2.4 Climate and biomesIB Environmental Systems and Societies SL: Revision notes

Climate describes atmospheric conditions over relatively long periods; weather describes conditions over a short period. A biome is a group of comparable ecosystems that have developed in similar climatic conditions wherever they occur. Abiotic factors, mainly temperature and precipitation, are the determinants of terrestrial biome distribution.

Biomes can be grouped as freshwater, marine, forest, grassland, desert and tundra.

The tricellular model explains the behaviour of the atmosphere and the distribution of precipitation and temperature at different latitudes. Each hemisphere has three cells: Hadley, Ferrel and polar.

At the equator intense solar heating makes air rise, cool and condense, giving a low-pressure zone with heavy rain (tropical rainforest). At about 30° north and south air descends, warming and drying, giving high pressure and deserts. Around 60° air rises again, giving rain and temperate forest, and at the poles cold air descends, giving cold, dry conditions (tundra and ice).

The oceans absorb solar radiation, and ocean currents distribute the resulting heat around the world. The warm North Atlantic Drift, for example, keeps north-western Europe much warmer than places at the same latitude in Canada. Changes to currents would therefore change regional climates and biomes.

Global warming is changing climates and so shifting biomes: treelines move north and uphill, tundra shrinks as shrubs and trees spread, and tropical biomes may expand toward the poles. Species adapted to the old conditions may lose habitat. Permafrost thaw releases greenhouse gases, a positive feedback.