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Climate Change

Science Supporting Policy in California and Beyond

Photo: Dale Uyeminami, UC Davis Staff Research Associate

UC Davis Staff Research Associate Dale Uyeminami is on the team that analyzes the products of combustion to better understand air pollution. This research is part of the San Joaquin Valley Aerosol Health Effects Center at UC Davis founded in 2005 by an $8M EPA Grant. (Sylvia Wright/UC Davis)  » READ MORE

Terms and Definitions

Aerosol refers to small suspended particles in a gas. They range in size from one nanometer (one billionth of a meter) to 100 micrometers (one millionth of a meter).

Anthropogenic is generated by human beings.

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

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

Biogenic emissions are emissions generated by living things.

Biological productivity is the amount of plants and animals that grow and thrive in a defined region.

Carbon is an elemental building block of molecules that make up all organisms on Earth. In a forest, carbon is stored in plant tissues (through photosynthesis) and is emitted back into the atmosphere through respiration.

Carbon cycling is the process by which living things absorb carbon from the atmosphere, or carbonate rocks and ocean deposits (limestone and coral), or dead organic matter in the soil, or food; after which carbon is returned to the atmosphere by respiration, combustion, or decay, in the form of carbon dioxide or methane.

Carbon dioxide represents 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), therefore as energy use increases, so do carbon dioxide emissions.

Carbon sequestration is the process of removing carbon from the atmosphere and storing it in a carbon sink, a fixed molecule in soil, oceans or plants. Because of the amounts of carbon that are stored in soils, small changes in soil carbon content can have major impacts on carbon dioxide levels in the atmosphere. 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.

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 are the benefits or "services" of the ecosystem to human life, such as clean water and the natural decomposition of waste.

Electrolytes are substances containing free ions that conduct electricity.

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

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. Since 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) of a greenhouse gas is based on its ability 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. However, its GWP over 100 years increases to 22,200.

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 remaining gases are anthropogenic, meaning they can be attributed to human activity. These are increasing faster than they are removed from the atmosphere.

Ground level ozone is the main component of smog and is a product of reactions among chemicals produced by burning coal, gasoline and other fuels called nitrous oxides or Nox, and chemicals called Volatile Organic Compounds found in solvents, paints, hairsprays, etc. Ozone consists of three oxygen atoms.

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

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 outcomes.

Methane 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. Coal mining was a significant source of methane, however emissions from about 7500 abandoned mines are variable and unaccounted for. Methane emissions from vehicles have decreased through the use of catalytic converters.

Mesoscale ranges from a few to a few hundred miles. It includes local winds, thunderstorms, and tornadoes.

A micron, also called a micrometer, is one millionth of a meter, or a thousandth of a millimeter. Because of their size (approximately 1/30th the average width of a human hair), particles at 2.5 microns lodge deeply into the lungs.

Mitigation potential is the amount of carbon that can be stored in order to balance the release of carbon from other sources, such as power plants or vehicles.

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

Nitrous oxide is the main regulator of stratospheric ozone and one of six gases addressed by the Kyoto Protocol. Crops and livestock were the source of 76 percent of U.S. nitrous oxide emissions in 2005. Nitrogen fertilization of soil and animal waste are the largest contributors. Although nitrous oxide made up only five percent of the total US greenhouse gas emissions in 2005, it has nearly 300 times the global warming potential of carbon dioxide over 100 years.

Ninety percent of ozone resides in a layer from six to 25 miles above the Earth's surface called the stratosphere. Ozone depletion is a concern because the ozone layer keeps 95-99% of the suns ultraviolet radiation from striking the earth.

Ozone forming potential is the reactivity of an individual compound to the presence of other precursors and factors for the formation of ozone.

Particulate matter (PM-10) is a type of air pollution that includes 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. It causes eye, nose and throat irritation and respiratory problems.

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

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 is obtained from taking a vertical core of the lake bottom sediment and analyzing the layers.

Sensitivity analysis is the study of how the variation in the output of a model can be attributed to different sources of variation.

Soil organic carbon (SOC) can be either a source or a sink for atmospheric carbon dioxide and is thus an important reservoir in the global carbon cycle.

The solar cycle is the eleven-year cycle of the solar activity of the sun, first determined in 1843 by German astronomer Heinrich Schwabe. Solar variations in output have been measured from satellites. Climate scientists are trying to determine how much the variations effect the temperature of Earth's atmosphere.

Stratosphere is a layer of the atmosphere 9-31 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 a large-scale weather system more than 200 miles across.

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

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 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 are travel demand management measures for the purpose of reducing emissions or concentrations of air pollutants from transportation sources by reducing vehicle use or changing traffic flow or congestion conditions.

Volatile organic compounds, or volatile organic carbon, are emitted as gases from solids or liquids. VOCs are emitted by thousands of manmade 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 is the full depth of a lake from the surface to the bottom.