Impacts on Terrestrial Ecosystems

The IPCC report points out that ecosystems contain the earth's entire reservoir of genetic material and species diversity. They can be thought of as providing both goods and services that are essential to human individuals and societies. The report lists the following services rendered by ecosystems:

• providing food, fiber, medicines, and energy
• processing and storing carbon and other nutrients
• regulating water runoff, thereby suppressing soil erosion and impacts of floods
• assimilating wastes and purifying water
• providing opportunities for recreation and tourism

The accompanying diagram shows the dependence of various biomes (vegetation types) on temperature and precipitation. Temperature changes of 2 to 4 degrees C or precipitation changes of 200 mm per year can cause significant changes in the boundary regions between these biomes.

1. Forests

   Forests play a particularly unique role because of their long time scale for change, their role as repository of 80% of all above-ground vegetative carbon and 40% of below ground carbon, and their role as hosts to two thirds of the planet's biodiversity. Global warming at a rate of 1.5 to 3.5 degrees over the next 100 years is equivalent to a poleward shift of isotherms of 150 to 550 km or 150 to 550 m altitude shift in mountainous areas over the same period. Typical forest migration rates, by contrast, are estimated to be 4 to 200 km per century.

2. Rangelands

   Rangelands are sometimes defined as unimproved grasslands, shrublands, savannas, deserts, and tundra. They occupy 51% of the earth's land surface and contain about 36% of the total living and dead plant carbon. Small changes in extreme temperatures and precipitation have disproportionately large effects in these regions because of the vulnerability to water availability and water balance.

3. Deserts

   Deserts are characterized by extremely high temperatures and extremely low rainfall. These extremes are likely to increase under climate change. Desertification is defined as land degradation in naturally dry areas resulting from various factors including climate variations and human activities. Desertification is more likely to be irreversible if the environment becomes drier.

4. Cryosphere

   Regions of snow, ice, and permafrost comprise the cryosphere. These regions have provided some of the most notable indications of global warming over the last century. Changes in the cryosphere produce changes in water availability from melt water for cities, agriculture and hydroelectric power generation. Reduction in high-latitude ice fields change global albedo and allow thawing permafrost to release methane hydrates.

5. Mountain regions

   Warming in mountain regions changes snow cover and may impact water supplies, tourism, logging, and hydropower production. Ecosystems unique to specific mid-slope locations may migrate upslope in a warmer climate, but ecosystems indigenous to mountain-top locations have nowhere to migrate under such changes.

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