Aerosols - microscopic particles originating from both natural sources (e.g., volcanoes) and human activities (e.g., coal burning).

Afforestation – planting of new forests on lands not recently forested.

Albedo - the reflectivity of Earth. Unreflected light is converted to infrared radiation (i.e., heat), which causes atmospheric warming.

Alternative energy - energy derived from nontraditional sources (e.g., compressed natural gas, solar, hydroelectric, wind).

Biofuel - gas or liquid fuel made from plant material (biomass). Includes wood, wood waste,wood liquors, peat, railroad ties,wood sludge, spent sulfite liquors, agricultural waste, straw, tires, fish oils, tall oil, sludge waste, waste alcohol, municipal solid waste, landfill gases and ethanol blended into motor gasoline.

Biomass - technically, the total dry organic matter or stored energy content of living organisms in a given area. Biomass refers to forms of living matter (e.g., grasses, trees) or their derivatives (e.g., ethanol, timber, charcoal) that can be used as fuels.

Biomass energy - energy produced by combusting biomass materials such as wood. The carbon dioxide emitted from burning biomass will not increase total atmospheric carbon dioxide if this consumption is done on a sustainable basis (i.e., if in a given period of time, regrowth of biomass takes up as much carbon dioxide as is released from biomass combustion). Biomass energy is often suggested as a replacement for fossil fuel combustion.

Capital Stock - existing investments in energy plant and equipment that may or may not be modified once installed.

Carbon cycle - general term used in reference to the sum of all reservoirs and flows of carbon on Earth. The flows tend to be cyclic in nature; for example, carbon removed from the atmosphere (one reservoir) and converted into plant tissue (another reservoir) is returned back into the atmosphere when the plant is burned.

Carbon reservoir or sink - within the carbon cycle, the physical site at which carbon is stored (e.g., atmosphere, oceans, Earth’s vegetation and soils, and fossil fuel deposits).

Carbon sequestration - The uptake and storage of carbon. Trees and plants absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned.

Certified Emissions Reduction (CER) - reductions of greenhouse gases achieved by a Clean Development Mechanism (CDM) project. A CER can be sold or counted toward Annex I countries’ emissions commitments. Reductions must be additional to any that would otherwise occur.

Climate - the average weather together with its variability of representations of the weather conditions for a specified area during a specified time interval (usually decades).

Climate Change - changes in long-term trends in the average climate, such as changes in average temperatures. In IPCC usage, climate change refers to any change in climate over time, whether due to natural variability or as a result of human activity. In UNFCC usage, climate change refers to a change in climate that is attributable directly or indirectly to human activity that alters atmospheric composition.

Deforestation - converting forest land to other vegetation or uses (e.g., cropland, pasture, dams).

Emissions - flows of gases, liquid droplets or solid particles into the atmosphere. Gross emissions from a specific source are the total quantity released. Net emissions are gross emissions minus flows back to the original source. Plants, for example, take carbon from the atmosphere and store it as biomass during photosynthesis, and they release it during respiration, when they decompose, or when they are burned.

Forest - terrestrial ecosystem (biome) with enough average annual precipitation (at least 76 centimeters or 30 inches) to support growth of various species of trees and smaller forms of vegetation.

Fossil fuel - coal, petroleum, or natural gas or any fuel derived from them.

Global warming - the apparent recent trend of increasing world-surface and tropospheric temperatures, thought to be caused by pollutants, and their “entrapment” of heat. This phenomenon is known as “the greenhouse effect.”

Greenhouse effect - the effect produced as certain atmospheric gases allow incoming solar radiation to pass through to Earth’s surface, but prevent the outgoing (infrared) radiation, which is re-radiated from Earth, from escaping into outer space. The effect is responsible for warming the planet.

Greenhouse gas - any gas that absorbs infrared radiation in the atmosphere.

Hydrocarbon - a large class of organic chemicals made up of carbon atoms linked to hydrogen and, sometimes, oxygen. Hydrocarbons are used for fuel and other economically important materials. Hydrocarbons can be altered by the addition of other chemicals, such as halogens.

Ozone - a molecule consisting of three bound atoms of oxygen. Its chemical nomenclature is O3. Most oxygen in the atmosphere, O2 , consists of only two oxygen atoms.

Ozone layer - ozone does not occur in a flat “layer” in the atmosphere. This term refers to ozone in the stratosphere where it occurs in its highest concentrations - roughly from 1 to 10 parts per million. This atmospheric zone lies between 15 and 50 kilometres above Earth’s surface, depending upon latitude, season, and other factors.

Radiation - refers to electromagnetic energy, not to be confused with “radioactivity” (the emission of radiation, generally alpha or beta particles from the nucleus of an unstable isotope).

Sequestration - an pportunity to remove atmospheric CO2, either through biological processes (e.g. plants and trees), or geological processes through storage of CO2 in underground reservoirs.

Sinks - any process, activity or mechanism that results in the net removal of greenhouse gases, aerosols, or precursors of greenhouse gases from the atmosphere.

Source - any process or activity resulting in the net release of greenhouse gases, aerosols, or precursors of greenhouse gases into the atmosphere.

Stratosphere - the Earth’s atmosphere 10-50 km above the surface of the planet.

Subsidiary Body for Scientific & Tech. Advice (SBSTA) - a permanent body established by the UNFCCC that serves as a link between expert information sources such as the IPCC and the COP.

Substitution - the economic process of trading off inputs and consumption due to changes in prices arising from a constraint on greenhouse gas emissions.

Targets and Timetables - the percent reduction from the 1990 emissions baseline that the country has agreed to. On average, developed countries agreed to reduce emissions by 5.2% below 1990 emissions during the period 2008-2012, the first commitment period.

Thermohaline Circulation (THC) - a three-dimensional pattern of ocean circulation driven by wind, heat and salinity that is an important component of the ocean-atmosphere climate system.

Trace Gas – gases found in the Earth’s atmosphere other than nitrogen, oxygen, argon and water vapor. Carbon dioxide, methane, and nitrous oxide are classified as trace gases.

Troposphere - the Earth’s atmosphere 0-10 km above the planet’s surface.

UN Framework Convention on Climate Change - a treaty signed at the 1992 Earth Summit in Rio de Janeiro. It calls for the “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” It took effect in March 1994 upon ratification by more than 50 countries.

Uncertainty - a prominent feature of the benefits and costs of climate change. Decision-makers compare risk of premature or unnecessary actions with risk of failing to take actions that subsequently prove to be earnt.

Vector-borne disease result from an infection transmitted to humans and other animals by blood-feeding anthropods, such as mosquitoes, ticks, and fleas. Examples include Dengue fever, viral encephalitis and malaria.

Water Vapor - the primary gas responsible for the greenhouse effect. It is believed that increases in temperature caused by anthropogenic emissions of greenhouse gases will increase the amount of water vapor in the atmosphere, resulting in additional warming.

Weather - the short-term (i.e., hourly and daily) state of the atmosphere. Weather is not the same as climate.