The Intergovernmental Panel on Climate Change (IPCC) has recently completed its Third Assessment Report (TAR). The TAR includes an assessment of climate change impacts on ecosystems, food and water resources, human settlements and human health. This represents a review of considerable breadth, incorporating research from throughout the natural and social sciences.

Observed changes in regional climate during the 20th century have led to impacts on sea level, ice and snow cover, permafrost, growing season length, and plant and animal ranges and lifecycles. Examples include coral reef bleaching, shifts in timing of peak stream flow, and longer growing seasons in Europe and the Arctic. Economic damage from extreme weather and climatic events have been increasing, but there are socio-economic factors influencing this trend along with regional climatic factors. Any consideration of future climate-related impacts must therefore account for changes to both natural and human systems. Future economic development choices will influence both greenhouse gas emissions and vulnerabilities to climate.

Projected increases in atmospheric concentrations of greenhouse gases are expected to result in a warmer climate in all regions, with increases in precipitation in many regions (especially high latitudes and Asia), and decreases in some tropical and subtropical areas (such as Central America and southern Africa). These projected changes vary among the different scenarios of greenhouse gas emissions, with large emission increases leading to greater rates of warming. Projections of future impacts are sensitive to these scenarios. A modest warming of less than 1-2°C would lead to increased risks to some ecosystems (such as alpine tundra) and human settlements that are already vulnerable (such as semi-arid and low lying coastal areas) while some areas could benefit (such as high latitude croplands). A greater amount of warming would increase the risk of adverse impacts throughout the world. Major concerns include increased frequency of ecosystem disturbance by fire and insects, expansion of vector- and water-borne diseases, substantial loss of glaciers, changes in water resources, and increased risk of coastal flooding. These and other impacts will challenge national and international capacities to adapt to climate-related opportunities and risks.