Climate Change Terms and Definitions


Aerosols are small suspended particles in a gas. Scientists can detect them in the atmosphere. They range in size from one nanometer (one billionth of a meter) to 100 micrometers (one millionth of a meter).


Anthropogenic is used to describe a process or result generated by human beings.


Aquaculture uses a body of water for the cultivation of plants and animals. (Compare to agriculture, which uses land to cultivate plants and animals.) Ponds, lakes, rivers, and the ocean serve as places to breed, rear and harvest aquatic species.


Aquifer is water-bearing rock from which water can be pumped.


Biofuels are renewable fuels derived from biological materials, such as algae and plants, that can be regenerated. This distinguishes them from fossil fuels, which are considered nonrenewable. Example of biofuels are ethanol, methanol and biodiesel.

Biogenic emissions

Biogenic emissions are emissions generated by living things.

Biological productivity

Biological productivity is a measure of the amount of plant and animal growth in a defined region and time.


Carbon is a configuration of molecules and an elemental building block of all organisms on Earth.

Carbon cycle

Carbon cycle describes the process by which living things absorb carbon from the atmosphere, sediments and soil, or food. To complete the cycle, carbon returns to the atmosphere in the form of carbon dioxide or methane by respiration, combustion or decay.

Carbon dioxide

Carbon dioxide is the gas that accounts for about 84 percent of total U.S. greenhouse gas emissions. In the U.S. the largest source of carbon dioxide (98 percent) emissions is combustion of fossil fuels. Combustion can be from mobile (vehicles) or stationary sources (power plants). As energy use increases, so do carbon dioxide emissions.

Carbon Sequestration

Carbon sequestration is the process of removing carbon from the atmosphere and storing it in a fixed molecule in soil, oceans or plants. An organism or landscape that stores carbon is called a carbon sink. An organism or landscape that emits carbon is called a carbon source. For example, soils contain inorganic carbon (calcium carbonate) and organic carbon (humus) and can be either a source or a sink for atmospheric carbon dioxide, depending on how landscapes are managed. Because large amounts of carbon are stored in soils, small changes to soil can have major impacts on carbon dioxide levels in the atmosphere.

Climate forcing

Climate forcing refers to how climate affects the physical, chemical and biological attributes of a region.


Dimethylsulfide is the most abundant biological sulfur compound emitted to the atmosphere, mostly from phytoplankton, and encourages cloud formation.

Ecosystem services

Ecosystem services are the benefits or “services” of an ecosystem to human life, such as clean water and the decomposition of organic matter.


Electrolytes are chemical substances containing free ions that conduct electricity.


Feedstock is raw material, usually plant or agricultural waste, that can be processed into fuel or energy.

Global warming

In the early 1960s scientists recognized that carbon dioxide in the atmosphere was increasing. Later they discovered that methane, nitrous oxide and other gases were rising. Because these gases trap heat and warm the Earth, as a greenhouse traps heat from the sun, scientists concluded that increasing levels of “greenhouse gases” would increase global warming.

Global Warming Potential (GWP)

Global Warming Potential (GWP) is the ability of a greenhouse gas to absorb heat compared to carbon dioxide over a specified period of time, from 20 to 500 years. The timeframe is important because each gas has a different rate at which it is removed from the atmosphere. For each time period, carbon dioxide is always set at “1”, and other greenhouse gases are compared to carbon dioxide for the same timeframe. For example, the sulfur hexafluoride’s GWP at 20 years is 15,100, meaning it has 15,100 times more warming potential than carbon dioxide in that timeframe.

Greenhouse gases

The main greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Water vapor is the most plentiful at about one percent, and the next is carbon dioxide at 0.04 percent. The effect of human activity on global water vapor concentrations is too small to be important. The effects of human activity on the other greenhouse gases, however, is large and very important. These gases are increasing faster than they are removed from the atmosphere.

Hydrologic cycle

Hydrologic cycle is the process by which water moves around the earth, and includes evaporation, precipitation, runoff, condensation, transpiration, and infiltration.

Hydrologic model

Hydrologic model is a computer analysis of large amounts of historical data to predict how variables such as temperature, rain, and carbon dioxide levels might affect the hydrologic cycle.


Methane is a gas and represents about 8 percent of total U.S. greenhouse gas emissions. The largest sources are wood burning in stoves and fireplaces, livestock digestive systems, and decomposition in landfills. Methane emissions from vehicles have decreased through the use of catalytic converters.


Mesoscale is a measure of distance useful for local winds, thunderstorms and tornadoes. It ranges from a few to a few hundred miles.


A micron, also called a micrometer, is one millionth of a meter, or a thousandth of a millimeter. It is a common measure for particulate matter in the atmosphere. Particles measuring only 2.5 microns (approximately 1/30th the average width of a human hair) lodge deeply into the lungs.

Mitigation potential

Mitigation potential is a measurement of the amount of carbon that can be stored in order to balance the release of carbon. It is often used in discussed about power plants or vehicles.


Nano refers to nanometer, one billionth of a meter or a hundred-thousandth of a millimeter.

Nitrous oxide

Nitrous oxide is one of six gases addressed by the Kyoto Protocol international agreement and the main regulator of stratospheric ozone. Animal waste and nitrogen fertilization of soil are the largest contributors. Although nitrous oxide made up only five percent of the total U.S. greenhouse gas emissions in 2005, these nitrogen emissions have nearly 300 times the global warming potential of carbon dioxide over 100 years.

Ocean Acidification

Ocean Acidification is the change in ocean chemistry due to decreasing pH levels, or increasing acidity, in seawater.


Ground level ozone is a gas produced through reactions between nitrous oxides (NOX) and volatile organic compounds (VOCs) when burning coal, gasoline and other fuels. VOCs are found in solvents, paints, hairsprays, etc. Ozone consists of three oxygen atoms and is the main component of smog.

Stratospheric ozone is a gas found in a layer from six to 25 miles above the Earth’s surface. Ozone depletion is a concern because the ozone layer keeps 95-99% of the sun’s ultraviolet radiation from striking the Earth, therefore acting as a barrier to global warming.

Ozone forming potential

Ozone forming potential is a measure of the reactivity of an individual chemical compound to the presence of other precursor chemicals and factors for the formation of ozone.

Particulate matter

Particulate matter (PM-10) are aerosols including dust, soot and tiny bits of solid materials that are released and move around in the air. Sources are burning of diesel fuels, incineration of garbage, mixing and applying fertilizers and pesticides, road construction, steel making, mining, field burning, forest fires, fireplaces and woodstoves. PM causes eye, nose and throat irritation and respiratory problems.

Primary production

Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis.

Seed particles

Seed particles are tiny solid or liquid particles that provide a non-gaseous surface to allow water to make the transition from a vapor to a liquid.

Sediment data

Sediment data are materials and measurements obtained from taking a vertical core of lake bottom sediment and analyzing the layers.

Sensitivity analysis

Sensitivity analysis is an interpretation of different sources of variation in the output of a predictive model.

Solar Cycle

The solar cycle describes the sun’s activity over its eleven-year periods of movement and related variations. The cycle was first determined in 1843 by German astronomer Heinrich Schwabe. Scientists are trying to determine how much solar variations affect the temperature of Earth’s atmosphere.


Stratosphere is a layer of the atmosphere nine to 31 miles above the Earth. Ozone in the stratosphere filters out harmful sun rays, including a type of sunlight called ultraviolet B, which causes health and environmental damage.


Synoptic is used to describe a large-scale weather system more than 200 miles across.

Thermochemical technologies

Thermochemical technologies are methods of capturing the energy potential of biomass.

Thermodynamic modules

Thermodynamic modules are the portions of models that predict changes in aerosols due to temperature.


Tillage refers to cultivation of the soil to improve production of crops.

Trace gases

Trace gases make up only 1% of the atmosphere. Most of the atmosphere is made up of nitrogen (78% by volume) and oxygen (21% by volume).


Transpiration is the evaporation of water into the atmosphere from the leaves and stems of plants and accounts for approximately 90% of all evaporating water.

Transportation Control Measures

Transportation Control Measures describe travel demand management measures to help reduce emissions or concentrations of air pollutants from transportation sources.

Volatile organic compounds

Volatile organic compounds, or volatile organic carbon, are chemical compounds from solids or liquids that are emitted as gases. VOCs are emitted by thousands of man-made sources including paints, lacquers, cleaning supplies, pesticides, building materials, furnishings, copiers, correction fluids, adhesives, permanent markers, cleaners and disinfectants, fuels, crude oil and cosmetics. Natural sources are trees, termites, cows (ruminants) and agricultural cultivation.

Water column

Water column is the full depth of a lake from the surface to the bottom.

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