Skip to main content

Key Definitions and Literature Cited

About this guide

Climate Literacy: Essential Principles for Understanding and Addressing Climate Change presents information that is important for individuals and communities to know and understand about Earth’s climate, the impacts of climate change, and solutions. Principles in the guide can serve as discussion starters or launching points for learning about the climate crisis and what’s being done to address it across the world.

The guide aims to promote greater climate literacy by providing this educational and communication framework of principles and concepts.

Download the Climate Literacy Guide in PDF

All definitions are from the Fifth National Climate Assessment Glossary, unless another source is cited.

Adaptation In human systems, the process of adjustment to actual or expected climate and its effects to moderate harm or exploit beneficial opportunities. In natural systems, the process of adjustment to actual climate and its effects. Human intervention may facilitate adjustment to expected climate and its effects.

Aerosols A suspension of airborne solid or liquid particles, with typical particle size in the range of a few nanometers to several tens of micrometers. Aerosols have both natural and human-caused sources. Overall, they tend to produce cooling by scattering incoming radiation and by affecting cloud cover, although some aerosols can cause warming directly by absorbing radiation and indirectly through their interactions with clouds.

Biodiversity The variety of life, including the number of plant and animal species, other life forms, genetic types, habitats, and biomes in an ecosystem.

Carbon cycle The series of processes by which carbon compounds flow among reservoirs in the environment, such as the incorporation of carbon dioxide into living tissue by photosynthesis and its return to the atmosphere through respiration, the decay of dead organisms, and the burning of fossil fuels. In the carbon cycle, carbon flow or output from one reservoir transfers carbon to other reservoir(s).

Carbon dioxide (CO2) A naturally occurring gas, as well as a by-product of burning fossil fuels from fossil carbon deposits, burning biomass, land-use changes, and industrial processes (e.g., cement production). CO2 is the principal anthropogenic greenhouse gas that affects Earth’s radiative balance. As the reference gas against which the radiative forcing of other greenhouse gases are measured, it has a global warming potential of 1.

Carbon dioxide removal A set of techniques that aim to remove and/or sequester carbon dioxide (CO2) directly from the atmosphere by either increasing natural carbon sinks or using chemical engineering to remove the CO2.

Carbon sink Any process, activity, or mechanism that removes carbon from the atmosphere. A carbon sink may also refer to a physical location, defined area, or geological or biological element of Earth’s system (e.g., the ocean, a country, biomass) that stores acquired carbon from the atmosphere for a specified period of time.

Circulation (ocean) The large-scale movement of waters in the ocean basin. It is a key regulator of climate by storing and transporting heat, carbon, nutrients and freshwater all around the world. (NASA, 2020)

Climate Climate, in a narrow sense, is usually defined as the average weather or, more rigorously, as the statistical description in terms of the average and variability of defining factors over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation, and wind. Climate, in a wider sense, is the state, including a statistical description, of the climate system.

Climate change Changes in average weather conditions that persist over multiple decades or longer. Climate change encompasses both increases and decreases in temperature, as well as shifts in precipitation, changes in frequency and location of severe weather events, and changes to other features of the climate system. 

Climate justice Within the United States, is the recognition of diverse values and past and ongoing harms, equitable distribution of benefits and risks, and the procedural inclusion of affected communities in decision-making processes. (Adapted from USGCRP, 2023: Ch. 20)

Climate literacy An understanding of how the climate system works, how human actions influence the climate, and how the climate influences people and other parts of the Earth system.

A climate-literate person:

  • understands the essential principles of Earth’s climate system and the options to address human-caused climate change, which are summarized in this guide;
  • recognizes credible information about climate change and knows where to find it;
  • communicates about climate change in accurate and effective ways; and
  • is able to make informed decisions related to climate change.

Climate model A numerical representation of the climate system based on the physical, chemical, and biological properties of its components, their interactions, and feedback processes and accounting for some of its known properties. The climate system can be represented by models of varying complexity; that is, for any one component or combination of components, a spectrum or hierarchy of models can be identified, differing in such aspects as the number of spatial dimensions; the extent to which physical, chemical, or biological processes are explicitly represented; or the level at which empirical parameterizations are involved. Climate models are applied as a research tool to study and simulate long-term climate projections (decadal or longer) and operationally used to create shorter climate predictions (seasonal, annual, interannual).

Climate system The matter, energy, and processes involved in interactions among Earth’s atmosphere, hydrosphere, cryosphere, lithosphere, biosphere, and Earth-Sun interactions. (USGCRP, 2009)

Climate variability Deviations of climate variables from a given average state, including the occurrence of extremes, at all spatial and temporal scales beyond that of individual weather events. Variability may be intrinsic, due to fluctuations of processes internal to the climate system (i.e., internal variability), or extrinsic, due to variations in natural or anthropogenic external forcing (i.e., forced variability).

Coproduction (of knowledge) The integration of different knowledge systems and methodologies to systematically understand phenomena, systems, and processes.

Decent work Productive work for people in conditions of freedom, equity, security, and human dignity. (European Commission, 2022) (ILO, 2024)

Discrimination The differential treatment of an individual or group of people on the basis of, for example, their race, color, national origin, religion, sex (including pregnancy and gender identity), age, marital and parental status, disability, sexual orientation, or genetic information.

Drought An exceptional period of water shortage for existing ecosystems and the human population (due to low rainfall, high temperature and/or wind)

Earth system Earth functions as a system of interdependent parts. These parts include the physical, chemical, and biological processes that all interact to shape our planet and the organisms on it.

Eco-anxiety Also known as climate anxiety, a chronic fear of environmental doom.

Ecosystem A functional unit consisting of living organisms, their nonliving environment, and the interactions within and between them. The components included in a given ecosystem and its spatial boundaries depend on the purpose for which the ecosystem is defined. In some cases, ecosystem boundaries are relatively sharp, while in others they are diffuse, and they can change over time. Ecosystems are nested within other ecosystems, and their scale can range from very small to the entire biosphere. In the current era, most ecosystems either contain people as key organisms, or they are influenced by the effects of human activities in their environment. 

Emissions The release of climate-altering gases and aerosols into the atmosphere from human and natural sources.

Environmental injustice Environmental actions, behaviors, laws, and policies that have not been fair, that have limited meaningful involvement in environmental decision-making, or have unjustly allocated the risks and benefits of environmental action across communities, most often based on race, color, national origin, income, and gender identity, among others.

Equity The principle of being fair and impartial and a basis for understanding how the impacts and responses to climate change, including costs and benefits, are distributed in and by society in more or less equal ways. Often aligned with ideas of equality, fairness, and justice and applied with respect to equity in the responsibility for, and distribution of, climate impacts and policies across society, generations, and gender, and in the sense of who participates and controls the processes of decision-making.

Extreme events A weather event that is rare at a particular place and time of year, including, for example, heatwaves, cold waves, heavy rains, periods of drought and flooding, and severe storms. Definitions of “rare” vary, but an extreme weather event would normally be as rare as or rarer than the 10% or 90% probability density function estimated from observations. By definition, the characteristics of what is called extreme weather may vary from place to place in an absolute sense.

Extreme heat Temperatures that are much hotter and/or humid than average. Because some places are hotter than others, this depends on what is considered average for a particular location at that time of year.

Flooding The overflowing of the normal confines of a stream or other water body or the accumulation of water over areas that are not normally submerged.

Food web A diagram of the links among species in an ecosystem – essentially who eats what. A food chain shows only the organisms that contribute to the diet of the top consumer. (USGS, 2003)

Fossil fuels Carbon-based fuels from fossil hydrocarbon deposits, including coal, oil, and natural gas.

Global warming The increase in global surface temperature relative to a baseline reference period, averaging over a period sufficient to remove interannual variations (e.g., 20 or 30 years). A common choice for the baseline is 1850–1900 (the earliest period of reliable observations with sufficient geographic coverage), with more modern baselines used depending on the application.

Greenhouse effect The process through which heat is trapped near the Earth's surface by substances known as greenhouse gases. (NASA, 2024)

Greenhouse gas (GHG) Gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of radiation emitted by Earth’s surface, by the atmosphere itself, and by clouds. This property causes the greenhouse effect. Water vapor, carbon dioxide, nitrous oxide, methane, and ozone are the primary GHGs in Earth’s atmosphere. Other GHGs include sulfur hexafluoride, hydrofluorocarbons, chlorofluorocarbons, and perfluorocarbons; several of these are also ozone-depleting (and are regulated under the Montreal Protocol).

Hazard The potential occurrence of a natural or human-induced physical event or trend that may cause loss of life, injury, or other health impacts, as well as damage and loss to property, infrastructure, livelihoods, service provision, ecosystems, and environmental resources.

Heatwave A period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months. Heatwaves and warm spells have various and, in some cases, overlapping definitions.

High tide flooding Occurs when sea level rise combines with local factors to push water levels above the normal high tide mark. Changes in prevailing winds, shifts in ocean currents, and strong tidal forces (which occur during full or new moons) can all cause high tide flooding, inundating streets and other infrastructure even on sunny days.

Ice sheet An ice body originating on land that covers an area of continental size, generally defined as covering > 19,000 mi2 (>50,000 km2), and that has formed over thousands of years through accumulation and compaction of snow.

Impact (climate) The consequences of realized risks on natural and human systems, where risks result from the interactions of climate-related hazards (including extreme weather/climate events), exposure, and vulnerability. Impacts generally refer to effects on lives, livelihoods, health, and well-being; ecosystems and species; economic, social, and cultural assets; services (including ecosystem services); and infrastructure.

Indigenous Knowledges (IK); also, Traditional Knowledges/Traditional Ecological Knowledges (TEK) Bodies of dynamic and experiential knowledges gained over time by Indigenous Peoples, often associated with a specific place. IK includes observations, oral and written knowledge, innovations, practices, rituals, and beliefs; some IK is considered sacred and secret to a group or individuals. IK is inherently heterogeneous due to the cultural and geographic contexts from which it is derived. Also known as Native Science, Traditional Knowledges, Traditional Ecological Knowledges, or Indigenous Ways of Knowing.

Industrial era The multicentury period from the onset of large-scale industrial activity around 1750 to the present day. The reference period c. 1850–1900 is used to approximate preindustrial global average surface temperature. 

Inequity An unfair or unjust difference in the distribution, allocation, management, or use of a resource, benefit, or burden between groups of people.

Intergovernmental Panel on Climate Change Created in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), the objective of the Intergovernmental Panel on Climate Change (IPCC) is to provide governments at all levels with scientific information that they can use to develop climate policies. The IPCC provides regular assessments of the scientific basis of climate change, its impacts and future risks, and options for adaptation and mitigation. IPCC reports are also a key input into international climate change negotiations. (IPCC, 2024)

Just transition A set of principles, processes and practices that aim to ensure that no people, workers, places, sectors, countries, or regions are left behind in the transition from a high-carbon to a low-carbon economy. It stresses the need for targeted and proactive measures from governments, agencies, and authorities to ensure that any negative social, environmental, or economic impacts of economy-wide transitions are minimized, while benefits are maximized for those disproportionately affected. Key principles of just transitions include respect and dignity for vulnerable groups, fairness in energy access and use, social dialogue and democratic consultation with relevant stakeholders, the creation of decent jobs, social protection, and rights at work. Just transitions could include fairness in energy, land use, and climate planning and decision-making processes; economic diversification based on low-carbon investments; realistic training/retraining programs that lead to decent work; gender-specific policies that promote equitable outcomes; the fostering of international cooperation and coordinated multilateral actions; and the eradication of poverty. Lastly, just transitions may embody the redressing of past harms and perceived injustices.

Maladaptation (climate) Occurs when actions are taken that may lead to increased risk of adverse climate-related outcomes, including via increased greenhouse gas emissions, increased or shifted vulnerability to climate change, more inequitable outcomes, or diminished welfare, now or in the future. Most often, maladaptation is an unintended consequence.

Marginalized population/Marginalized community Community excluded from mainstream social, economic, educational, and/or cultural life. Examples of marginalized populations include, but are not limited to, groups excluded due to race, gender identity, sexual orientation, age, physical ability, language, and/or immigration status. 

Migration (human) Movement of a person or a group of persons either across an international border or within a nation. It is a population movement encompassing any kind of movement of people, whatever its length, composition, and causes; it includes migration of refugees, displaced persons, economic migrants, and persons moving for other purposes, including family reunification. 

Mitigation Measures to reduce the amount and rate of future climate change by reducing emissions of heat-trapping gases or removing carbon dioxide from the atmosphere.

National Climate Assessment (NCA) The U.S. Global Change Research Program (USGCRP) was established by Presidential initiative in 1989 and mandated by Congress in the Global Change Research Act (GCRA) of 1990. Its mandate is to develop and coordinate “a comprehensive and integrated United States research program which will assist the Nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change.” The GCRA mandates that USGCRP prepare and submit to the President and the Congress a quadrennial assessment, referred to as the National Climate Assessment (NCA). (USGCRP, 2023)

Natural climate solutions Actions to protect, sustainably manage, and restore natural or modified ecosystems for the purpose of climate change mitigation. (USAID, 2022)

Nature-based solutions 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.

Net-zero carbon dioxide emissions Condition in which anthropogenic carbon dioxide (CO2) emissions are balanced by anthropogenic CO2 removals over a specified period.

Ocean acidification The process by which the pH measurement of ocean water moves toward more acidic levels due to the absorption of carbon dioxide, which interacts with ocean water to form carbonic acid, thereby lowering the pH. Increased acidity reduces the ability of plankton and shelled animals to form and maintain carbonate-containing body parts such as shells.

Overburdened community Population or geographic location in the United States that experiences disproportionate environmental and climatic harms and risks. This disproportionality can be a result of greater vulnerability to environmental hazards, lack of opportunity for public participation, or other factors. Increased vulnerability may be attributable to an accumulation of negative or lack of positive environmental, health, economic, or social conditions within these populations or places. The term describes situations where multiple factors, including both environmental and socioeconomic stressors, may act cumulatively to affect health and the environment and contribute to persistent environmental health disparities.

Paris Agreement An international climate agreement adopted in 2015, which entered into force in 2016, with the central goal of holding the global average temperature rise to well below 2°C above preindustrial levels and pursuing efforts to limit the temperature increase even further to 1.5°C. Under this agreement, each party must, among other things, submit a “nationally determined contribution” (NDC)—that is, a greenhouse gas emissions target and/or mitigation policies and measures—every five years and regularly report on progress made in implementing and achieving its NDC. The agreement also addresses efforts to adapt to the adverse effects of climate change and certain support for developing country Parties, such as financial support for mitigation and adaptation.

Participatory processes Approaches to research and planning in which those most directly impacted by the outcomes become active participants in the process. (Adapted from National Academies of Sciences, Engineering, and Medicine, 2023)

Renewable energy Any form of energy that is replenished by natural processes at a rate that equals or exceeds its rate of use.

Resilience (climate) The capacity of interconnected social, economic, and ecological systems to cope with a climate change event, trend, or disturbance, responding or reorganizing in ways that maintain their essential function, identity, and structure. Climate resilience is a subset of resilience against climate-induced or climate-related impacts.

Risk Threats to life, health, and safety, the environment, economic well-being, and other things of value. Risks are evaluated in terms of how likely they are to occur (probability) and the damages that would result if they did happen (consequences).

Sea level rise Increase to the height of sea level, both globally and locally (relative sea level change) due to a change in ocean volume as a result of a change in the mass of water in the ocean (e.g., due to melt of glaciers and ice sheets), changes in ocean volume as a result of changes in ocean water density (e.g., expansion under warmer conditions), changes in the shape of the ocean basins, and changes in Earth’s gravitational and rotational fields, as well as local subsidence or uplift of the land. Sea level change refers to sea level rise or sea level fall.

Social systems The institutions, policies, programs, practices, values, and behaviors that shape drivers, risks, impacts, and understanding of climate change. (Adapted from USGCRP, 2023: Ch. 20)

Storm surge The temporary increase, at a particular locality, in the height of the sea due to extreme meteorological conditions (low atmospheric pressure and/or strong winds). The storm surge is defined as being the excess above the level expected from the tidal variation alone at that time and place.

Transformative adaptation Adaptation that changes the fundamental attributes of a social–ecological system, often involving persistent, novel, and significant changes to institutions, behaviors, values, and/or technology in anticipation of climate change and its impacts.

Tipping point The point at which a change in the climate triggers a significant environmental event, which may be permanent, such as widespread bleaching of corals or the melting of very large ice sheets.

Uncertainty (statistical) An expression of the degree to which a quantity or process is unknown. In statistics, a term used to describe the range of possible values around a best estimate, sometimes expressed in terms of probability or likelihood. Uncertainty about the future climate arises from the complexity of the climate system and the ability of models to represent it, as well as the inability to predict the decisions that society will make. There also is uncertainty about how climate change, in combination with other stressors, will affect people and natural systems.

Underserved community A community who, due to continuous systemic discrimination, under- or disinvestments, and limited access to efficient, healthy, and affordable services and infrastructure, experiences disproportionate environmental and climatic harms and risks and lack access to adequate resources to mitigate, respond to, and recover from impacts. Increased vulnerability may be attributable to harmful environmental, health, economic, or social conditions—or to a lack of support for positive conditions—within these populations or places. The term describes situations where disproportionate vulnerability is often due to discrimination based on geography; access to authority or representation in governance; or social identities, including race, ethnicity, gender, culture, economic status, or ability.

U.S. Global Change Research Program A federal interagency research program established by Congress in the Global Change Research Act of 1990. Its mandate is to develop and coordinate “a comprehensive and integrated United States research program which will assist the Nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change.” (USGCRP, 2024)

United Nations Framework Convention on Climate Change (UNFCCC) An international climate agreement adopted in 1992, which entered into force in 1994. The objective of the UNFCCC is to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.

Vector (disease) An organism, such as an insect, that transmits disease-causing microorganisms such as viruses or bacteria. Vector-borne diseases include, for example, malaria, Lyme disease, Zika, and chikungunya.

Vulnerability (climate) The degree to which physical, biological, and socioeconomic systems are susceptible to and unable to cope with adverse impacts of climate change.

Weather The state of the atmosphere, mainly with respect to its effects on life and human activities. As distinguished from climate, weather consists of short-term (minutes to days) variations in the atmosphere. Popularly, weather is thought of in terms of temperature, humidity, precipitation, cloudiness, visibility, and wind.

Well-being (human) A state of existence that fulfills various human needs, including material living conditions and quality of life, as well as the ability to pursue one’s goals, to thrive, and to feel satisfied with one’s life.

Wildfire A wildland fire originating from an unplanned ignition, such as lightning, volcanos, unauthorized and accidental human-caused fires, and prescribed fires that are declared wildfires.

Literature Cited