10 April 2007

Working Group II (WGII) of the UN Intergovernmental Panel on Climate Change (IPCC) has released its contribution to the newest assessment of climate change science—the IPCC Fourth Assessment Report (AR4) “Climate Change 2007”. This second part of the report, titled “Climate Change Impacts, Adaptation and Vulnerability”, focuses on current scientific understanding of impacts of climate change on natural, managed and human systems, the capacity of these systems to adapt and their vulnerability.

Projections have been made on future impacts of climate change in the following areas:

  • Fresh water resources—By mid-century, annual average river runoff and water availability will increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics, some of which are presently water stressed areas. Drought-affected areas will likely increase in extent. Heavy precipitation events, which are very likely to increase in frequency, will augment flood risk.
  • Ecosystems—The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of climate change, associated disturbances (e.g., flooding, drought, wildfire, insects, ocean acidification), and other global change drivers (e.g., land use change, pollution, over-exploitation of resources). Approximately 20-30% of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5°C.
  • Food, fibre and forest products—Crop productivity is projected to increase slightly at mid to high latitudes for local mean temperature increases of up to 1-3°C depending on the crop, and then decrease beyond that in some regions. At lower latitudes, especially seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2°C), which would increase risk of hunger.
  • Coastal systems—Coasts are projected to be exposed to increasing risks, including coastal erosion, due to climate change and sea-level rise and the effect will be exacerbated by increasing human-induced pressures on coastal areas. Coastal wetlands including salt marshes and mangroves are projected to be negatively affected by sea-level rise.
  • Industry, settlement and society—Costs and benefits of climate change for industry, settlement, and society will vary widely by location and scale. In the aggregate, net effects will tend to be more negative the larger the change in climate. The most vulnerable industries, settlements and societies are those in coastal and river flood plains, those whose economies are closely linked with climate-sensitive resources, and those in areas prone to extreme weather events. Poor communities can be especially vulnerable, in particular those concentrated in high-risk areas.
  • Health—Climate change-related exposures are likely to affect the health status of millions of people through a variety of impacts, including increases in malnutrition; increased deaths, disease and injury due to heat waves, floods, storms, fires and droughts; increased burden of diarrhoeal disease; and increased frequency of cardio-respiratory diseases due to higher concentrations of ground level ozone related to climate change.

The report also includes future climate change impact projections on a regional basis, for the continents and for small islands, the latter believed to be particularly vulnerable.

  • Africa is one of the most vulnerable continents because of multiple stresses and low adaptive capability. By 2020, between 75 and 250 million people in Africa may be exposed to an increase of water stress due to climate change.
  • Asia will be affected by decreases in fresh water availability which could affect more than a billion people by the 2050s. Glacier melt in the Himalayas will cause increase in flooding, rock avalanches from destabilized slopes, and decreased river flows as the glaciers recede. Coastal areas in South, East and Southeast Asia will be at greatest risk due to increased flooding from the sea and in some mega-deltas flooding from the rivers. Crop yields could increase up to 20% in East and Southeast Asia, but they will decrease up to 30% in Central and South Asia by the mid-21st century.
  • Europe will see increased risk of flooding and increased coastal erosion due to storminess and sea level rise. Mountainous areas will face glacier retreat, reduced snow cover and winter tourism, and extensive species losses.
  • North America will experience decreased snowpack in the western mountains, more winter flooding, and reduced summer flows, exacerbating competition for water resources. Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an extended period of high fire risk. Cities that currently experience heat waves will be further challenged by an increased number, intensity and duration of heat waves. Coastal communities and habitats will be stressed by climate change impacts interacting with development and pollution.
  • Latin America: By mid-century, increases in temperature and associated decreases in soil water are projected to lead to gradual replacement of tropical forest by savanna in eastern Amazonia. In drier areas, climate change may lead to salinisation and desertification of agricultural land. Changes in precipitation patterns and the disappearance of glaciers are projected to affect water availability for human consumption, agriculture and energy generation.
  • Australia will experience water security problems and significant loss of biodiversity.
  • Small Islands, located in the tropics or at higher latitudes, are especially vulnerable to the effects of climate change, sea level rise and extreme events. Coastal deterioration is projected to impact local resources and tourism. Climate change is also projected by the mid-century to reduce water resources in many small islands (e.g., in the Caribbean and Pacific) to the point where they become insufficient to meet demand during low rainfall periods.

The first part of the Climate Change 2007 assessment, “The Physical Science Basis”, was released in February 2007. Third and final part of the report, discussing mitigation of climate change, will be released in May.

Source: IPCC (WGII Summary for Policymakers)