Climate Change Information Sheet 12
Biological diversity and ecosystems
- Biological diversity - the source of enormous environmental, economic, and cultural value - will be threatened by rapid climate change. A warming of 13.5oC over the next 100 years would shift current climate zones poleward by approximately 150550 km - and vertically by 150550 m - in mid-latitude regions. The composition and geographic distribution of unmanaged ecosystems will change as individual species respond to new conditions. At the same time, habits will be degraded and fragmented by the combination of climate change, deforestation, and other environmental pressures. Species that cannot adapt quickly enough may become extinct - an irreversible loss.
- Forests adapt slowly to changing conditions. Observations, experiments, and models demonstrate that a sustained increase of just 1oC in the global average temperature would affect the functioning and composition of forests. A typical climate change scenario for the 21st century shows a major impact on the species composition of one third of the world's existing forests (varying by region from one seventh to two thirds). Entire forest types may disappear, while new combinations of species, and hence new ecosystems, may be established. Other stresses caused by warming may include more pests, pathogens, and fires. Because higher latitudes are expected to warm more than equatorial ones, boreal forests will be more affected than temperate and tropical forests.
- Forests play an important role in the climate system. They are a major reservoir of carbon, containing some 80% of all the carbon stored in land vegetation, and about 40% of the carbon residing in soils. Large quantities of carbon may be emitted into the atmosphere during transitions from one forest type to another because mortality releases carbon faster than growth absorbs it. Forests also directly affect climate on the local, regional, and continental scales by influencing ground temperature, evapo-transpiration, surface roughness, albedo (or reflectivity), cloud formation, and precipitation.
- Deserts and arid and semi-arid ecosystems may become more extreme. With few exceptions, deserts are projected to become hotter but not significantly wetter. Higher temperatures could threaten organisms that now exist near their heat-tolerance limits.
- Rangelands may experience altered growing seasons. Grasslands support approximately 50% of the world's livestock and are also grazed by wildlife. Shifts in temperatures and precipitation may reshape the boundaries between grasslands, shrublands, forests, and other ecosystems. In tropical regions such changes in the evapo-transpiration cycle could strongly affect productivity and the mix of species.
- Mountain regions are already under considerable stress from human activities. The projected declines in mountain glaciers, permafrost, and snow cover will further affect soil stability and hydrological systems (most major river systems start in the mountains). As species and ecosystems are forced to migrate uphill, those whose climatic ranges are already limited to mountain tops may have nowhere to go and become extinct. Agriculture, tourism, hydropower, logging, and other economic activities will also be affected. The food and fuel resources of indigenous populations in many developing countries may be disrupted.
- The cryosphere will shrink. Representing nearly 80% of all freshwater, the cryosphere encompasses all of the earth's snow, ice, and permafrost. Frozen water is, of course, highly sensitive to temperature change (a fact that researchers have used for studying past climate changes). Climate models project that mountain glaciers could be reduced by one third to one half over the next 100 years. This in turn will affect nearby ecosystems and communities as well as seasonal river flows and water supplies Cwhich in turn would affect hydropower and agriculture. The landscapes of many high mountain ranges and polar regions would change dramatically. The melting of permafrost could destabilize infrastructure and release additional carbon and methane into the atmosphere. Reduced sea-ice would open certain rivers and coastal areas to navigation for longer seasons. Despite these many striking effects, the Greenland and Antarctic ice sheets are not expected to change much over the next 50100 years.
- Non-tidal wetlands will also be reduced. These open-water and waterlogged areas provide refuge and breeding grounds for many species. They also help to improve water quality and control floods and droughts. Studies from several countries suggest that a warmer climate will contribute to the decline of wetlands through higher evaporation. By altering their hydrological regimes, climate change will influence the biological, biogeochemical, and hydrological functions of these ecosystems, as well as their geographical distribution.
- Human actions can help natural ecosystems adapt to climate change. Creating natural migration corridors and assisting particular species to migrate could benefit forest ecosystems. Reforestation and the "integrated management" of fires, pests, and diseases can also contribute. Rangelands could be supported through the active selection of plant species, controls on animal stocking, and new grazing strategies. Wetlands can be restored and even created. Desertified lands may adapt better if drought-tolerant species and better soil conservation practices are encouraged.
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