Term name Description
AbioticNon-living (cf. biotic), usually applied to an environmental factor, e.g. temperature, rock type or aspect, that affects plant growth or animal distribution.
Acid rainRain containing abnormally high levels of acid, caused by pollutant gases - sulphur dioxide and nitrogen oxides - absorbed by the rain
Acidification processAcidification is the process whereby air pollution, ammonia, sulphur dioxide and nitrogen oxides is converted into acid substances.  The best example is 'acid rain' which damages forests, lakes, freshwater and coastal ecosystems, soils and groundwater.
Advection fogAdvection fog occurs when warm air is chilled to saturation point by travelling over a cool surface.
Agenda 21A key output of the Rio Earth Summit in 1992, looking at the actions required by the world for sustainable development – meeting the needs of today without compromising the ability of future generations to meet their needs – to be achieved. In total, 179 countries were signatories to this common commitment.
Agriculture censusA census of agricultural in Britain carried out annually. The census is a valuable source of data on land use, although weak on socioeconomic aspects.
AlluvialAlluvial deposits (known as alluvium) can consist of a whole range of particles from boulders down through cobbles, pebbles, gravel, sand, silt, and clay. The raw materials are the rocks and soils of upland areas that are loosened by erosion and washed away by mountain streams.
Anabatic windsLocal valley winds, blowing uphill during the day, as the land is heated.
Ancient MonumentA scheduled site of historical and cultural significance, managed by Historic Scotland.
AnemographAn anemograph records the direction and velocity of surface wind.
AnticycloneAn area of high pressure associated with light winds blowing in a clockwise direction in the northern hemisphere. Normally associated with stable, bright weather.
Arctic-alpineVery cold climate conditions found in the Arctic and alpine regions
AspectThe compass direction a hill slope faces.

A rapid flow of snow down a slope, typically mountainous terrain, from either natural triggers or human activity.