California Climate Change Glossary

Letter A

Absorption lines. Any portion of the electromagnetic spectrum (including visible light) that is trapped by free atoms or molecules in the path of the radiation, thus reducing their transmission. In the climate context, this is important for the greenhouse effect since water vapor, carbon dioxide and methane absorb certain wavelengths of infrared radiation. (Calspace)

Absorption of Radiation. The uptake of radiation by a solid body, liquid or gas. The absorbed energy may be transferred or re-emitted. (EPA)

Acid Rain. Also known as "acid deposition." Acidic aerosols in the atmosphere are removed from the atmosphere by wet deposition (rain, snow, fog) or dry deposition (particles sticking to vegetation). Acidic aerosols are present in the atmosphere primarily due to discharges of gaseous sulfur oxides (sulfur dioxide) and nitrogen oxides from both anthropogenic and natural sources. In the atmosphere these gases combine with water to form acids. (EPA)

Adaptive Capacity. The ability of a system (like an ecosystem) to adapt to climate change or other environmental disturbances. This may mean moderating potential damages, taking advantage of opportunities or coping with the consequences. In discussions on global warming adaptive capacity often refers to a country. In this case it is currently much lower in developing countries, consequential to poverty. (Lenn)

Adiabatic expansion/compression. Expansion (or compression) of a gas (e.g. air) without exchange of heat with the surroundings. Air cools upon expansion and heats up upon compression, and this is the main reason for the vertical temperature gradient seen in the lower atmosphere (i.e. the troposphere). The adiabatic temperature gradient in dry air is near 1°C for every 100 m change in elevation. The actual gradient on Earth is less because of the presence of water in the air. (Calspace)

Aerosols. Particles of matter, solid or liquid, larger than a molecule but small enough to remain suspended in the atmosphere. Natural sources include salt particles from sea spray and clay particles as a result of weathering of rocks, both of which are carried upward by the wind. Aerosols can also originate as a result of human activities and in this case are often considered pollutants. See also Sulfate Aerosols. (EPA)

Afforestation. The Revised 1996 Intergovernmental Panel on Climate Change (IPCC) Inventory Guidelines defines afforestation as the planting of new forests on land which historically been covered by forest. (Australia)

Agassiz, Jean Louis Rudolphe (1807-1877). Swiss naturalist, paleontologist and geologist. He received his degree in medical sciences 1830 and followed by studying with Cuvier at the Musée d'Histoire Naturelle in Paris (1831-32). In 1832 he became a professor in Neuchâtel, and then in 1848 he served as professor at Harvard, where he founded the Museum of Comparative Zoology in 1858. A world expert on fishes, mollusks and echinoderms, Agassiz was also the originator of the concept of the "Great Ice Age," an idea which proved to be useful for the investigation of climate change and for the reconstruction of ice age history. He was the last distinguished paleontologist to reject Darwin's evolutionary theories in favor the ideas of repeated extinction and creation events, in the tradition of d'Orbigny and Cuvier. (Calspace)

Albedo. The ratio of reflected to incident light; albedo can be expressed as either a percentage or a fraction of 1. Snow covered areas have a high albedo (up to about 0.9 or 90%) due to their white color, while vegetation has a low albedo (generally about 0.1 or 10%) due to the dark color and light absorbed for photosynthesis. Clouds have an intermediate albedo and are the most important contributor to the Earth's albedo. The Earth's aggregate albedo is approximately 0.3. (EPA)

Alleroed. A village in Denmark whose name is used for a warm period at the end of the last glacial. (Calspace)

Alliance of Small Island States (AOSIS). The group of Pacific and Caribbean nations who call for relatively fast action by developed nations to reduce greenhouse gas emissions. The AOSIS countries fear the effects of rising sea levels and increased storm activity predicted to accompany global warming. Its plan is to hold Annex I Parties to a 20 percent reduction in carbon dioxide emissions by the year 2005. (EPA)

Allometric Equation. An equation that uses know growth measurements to estimate related unknown growth measurements (e.g. using tree trunk girth measurements to estimate root biomass). (Australia)

Altimitry. A state-of-the-art radar technique that measures global elevation of sea, land, or ice surfaces compared to the center of the earth. (Lenn)

Annex I Parties. Industrialized countries that, as parties to the Framework Convention on Climate Change, have pledged to reduce their greenhouse gas emissions by the year 2000 to 1990 levels. Annex I Parties consist of countries belonging to the Organization for Economic Cooperation and Development (OECD) and countries designated as Economies-in-Transition. (EPA)

Anthropogenic. Derived from human activities. (EPA)

Anthropogenic Emissions. Emissions of particles or substances resulting from human activities, such as industry and agriculture. (Lenn)

Arrhenius, Gustaf (born 1922). Swedish-American geochemist and a member of the Swedish Deep-Sea Expedition (1947-1949). He discovered cyclic sedimentation in the long cores taken in the equatorial Pacific and related these observations to climate cycles in the ice ages. He is currently a professor at the Scripps Institution of Oceanography at UC San Diego. (Calspace)

Arrhenius, Svante (1859-1927). Swedish physicist and chemist who discovered ionic dissociation and its role in making solutions conduct an electric current. He predicted global warming from the release of carbon dioxide to the atmosphere and made calculations on the magnitude of the effect. (Calspace)

Atlantic Heat Conveyor. The considerable heat transfer from south to north by near-surface waters moving across the equator in the Atlantic. This movement is required to balance a southward flow of water in the ocean depths. This deep water, called the "North Atlantic Deep Water," moves sluggishly but the flow is considerable - some 20 Sverdrup - and is rather cold (between about 2°C and 4°C). So since the North Atlantic trades cold water for warm, it gains lots of heat in the process. This is the reason regions well north of 60°N, such as in Scandinavia, have comparably mild climates. The graph below shows the flow of heat (in units of 1013 Watts) across the present Atlantic ("+" symbol), across the Atlantic during glacial times ("o" symbol), and the world ocean average (thick solid line bordered by thin lines that represent the upper and lower limits ). The general trend to take from the graph is that heat is transported from southern to northern latitudes. (Calspace)

Atmosphere. Definition 1: The mixture of gases surrounding the Earth. The Earth's atmosphere consists of about 79.1% nitrogen (by volume), 20.9% oxygen, 0.036% carbon dioxide and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally determined by its thermal properties (temperature). The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 km (about 5 miles) in the polar regions and up to 17 km (nearly 11 miles) above the equator. The stratosphere, which reaches to an altitude of about 50km (31 miles) lies atop the troposphere. The mesosphere which extends up to 80-90 km is atop the stratosphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers. (EPA)

Definition 2: A blanket of air surrounding the earth that supports life. The atmosphere absorbs energy from the sun, recycles water and other chemicals and works with electrical and magnetic forces to provide a moderate climate. It also protects us from high-energy radiation and the frigid vacuum of space.

The atmosphere is primarily composed of nitrogen (79%), oxygen (21%), and argon (1%). Other components include water (0-7%), ozone (0-0.01%) and carbon dioxide (0.01-0.1%).

The atmosphere changes from the ground up and consists of four distinct layers: troposphere (8-14.5 km), stratosphere (14.5-50 km), mesosphere (50-85 km) and thermosphere (85-600 km). Temperatures are different for each layer. In the troposphere temperatures drop from about 17 to -52 degrees Celcius, in the stratosphere temperatures increase gradually to -3 degrees Celcius, in the mesosphere temperatures fall to -93 degrees Celcius as altitude increases, and in the thermosphere temperatures can be as high as 1,727 degrees Celsius when objects are in direct sunlight. (See figure on the right.)

Above the thermosphere, the exosphere starts and continues until it mixes with interplanetary gases or space. This layer primarily consists of very low-density particles such as hydrogen and helium. (Lenn)

Attribution of climate change. The process of establishing the most likely causes for the detected climate change with some defined level of confidence. (Lenn)

Axelrod, Daniel I. (1910-1998). American paleoecologist who who reconstructed past climates, vegetation types, and entire landscapes from fossil impressions of leaves, stems, cones, and fruits. (Calspace)