which occurred during the last Ice Age glaciation about 15,000 to 70,000 years ago.

Deep Decarbonization
A term describing the process by which the energy economy is largely or entirely converted from reliance on fossil fuels to low-emitting or carbon-free power sources.

Clearing of forest land to allow for urbanization, pastures, agriculture, or other uses; deforestation returns forest carbon to the atmosphere and shrinks the land sink for carbon, worsening global warming.

The deliberate shrinking of global or national economies with the goal of limiting global warming.

Demand response
In electricity markets, changes to the timing of electricity use by consumers to better match power supply on the grid; includes home solar panels and batteries as a way of minimizing grid reliance.

A broad term describing the degradation of land in regions of water scarcity, including declines in economic productivity, soil richness, and biodiversity.

Diesel fuel
A liquid fuel product consisting of large hydrocarbons and derived from refinement of crude oil; it is used in industry and transportation, especially aviation, shipping, and long-haul trucking.

Direct air capture
A developing industrial technology for removing carbon dioxide directly from the atmosphere.

Discount rate
A way of estimating future costs of climate change; lower discount rates mean more value is placed on the future climate, thus implying that large investments in mitigation should be made today. See intergenerational equity, social cost of carbon.

The extent to which it is possible to readily adjust the amount of power provided by primary energy sources that generate electricity, which is valuable due to the need to match supply with demand on the grid.

Distributed solar
Small photovoltaic solar sources that serve individual residences or local communities, reducing consumers’ reliance on the larger grid.

The perspective that climate change is unsolvable and will certainly wreak havoc on global society.

Radiation in the low-energy infrared portion of the electromagnetic spectrum, which is emitted by the Earth to maintain the heat balance with its surroundings in space.

Conversion of industry, residential, transportation and commercial energy end uses from fossil fuels to electricity.

Endangerment finding
Under the federal Clean Air Act, a statement by the Environmental Protection Agency that a particular pollutant causes harm to human health and the environment; triggers the process of regulating that pollutant.

Energy balance
A condition that occurs when the amount of incoming solar radiation equals the amount of outgoing Earthlight, producing a constant overall temperature; small naturally occurring imbalances are dwarfed today by imbalances generated by human activities.

Energy crops
Food crops, grasses, or fast-growing trees that are grown for the purpose of generating fuel rather than food.

Energy-economy models
Computer representations of regional, national, or global energy systems that are able to project future energy use and prices arising from different climate policy choices.

Energy storage
Set of technologies including batteries and pumped storage of hydropower, which provide ways to capture electrical energy for later release; they are essential for accommodating intermittent wind and solar power on the grid.

Enhanced oil recovery
The injection of carbon dioxide captured from power and manufacturing plant emissions streams into oil wells; this pressurizes the wells and allows extraction of more oil.

Enhanced weathering
A method for directly capturing carbon dioxide from the atmosphere, involving crushing and spreading out of large amounts of rock, to speed the natural weathering process. See weathering.

A process in which lakes and other small water bodies are overgrown by algae and other organisms, depleting the water of dissolved oxygen; this is typically caused by excess runoff of nutrients from land.

Excise tax
Taxes that are imposed by governments on specific products, such as cigarettes, alcohol, and gasoline; the tax is paid by the manufacturer, who then passes the extra cost on to consumers.

A cost or benefit that is absorbed by or conferred upon third parties.

Feedback loop
In Earth’s climate system, a process by which the effects of an initial energy imbalance are either dampened (negative feedback) or amplified (positive feedback). See blackbody radiation feedback, ice albedo feedback, water vapor feedback.

Production of ethanol from the carbohydrates in food crops or cellulosic biomass through the action of yeast in an environment lacking oxygen.

Fixed carbon
Carbon that is found in large molecules in the solid portions of the Earth and biosphere, or that is dissolved in the liquid portions of living cells.

A process to extract oil and gas by forcing large amounts of sand, water, and chemicals into underground deposits; this fractures the rocks and allows recovery of much greater amounts of fuel as compared to conventional drilling.

Free-rider problem
A market failure that happens when bystanders benefit from actions that others have taken.

Fuel cell
An efficient device able to convert the chemical energy in hydrogen or other fuel directly into electricity.

Generation capacity
The maximum amount of power that an electricity-producing facility is able to provide.

A general term referring to approaches to artificially alter Earth’s energy balance at large scale, including methods for atmospheric carbon removal and for reducing the amount of solar radiation that reaches the planetary surface. See carbon negative, marine cloud brightening, sulfur aerosol injection.

Global commons
A shared planetary resource that provides critical environmental benefits, such as the atmosphere, oceans, cryosphere or rain forests.

Global dimming
A phenomenon referring to the cooling of Earth’s surface caused by the reflection of sunlight by atmospheric aerosols; this arises from either volcanic eruptions or human activities, especially fossil fuel burning.

Global warming potential
The ratio of the amount of heat trapped by one ton of a greenhouse gas to the amount trapped by one ton of carbon dioxide.

Green bank
A bank dedicated to increasing the amount of private investment in climate-friendly practices and technologies.

Green gentrification
An unintended consequence of climate-friendly urban practices, in which low-income or other vulnerable communities are priced out of desirable neighborhoods.

Green New Deal
The vision for a socially just, renewable energy transition advanced in early 2019 by Democrats in the US House of Representatives.

Greenhouse gas
Atmospheric constituent able to absorb infrared radiation emitted by the Earth, trapping a portion as heat and thus warming the surface. See Earthlight.

Greenhouse effect, anthropogenic
The augmentation of the natural greenhouse effect caused by atmospheric buildup of carbon dioxide, methane, and other greenhouse gases as a consequence of human activities.

Greenhouse effect, natural
A feature of Earth’s climate system that refers to the ability of atmospheric water vapor, carbon dioxide, methane, and some other gases to absorb outgoing Earthlight and radiate it back to Earth, warming the surface.

Gross Domestic Product (GDP)
A measure of the total economic activity of a nation over a specified time period, calculated from the market value of goods and services produced; it is used as a benchmark to compare the overall health and sizes of economies.

Haber process
Industrial operation that yields ammonia for fertilizers by combining natural gas with atmospheric nitrogen at very high temperature and pressure.

Hadley cell
A cyclical atmospheric flow pattern involving the rise of warm moist air at the equator and return of dry air to the surface in subtropical latitudes, where most deserts are found.

A class of organic molecules that contain carbon joined to one or more of the halogen atoms, the most important of which are chlorine and fluorine; HFCs and CFCs are both halocarbons.

Heat capacity
The amount of heat that has to be supplied to a given amount of a substance in order to bring about a temperature increase of one degree Celsius.

The geologic epoch that began at the end of the last Ice Age, about 11,700 years ago, and is still in existence. See Anthropocene.

Hothouse Earth
A stable climate state in which temperatures are far warmer than today, most or all of the cryosphere has melted, and sea levels are much higher.

Hydraulic fracturing
See fracking.

Molecules solely made up of carbon and hydrogen atoms linked together by chemical bonds; hydrocarbons make up the vast majority of coal, oil and natural gas deposits.

Hydrofluorocarbons (HFCs)
A class of manmade chemicals containing carbon joined to fluorine atoms and used in refrigeration and other applications; these function as exceptionally potent greenhouse gases when released to the atmosphere.

A light, energy-dense fuel with the chemical formula H2 that is presently produced from natural gas, but also potentially synthesized from carbon-free energy; it is useful as a replacement for natural gas or to provide long-term energy storage capacity on the electricity grid.

Hydrological cycle
The movements of Earth’s water through the land, ocean, and atmosphere, including evaporation, precipitation, runoff, and underground percolation.

Ice albedo feedback
A positive feedback loop in which melting of snow and ice exposes a darker land or ocean surface, which leads to amplification of warming because the new, darker surface has lower albedo and absorbs more sunlight. See albedo.

Ice core
A cylindrical sample of ice taken at the surface of a glacier or ice sheet and extending to a depth of up to several miles.

Ice shelf
A section of ice that extends from a land ice sheet to float on the adjacent region of ocean.

Infrared radiation
Low-energy light that is emitted naturally by the Earth; it makes up the outgoing component of the heat balance that maintains Earth’s average surface temperature.

Intergenerational equity
A principle of justice holding that future generations have equivalent rights of access to natural resources and to a stable climate system.

Intergovernmental panel on climate change (IPCC)
International scientific body created in 1988 by mandate of the United Nations; it provides government-approved, regular comprehensive reviews of climate science, including possibilities for mitigation and adaptation to climate change.

Investor-owned utilities (IOUs)
Privately owned companies that distribute electricity and may also own significant amounts of electricity infrastructure and generation capacity.

A class of chemical compounds emitted as gases into the atmosphere by certain kinds of trees, which react in the atmosphere to form the greenhouse gas ozone.

Distinct forms of chemical elements that contain the same number of protons but different numbers of neutrons in their nuclei; they are useful in radioactive dating of environmental samples and in establishing whether these samples are of mineral or biological origin.

Kaya Identity
An equation that relates global warming emissions to population, economic activity, and the carbon intensity of energy production.

Kyoto protocol
An international environmental treaty enacted to reduce global warming that went into effect in 2005, but was never ratified by the United States.

An increase in greenhouse gas emissions that occurs elsewhere in the world due to climate policy enacted in a particular state or nation.

Levelized cost
A measure of the cost of electricity generation for a particular source that accounts for both construction and operation over the full life of the facility.

Lifecycle analysis
A method to calculate the total greenhouse gas emissions from the production and use of a commodity, which is often applied to estimate the climate costs and benefits associated with the use of biomass as a substitute for fossil fuels.

A substance in plants and trees that helps create dense, tough tissues, thus making it more difficult to break down the plant for production of cellulosic ethanol.

Liquefied natural gas (LNG)
Natural gas that has been extracted, refined, and cooled under pressure to generate a liquid form of the fuel that is suitable for export on dedicated large ships.

Low carbon fuel standard
A state law in California and Oregon that requires steady reductions in the carbon content of fuels used for transportation, promoting the growth of sustainable biofuels and electrification.

Marginal cost
In economics, the increment in cost that comes from producing one additional unit of a good or service.

Marine cloud brightening
A geoengineering approach to bring about global cooling, in which sea salt is sprinkled on clouds that form over the oceans, causing them to reflect more sunlight. See geoengineering, sulfur aerosol injection.

Mass timber
A construction style for buildings in which wood rather than concrete is the primary material, which often uses prefabricated, engineered components assembled on site.

Metallurgical coal
The relatively small and high-grade portion of the coal reserve that is used to produce coke, a carbon product that is employed in turn to make steel. See coke.

A potent greenhouse gas with the chemical formula CH4, and the principal constituent of natural gas deposits, which is presently increasing in atmospheric concentration due to human activities.

Methane hydrates
A large fossil fuel resource consisting of methane in a solid crystalline form that includes caged water molecules and is found on seafloors and in other marine sediments.

A class of microorganisms that generate all the biologically-derived methane on Earth; they occur naturally in habitats lacking oxygen, including those created by human activities, such as landfills, cattle gut, and rice paddies.

A small, localized group of electricity generation sources that can function either independently or in connection with the larger regional grid.

Milankovitch cycles
Repeating periods of time during which the amount of sunlight reaching the Earth’s surface varies predictably; caused by the way Earth’s orbital movements are influenced by the sun, moon and planets, and giving rise to regular variations in climate such as the Ice Ages.

Nationally Determined Contributions (NDCs)
Under the international Paris Agreement, individual country pledges for how steeply greenhouse gas emissions will be reduced over time, and how those reductions will be achieved.

Natural gas
A mixture of gaseous hydrocarbons consisting primarily of methane, and found trapped in the pores of sedimentary rocks.

Natural gas liquids
A collective term for a group of small hydrocarbons that includes ethane, propane and butane.

Negative emissions technology
A general term for large-scale approaches for removing carbon from the atmosphere, including direct air capture, bioenergy with carbon capture and storage, afforestation, and sequestration in agricultural soils. See carbon negative.

Net metering
A way of pricing electricity in which consumers with home solar panels receive credit for returning extra power to the grid at the same rate that is charged by the utility.

Net primary productivity
A measure of the amount of fixed carbon generated by photosynthesis, which also accounts for the carbon returned to the atmosphere by respiration. See photosynthesis, respiration.

Nitrogen cycle
A general term describing how nitrogen-containing molecules in gas, liquid, or solid forms are transferred among the atmosphere, land, and oceans; human activities, especially agriculture, have greatly perturbed the natural operation of the cycle.

Nitrogen fixation
A key step in the nitrogen cycle by which atmospheric nitrogen is taken up by certain classes of microorganisms, including those colonizing the roots of leguminous plants.

Nitrogen oxides
A class of chemical compounds that contain nitrogen joined to one or more oxygen atoms; the abbreviation NOx designates a mixture of these compounds.

Nitrous oxide
An extremely potent greenhouse gas with the chemical formula N2O; it is naturally present at trace levels in the atmosphere and presently increasing in concentration due to human activities, especially agriculture.

Non-methane volatile organic compounds (NMVOC)
The designation for a group of carbon-containing gases generated as byproducts of combustion and other industry processes that contribute to forming ground-level ozone.

Notice and comment
An administrative law process in which state or federal government agencies provide the opportunity for members of the general public to offer their opinions about new regulations before they are enacted.

Nuclear fission
Commercial technology for electricity generation in which a uranium isotope is split into smaller particles, thus releasing large amounts of energy.

Nuclear fusion
The process by which certain isotopes of hydrogen are joined to make helium, thus releasing large amounts of energy.

An extremely potent greenhouse gas with the chemical formula O3; the ozone in the stratosphere protects Earth’s biosphere from damaging ultraviolet radiation, while ozone in the troposphere is a hazardous component of smog.

Ozone hole
The name given to the depletion of the ozone layer over the continent of Antarctica where stratospheric ozone is particularly susceptible to destruction by man-made chlorofluorocarbons.

Ozone layer
A thin band of ozone present in the Earth’s stratosphere, which is naturally formed and destroyed under the influence of sunlight; it is depleted by reaction with man-made chlorofluorocarbons and recovering since these chemicals were banned in the late 1980s.

Paleocene Eocene Thermal Maximum
A climate event that occurred about 55 million years ago, in which natural carbon emissions caused Earth to rapidly warm by at least 5 degrees Celsius.

Paris Agreement
An international climate agreement in which countries pledge to decarbonize their economies in accordance with individualized roadmaps, in order to keep global warming below 2 degrees Celsius and increase resilience to climate change.

A biological process carried out by plants and some microorganisms; it involves the use of sunlight to drive the uptake of carbon dioxide from the atmosphere, and its incorporation into “fixed” carbon in the organisms’ cells. See respiration.

Photovoltaic cell
A device made of a semiconductor material that can convert incident sunlight into an electrical current.

Microorganisms that inhabit the surfaces of oceans, lakes, and other bodies of water that are able to fix atmospheric carbon by photosynthesis.

Polar vortex
The rapid counterclockwise circulation of air about the North and South poles, which helps maintain very cold temperatures in the polar regions.

Political action committee (PAC)
Organizations run by labor unions, corporations, or trade groups that may raise funds from specific groups or members of the general public, to promote the election of candidates for political office.

A legal term indicating that a higher government authority that has passed laws in a particular field may preclude lower authorities from enacting legislation in that area or may override that legislation.

Public-private partnerships
Agreements between federal or state governments and private industries in which both contribute resources and expertise to promote a new technology or other initiative.

Public trust doctrine
A legal principle which holds that sovereign governments must preserve natural resources in trust for the benefit of the general population, and for future generations.

Public utility
See investor-owned utility.

Public utility commission (PUC)
State governing bodies that supervise the work of privately owned utilities, such as electricity or water companies, ensuring that the rates charged and the services provided are in keeping with the public interest.

Radiative forcing
See Climate change drivers.

The process by which public utilities determine the price of electricity for their consumers.

Illegal discrimination in the offering of loans by banks or other lenders based on the location of the property or the race of the applicant.

Reduction (chemical)
The addition of electrons to chemical compounds as a consequence of a chemical reaction; it is often associated with the addition of hydrogen atoms and/or the removal of oxygen atoms from the compound.

The regeneration of forests on lands from which they have been recently removed.

Renewable Fuel Standard
A federal law that requires production and blending of specific volume amounts of ethanol and biodiesel into transportation fuels.

Renewable portfolio standards (RPS)
State laws that require electric utilities to procure increasing amounts of power from renewable energy sources, such as solar, wind, and geothermal. See clean energy standard.

Representative concentration pathways
Projections of how atmospheric greenhouse gas concentrations will change over time, depending on the quantities of greenhouse gases emitted; used by the Intergovernmental Panel on Climate Change to gain insight into Earth’s possible climate futures.

Reserve (fossil fuel)
The portion of a fossil fuel resource that is well-known and economically viable to develop. See resource (fossil fuel).

Reserve-to-Production Ratio (R/P)
A number that indicates the number of years that a known fossil fuel reserve will last, if extraction of the fuel continues at the same rate as in the current year.

Resource (fossil fuel)
The total quantity of coal, petroleum, natural gas or other fossil fuel that is present in a particular region, whether economically viable to develop or not. See reserve (fossil fuel).

Residence time
A measure of how long a greenhouse gas persists in the atmosphere before it is removed by natural processes.

A metabolic process in which nutrients such as fats and sugars are combined with oxygen to yield energy, producing water and carbon dioxide as byproducts; together with photosynthesis, it forms a key part of Earth’s “fast” carbon cycle. See photosynthesis.

Restructuring (electricity)
A legal and political process that introduced competition into electricity markets, for both generation of electrical power and provision of services to consumers; it partially replaces a model in which integrated, monopoly utilities performed all functions.

Revenue neutrality
A feature of tax laws by which government neither gains nor loses funds; for carbon taxes this may be accomplished by returning the revenues to households or by including offsetting tax cuts for businesses or other entities.

Riparian forest buffers
A forested land area adjacent to rivers and other waterways that provides environmental benefits and is able to filter hazardous runoff when located adjacent to agricultural land.

Shared socioeconomic pathways
Computer models of human social, economic, and political development that are useful for examining how distinctive aspects of future worlds impact the success of climate policies.

The integration of trees and grassland with animal grazing to provide mutual benefits.

A process by which a greenhouse gas is removed from the atmosphere.

Snowball Earth
Cold temperature periods in Earth’s past in which ice sheets extended over much larger portions of the surface, and sea levels were much lower than they are today.

Social cost of carbon
An estimate of the financial damage caused to society by the emission of one ton of carbon dioxide or its equivalent.

Solar battery
A home energy storage device that can be installed along with solar panels, therefore providing a source of electrical power and reducing reliance on the larger electricity grid.

Solar radiation management
A term given to a collection of proposed new technological approaches for artificially reflecting sunlight from the Earth’s surface and atmosphere with the intention to promote global cooling. See geoengineering, sulfur aerosol injection.

Stranded assets
Overinvestments in fossil fuel reserves and infrastructure that will be abandoned at a loss upon a collapse in demand for the products.

Stranded liabilities
The costs of safely retiring aging or economically nonviable fossil fuel infrastructure, including plugging old wells, as required by environmental laws.

The level of the atmosphere above the troposphere, extending from about 10 – 50 kilometers in height above the Earth’s surface.

Sulfur aerosol injection
A geoengineering approach to bring about global cooling, in which sulfur-containing particles that reflect incoming sunlight are continuously dispersed in the atmosphere. See geoengineering, marine cloud brightening.

Super PAC
A type of political action committee that is legally entitled to raise unlimited amounts of money from corporations, individuals, and other entities, as long as it does not coordinate with the candidates it advocates for. See political action committee.

Tar sands
Large West Canadian deposits of sand, clay, and water mixed with bitumen, a thick hydrocarbon mixture that can be refined into gasoline and other products.

Thermal coal
The large portion of the coal resource that is used to generate electricity.

Tidal power
Renewable energy harnessed from the movement of ocean waters in response to the gravitational pulls of the Sun and Moon.

Tipping points
Thresholds in distinct parts of Earth’s climate system where only a small amount of additional warming is enough to flip the system into a new state.

Tragedy of the commons
Where common resources are shared among many parties, the problem that develops when the self-interested actions of some users degrade the capacity of the shared resource to sustain significant use.

The escape of water from the pores (stomata) on plant leaves when they open to admit carbon dioxide and release oxygen during photosynthesis.

The lowest level of the atmosphere, extending from Earth’s surface to a height of about 10 kilometers.

United Nations Framework Convention on Climate Change (UNFCCC)
A 1994 international treaty, ratified by nearly 200 countries, that calls for preventing dangerous anthropogenic interference with the Earth’s climate system.

Water vapor feedback
A positive feedback loop in which higher temperatures allow the atmosphere to hold more water vapor, which leads to amplification of warming because water vapor is a greenhouse gas.

The dynamic fluctuations in temperature, humidity, precipitation, wind, and other physical aspects of the atmosphere pertaining to a local region of Earth’s surface.

The physical processes and chemical reactions that remove carbon dioxide from the atmosphere over many thousands of years, and incorporating the carbon into solid shells and minerals.

Wind turbine
A machine that uses the energy in wind to generate carbon-free electricity.