Health - The prevalence of some diseases and other threats to human health depend largely on local climate. Extreme temperatures (hot or cold) can directly lead to loss of life, while climate-related disturbances in ecological systems, such as changes in the range of disease-carrying insects, can impact the incidence of infectious diseases. In addition, warm temperatures can increase air and water pollution, which in turn harm human health.

Agriculture and Food Supply - Agriculture is highly sensitive to climate variability and weather extremes, such as droughts, floods, severe storms, and prevalence of pests. While food production may benefit from a warmer climate and even a CO2 fertilization effect, the increased potential for droughts, floods and heat waves will pose challenges for farmers. Enduring changes in climate, water supply and soil moisture could make it less feasible to continue crop production in certain regions. Other forms of food production, such as marine fisheries, may be vulnerable as well due to rising ocean temperatures and loss of breeding habitat for critical species.

Forests - The prevalence of some diseases and other threats to human health depend largely on local climate. Extreme temperatures (hot or cold) can directly lead to loss of life, while climate-related disturbances in ecological systems, such as changes in the range of disease-carrying insects, can impact the incidence of infectious diseases. In addition, warm temperatures can increase air and water pollution, which in turn harm human health.

Ecosystems and Biodiversity - An ecosystem is an interdependent, functioning system of plants, animals and microorganisms. An ecosystem can be as large as the Mojave Desert or as small as a local pond. Without the support of the other organisms within their own ecosystem, life forms cannot survive, much less thrive. Such support requires that predators and prey, fire and water, food and shelter, clean air and open space remain in balance with each other and with the environment around them. Climate is an integral part of ecosystems and organisms have adapted to their regional climate over time. Climate change is a factor that has the potential to alter ecosystems and the many resources and services they provide to each other and to society. Human societies depend on ecosystems for the natural, cultural, spiritual, recreational and aesthetic resources they provide.

Coastal Zones & Sea Level Rise - Higher temperatures are expected to further raise sea levels by expanding ocean water, melting mountain glaciers and small ice caps and causing portions of Greenland and the Antarctic ice sheets to melt. The Intergovernmental Panel on Climate Change (IPCC) estimates that the global average sea level will rise between 0.3 and 2.9 feet (0.09 to 0.88 meters) in the next century (IPCC, 2001). The range reflects uncertainty about global temperature projections and how rapidly ice sheets will melt or slide into the ocean in response to the warmer temperatures. Considering the projections and current land subsidence, most coastal scientists focus on the possible impacts of a one to three foot rise in sea level over the next century; an amount sufficient to directly impact development and habitability in many coastal regions. Rising seas will inundate low-lying lands, erode beaches, intensify flooding and increase the salinity of rivers, bays and groundwater tables.

Water Resources - Increasing temperatures are very likely to lead to changes in precipitation and atmospheric moisture. Trends so far seem to indicate less frequent precipitation events, but events of greater intensity. Many communities, particularly in the western United States, depend on meltwater from snowpack in the mountains to sustain supplies of drinking water through the dry summer months. Reduced river and stream flow will also restrict water for irrigation and hydroelectric power generation.

Extreme Storms - Climate is defined not simply as average temperature and precipitation, but also by the type, frequency and intensity of weather events. Climate change has the potential to alter the prevalence and severity of extremes such as heat waves, cold waves, storms, floods and droughts. Though predicting changes in these types of events under a changing climate is difficult, understanding vulnerabilities to such changes is a critical part of estimating future climate impacts on human health, society and the environment.

Global Social and Political Stability - There is increasing evidence that the impacts of rising sea levels, crop failures and increasingly violent storm activity will hit poor countries near the equator harder than the rich countries of the world. This raises the spectre of large refugee migrations and widespread political unrest around the world. Many of the most-populated regions of the developing world are in low-lying river deltas of Asia and the Middle East, areas likely to be severely impacted by the effects of climate change.

Global Economic Activity - The Stern Report, published by the UK Treasury Office, estimates that the economic effects of climate change could be as high as 20% of global GDP each year. According to the report: "Our actions now and over the coming decades could create risks of major disruption to economic and social activity, on a scale similar to those associated with the great wars and the economic depression of the first half of the 20th century."