Ecosystems are of fundamental importance to environmental function and to sustainability,
and they provide many goods and services critical to individuals and societies.
These goods and services include: (i) providing food, fiber, fodder, shelter,
medicines, and energy; (ii) processing and storing carbon and nutrients; (iii)
assimilating wastes; (iv) purifying water, regulating water runoff, and moderating
floods; (v) building soils and reducing soil degradation; (vi) providing opportunities
for recreation and tourism; and (vii) housing the Earth's entire reservoir of
genetic and species diversity. In addition, natural ecosystems have cultural,
religious, aesthetic, and intrinsic existence values. Changes in climate have
the potential to affect the geographic location of ecological systems, the mix
of species that they contain, and their ability to provide the wide range of
benefits on which societies rely for their continued existence. Ecological systems
are intrinsically dynamic and are constantly influenced by climate variability.
The primary influence of anthropogenic climate change on ecosystems is expected
to be through the rate and magnitude of change in climate means and extremes-climate
change is expected to occur at a rapid rate relative to the speed at which ecosystems
can adapt and reestablish themselves-and through the direct effects of increased
atmospheric CO2 concentrations, which may increase the productivity and efficiency
of water use in some plant species. Secondary effects of climate change involve
changes in soil characteristics and disturbance regimes (e.g., fires, pests,
and diseases), which would favor some species over others and thus change the
species composition of ecosystems.
|The ultimate objective of this Convention and any related legal instruments that the Conference of the Parties may adopt is to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system. Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.|
Based on model simulations of vegetation distribution, which use GCM-based climate scenarios, large shifts of vegetation boundaries into higher latitudes and elevations can be expected. The mix of species within a given vegetation class likely will change. Under equilibrium GCM climate scenarios, large regions show drought-induced declines in vegetation, even when the direct effects of CO2 fertilization are included. By comparison, under transient climate scenarios-in which trace gases increase slowly over a period of years-the full effects of changes in temperature and precipitation lag the effects of a change in atmospheric composition by a number of decades; hence, the positive effects of CO2 precede the full effects of changes in climate.
Climate change is projected to occur at a rapid rate relative to the speed at which forest species grow, reproduce, and reestablish themselves (past tree species' migration rates are believed to be on the order of 4-200 km per century). For mid-latitude regions, an average warming of 1-3.5°C over the next 100 years would be equivalent to a poleward shift of the present geographic bands of similar temperatures (or "isotherms") approximately 150-550 km, or an altitude shift of about 150-550 m. Therefore, the species composition of forests is likely to change; in some regions, entire forest types may disappear, while new assemblages of species and hence new ecosystems may be established. As a consequence of possible changes in temperature and water availability under doubled equivalent-CO2 equilibrium conditions, a substantial fraction (a global average of one-third, varying by region from one-seventh to two-thirds) of the existing forested area of the world likely would undergo major changes in broad vegetation types-with the greatest changes occurring in high latitudes and the least in the tropics. In tropical rangelands, major alterations in productivity and species composition would occur due to altered rainfall amount and seasonality and increased evapotranspiration, although a mean temperature increase alone would not lead to such changes.
Inland aquatic ecosystems will be influenced by climate change through altered water temperatures, flow regimes, water levels, and thawing of permafrost at high latitudes. In lakes and streams, warming would have the greatest biological effects at high latitudes-where biological productivity would increase and lead to expansion of cool-water species' ranges-and at the low-latitude boundaries of cold- and cool-water species ranges, where extinctions would be greatest. Increases in flow variability, particularly the frequency and duration of large floods and droughts, would tend to reduce water quality, biological productivity, and habitat in streams. The geographical distribution of wetlands is likely to shift with changes in temperature and precipitation, with uncertain implications for net greenhouse gas emissions from non-tidal wetlands. Some coastal ecosystems (saltwater marshes, mangrove ecosystems, coastal wetlands, coral reefs, coral atolls, and river deltas) are particularly at risk from climate change and other stresses. Changes in these ecosystems would have major negative effects on freshwater supplies, fisheries, biodiversity, and tourism.
Adaptation options for ecosystems are limited, and their effectiveness is uncertain. Options include establishment of corridors to assist the "migration" of ecosystems, land-use management, plantings, and restoration of degraded areas. Because of the projected rapid rate of change relative to the rate at which species can reestablish themselves, the isolation and fragmentation of many ecosystems, the existence of multiple stresses (e.g., land-use change, pollution), and limited adaptation options, ecosystems (especially forested systems, montane systems, and coral reefs) are vulnerable to climate change.
Water availability is an essential component of welfare and productivity. Currently, 1.3 billion people do not have access to adequate supplies of safe water, and 2 billion people do not have access to adequate sanitation. Although these people are dispersed throughout the globe-reflecting sub-national variations in water availability and quality-some 19 countries (primarily in the Middle East and north and southern Africa) face such severe shortfalls that they are classified as either water-scarce or water-stressed; this number is expected to roughly double by 2025, in large part because of increases in demand resulting from economic and population growth. For example, most policy makers now recognize drought as a recurrent feature of Africa's climate. However, climate change will further exacerbate the frequency and magnitude of droughts in some places.
Changes in climate could exacerbate periodic and chronic shortfalls of water, particularly in arid and semi-arid areas of the world. Developing countries are highly vulnerable to climate change because many are located in arid and semi-arid regions, and most derive their water resources from single-point systems such as bore holes or isolated reservoirs. These systems, by their nature, are vulnerable because there is no redundancy in the system to provide resources, should the primary supply fail. Also, given the limited technical, financial, and management resources possessed by developing countries, adjusting to shortages and/or implementing adaptation measures will impose a heavy burden on their national economies. There is evidence that flooding is likely to become a larger problem in many temperate and humid regions, requiring adaptations not only to droughts and chronic water shortages but also to floods and associated damages, raising concerns about dam and levee failures.
The impacts of climate change will depend on the baseline condition of the water supply system and the ability of water resources managers to respond not only to climate change but also to population growth and changes in demands, technology, and economic, social, and legislative conditions.
Various approaches are available to reduce the potential vulnerability of water systems to climate change. Options include pricing systems, water efficiency initiatives, engineering and structural improvements to water supply infrastructure, agriculture policies, and urban planning/management. At the national/regional level, priorities include placing greater emphasis on integrated, cross-sectoral water resources management, using river basins as resource management units, and encouraging sound pricing and management practices. Given increasing demands, the prevalence and sensitivity of many simple water management systems to fluctuations in precipitation and runoff, and the considerable time and expense required to implement many adaptation measures, the water resources sector in many regions and countries is vulnerable to potential changes in climate.
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