Glossary
Afforestation Planting of new forests on lands that historically have not contained
forests
Agenda 21 A document accepted by the participating nations at UNCED on a
wide rangeof environmental and developmentissues for the twenty-first
century
Albedo The fraction of light reflected by a surface, often expressed as a
percentage. Snow-covered surfaces have a high albedo level;
vegetation-covered surfaces have a low albedo, because of the light absorbed
forphotosynthesis
Anthropic principle A principle which relates the existence of the Universe to
the existence of humans who can observe it
Anthropogenic effects Effects which result from human activities such as the
burning offossil fuelsordeforestation
AOGCM Atmosphere–Ocean CoupledGeneral Circulation Model
Atmosphere The envelope of gases surrounding the Earth or other planets
Atmospheric pressure The pressure of atmospheric gases on the surface of the
planet. High atmospheric pressure generally leads to stable weather
conditions, whereas low atmospheric pressure leads to storms such as
cyclones
Atom The smallest unit of anelementthat can take part in a chemical reaction.
Composed of a nucleus which containsprotonsandneutronsand is surrounded
byelectrons
Atomic mass The sum of the numbers ofprotonsandneutronsin the nucleus of
anatom
Biodiversity A measure of the number of different biological species found in a
particular area
Biological pump The process whereby carbon dioxide in theatmosphereis
dissolved in sea water where it is used forphotosynthesisbyphytoplankton
which are eaten byzooplankton. The remains of these microscopic organisms
sink to the ocean bed, thus removing the carbon from thecarbon cyclefor
hundreds, thousands or millions of years
Biomass The total weight of living material in a given area
Biome A distinctive ecological system, characterised primarily by the nature of its
vegetation
Biosphere The region on land, in the oceans and in theatmosphereinhabited by
living organisms
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