Climate change refers to significant changes in global temperature, precipitation, wind patterns and other measures of climate that occur over several decades or longer.

The seas are rising. The foods we eat and take for granted are threatened. Ocean acidification is increasing. Ecosystems are changing, and for some, that could spell the end of certain regions the way we have known them. And while some species are adapting, for others, it’s not that easy.

Evidence suggests many of these extreme climate changes are connected to rising levels of carbon dioxide and other greenhouse gases in the Earth’s atmosphere — more often than not, the result of human activities.

Search below for key terms and definitions related to climate change.


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).

Antarctic sea ice

Antarctic sea ice is nearly a geographic opposite of its Arctic counterpart because Antarctica is a landmass covered in ice surrounded by an ocean, and the Arctic is an ocean of sea ice surrounded by land.


Anthropogenic describes 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.

Arctic sea ice

Arctic sea ice is an integral part of the Arctic Ocean and an important indicator of climate change. During winter’s dark months, sea ice will typically cover the majority of the Arctic Ocean.


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 atmospheric carbon dioxide.

Climate change adaptation

Climate change adaptation refers to the adjustments societies or ecosystems make to limit the negative effects of climate change or to take advantage of opportunities provided by a changing climate. Adaptation can range from farmers planting more drought-resistant crops to coastal communities evaluating how best to protect themselves from sea level.

Climate forcing

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

Climate science

Climate science studies how changing climates affect the natural order on a global level. Rising global temperatures bring with them the potential to raise sea levels to raise sea levels, change precipitation and local climate conditions.

Coastal Wetlands

Coastal wetlands include saltwater and freshwater wetlands located within coastal watersheds — specifically USGS 8-digit hydrologic unit watersheds which drain into the Atlantic Ocean, Pacific Ocean, or Gulf of Mexico.


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.


Emissions are substances released into the air and are measured by their concentrations, or parts per million, in the atmosphere.


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


Glaciers and ice caps form on land. Glaciers accumulate snow, which over time becomes compressed into ice. On average, glaciers worldwide have been losing mass since at least the 1970s.

Global temperature

Global temperature is an average of air temperature recordings from weather stations on land and sea as well as some satellite measurements. Worldwide, 2006-2015 was the warmest decade on record since thermometer-based observations began nearly 150 years ago.

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. The next most plentiful 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.

Heat domes

A heat dome is when hot ocean air gets trapped over a large area, resulting in dangerously high temperatures. It occurs when high atmospheric pressure forms over a region, pushing air down, which heats as the air compresses. This forms a “lid” that seals to create a dome of trapped heat, setting the stage for heat waves.

Hydrologic cycle

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

Hydrologic model

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

Ice Loss

Ice loss refers to the retreat of sea ice and land ice mass from its historic extents. This retreat of sea ice and land ice is one of two major causes of the current sea level rise.

Ice Sheet

An ice sheet forms on land and extends over tens of thousands of miles. Greenland and Antarctica have vast ice sheets that together contain more than 99 percent of the freshwater ice on Earth. In Greenland, today’s record summer melts bring rapid and widespread ice sheet loss. In Antarctica, the melt is slower and more localized for now.

Ice Shelf

An ice shelf forms from the outflow of land ice and floats on the sea at the land’s edge. It creates a barrier that slows the flow of land ice into the ocean. In the last thirty years, both rapid disintegration of ice shelves and ice shelf collapses have been observed along Canada and the Antarctic Peninsula.


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.


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


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 important in discussions about power plants and 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. 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 and more common items. 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. It acts as a barrier to global warming. Specifically, the ozone layer keeps 95-99% of the sun’s ultraviolet radiation from striking the Earth.

Ozone forming potential

Ozone forming potential is a measure of the reactivity of an individual chemical compound to the presence of other chemicals that form ozone together.

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.

Polar Vortex

The polar vortex is a large area of low pressure and cold air around Earth’s North Pole. The phenomenom typically goes unnoticed by those of us living in lower latitudes except for when, every once in a while, the air pressure and winds shift.

Primary production

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

Renewable energy

Renewable energy is energy from sources that will renew themselves within our lifetime. Renewable energy sources include wind, sun, water, biomass (vegetation) and geothermal heat.

Sea ice

Sea ice, both Antarctic and Arctic seas, forms from salty ocean water. Overall, the Earth has lost a mass of sea ice the size of Maryland each year since 1979.

Sea level

Sea level is the average level between high tide and low tide where the surface of the sea meets a shoreline.

Sea level rise

Sea level rise describes an increase in the average level between high tide and low tide where the surface of the sea meets a shoreline.

Seed particles

Seed particles are tiny solid or liquid particles that provide a non-gaseous surface. The surface allows 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 period 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.

Solar Power

Solar power refers to the energy harnessed from the sun, which can then be transformed into different types of energy, including thermal and electric.


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. This type of light 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 one percent of the atmosphere. Most of the atmosphere is made up of nitrogen (78 percent by volume) and oxygen (21 percent by volume).


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

Transportation Control Measures

Transportation Control Measures describe travel demand management measures to help reduce 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.


Wildfires are unplanned burns in any natural environment, like a forest or a grassland. Wildfire can spread quickly, burning through most anything in their path, causing injury and death to people and animals.

Experts Answer 8 Important Wildfire Questions

5 Ways to Prevent and Prepare for Wildfires

Wildland-urban interface

The wildland-urban interface is where the wilderness meets a well-populated area. A wildfire that crosses this divide becomes more dangerous because there is a higher chance of burning people’s homes and releasing toxic materials that can cause significant harm to humans and animals. It can also directly lead to more deaths. According to UC Davis researchers, wildfires are crossing the wildland-urban interface more frequently.