Climate Change 2001: Impacts, Adaptation and Vulnerability

Executive Summary

Will the Climate in Asia Change?

Continuing emissions of greenhouse gases from human activities are likely to result in significant changes in mean climate and its intraseasonal and interannual variability in the Asian region. Given the current state of climate modeling, projections of future regional climate have only limited confidence. Currently available general circulation models (GCMs) suggest that the area-averaged annual mean warming would be about 3°C in the decade of the 2050s and about 5°C in the decade of the 2080s over the land regions of Asia as a result of future increases in atmospheric concentration of greenhouse gases. Under the combined influence of greenhouse gas and sulfate aerosols, surface warming would be restricted to about 2.5°C in the 2050s and about 4°C in the 2080s. In general, projected warming over Asia is higher during Northern Hemisphere (NH) winter than during summer for both time periods. The rise in surface air temperature is likely to be most pronounced over boreal Asia in all seasons. GCM simulations project relatively more pronounced increases in minimum temperature than in maximum temperature over Asia on an annual mean basis, as well as during winter, hence a decrease in diurnal temperature range (DTR). During summer, however, an increase in DTR is projected, suggesting that the maximum temperature would have more pronounced increases relative to the minimum temperature. The summertime increase in DTR over central Asia is likely to be significantly higher relative to that in other regions.

In general, all GCMs simulate an enhanced hydrological cycle and an increase in area-averaged annual mean rainfall over Asia. An annual mean increase in precipitation of approximately 7% in the 2050s and approximately 11% in the 2080s over the land regions of Asia is projected from future increases in atmospheric concentration of greenhouse gases. Under the combined influence of greenhouse gases and sulfate aerosols, the projected increase in precipitation is limited to about 3% and 7% in the 2050s and 2080s, respectively. The projected increase in precipitation is greatest during NH winter for both time periods. The increase in annual and winter mean precipitation is projected to be highest in boreal Asia; as a consequence, the annual runoff of major Siberian rivers is expected to increase significantly. Although area-averaged annual mean precipitation is projected to increase in temperate Asia, a decline in summer precipitation is likely over the central parts of arid and semi-arid Asia. Because the rainfall over this region is already low, severe water-stress conditions—leading to expansion of deserts—are quite possible, with rises in surface air temperature and depletion of soil moisture. GCMs show high uncertainty in future projections of winter and summer precipitation over south Asia (with or without aerosol forcings). Because much of tropical Asia is intrinsically linked with the annual monsoon cycle, research into a better understanding of the future behavior of the monsoon and its variability is warranted.

Is Asia Vulnerable to Projected Climate Change?

Climate change-induced vulnerabilities in Asia have to be understood against the backdrop of the physical, economic, and social environment of the countries in the region. They not only provide benchmarks against which vulnerabilities are to be assessed but also the potential for adaptation to them. The socioeconomic environment of many countries in Asia is characterized by high population density and relatively low rates of economic growth. Surface water and groundwater resources in Asian countries play vital roles in forestry, agriculture, fisheries, livestock production, and industrial activity. The water and agriculture sectors are likely to be most sensitive to climate change-induced impacts in Asia. Forest ecosystems in boreal Asia would suffer from floods and increased volume of runoff associated with melting of permafrost regions. The dangerous processes of permafrost degradation resulting from global warming strengthen the vulnerability of all relevant climate-dependent sectors affecting the economy in high-latitude Asia. Although the frequency and severity of floods eventually would increase in many countries of Asia, arid and semi-arid regions of Asia could experience severe water-stress conditions. The stresses of climate change are likely to disrupt the ecology of mountain and highland systems in Asia. Major changes in high-elevation ecosystems of Asia can be expected as a consequence of the impacts of climate change. Many species of mammals and birds and a large population of many other species in Asia could be exterminated as a result of the synergistic effects of climate change and habitat fragmentation. Glacial melt also is expected to increase under changed climate conditions, which would lead to increased summer flows in some river systems for a few decades, followed by a reduction in flow as the glaciers disappear.

Agricultural productivity in Asia is likely to suffer severe losses because of high temperature, severe drought, flood conditions, and soil degradation; food security of many developing countries in the region would be under tremendous threat. There are likely to be large-scale changes in productivity of warmwater and coolwater fish in many countries in Asia. Sea-level rise would cause large-scale inundation along the vast Asian coastline and recession of flat sandy beaches. The ecological security of mangroves and coral reefs around Asia would be put at risk. The monsoons in tropical Asia could become more variable if El Niño-Southern Oscillation (ENSO) events become stronger and more frequent in a warmer atmosphere. Countries in temperate and tropical Asia are likely to have increased exposure to extreme events, including forest die-back and increased fire risk, typhoons and tropical storms, floods and landslide, and severe vector-borne diseases.

Major Risks in Asia from Climate Change

Based on present scientific research, the following risks linked to changes in climate and its variability for Asia are identified:¹

• The dangerous processes of permafrost degradation resulting from global warming would increase the vulnerability of many climate-dependent sectors affecting the economy in boreal Asia. ***

• Surface runoff increases during spring and summer periods would be pronounced in boreal Asia. ***

• The frequency of forest fires is expected to increase in boreal Asia. ***

• The large deltas and coastal low-lying areas of Asia could be inundated by sea-level rise. ****

• The developing countries of temperate and tropical Asia already are quite vulnerable to extreme climate events such as droughts and floods; climate change and its variability could exacerbate these vulnerabilities. ****

• Increased precipitation intensity, particularly during the summer monsoon, could increase flood-prone areas in temperate and tropical Asia. There is a potential for drier conditions in arid and semi-arid Asia during summer, which could lead to more severe droughts. ***

• Freshwater availability is expected to be highly vulnerable to anticipated climate change. ****

• Tropical cyclones could become more intense. Combined with sea-level rise, this impact would result in enhanced risk of loss of life and properties in coastal low-lying areas of cyclone-prone countries of Asia. ***

• Crop production and aquaculture would be threatened by a combination of thermal and water stresses, sea-level rise, increased flooding, and strong winds associated with intense tropical cyclones. ****

• Warmer and wetter conditions would increase the potential for a higher incidence of heat-related and infectious diseases in tropical and temperate Asia. ***

• Climate change would exacerbate threats to biodiversity resulting from land-use/cover change and population pressure in Asia.***