Possible collapse of the thermohaline current

The thermohaline current, or THC, acts like a giant global conveyor belt that moves warm water to colder areas of the ocean and cold water to warmer areas of the ocean. In effect, the THC helps global moderate temperatures by warming cold areas and cooling warm areas. Without a functioning THC, the northern hemisphere would be much, much cooler. Scientists now believe, for example, that a collapse of the THC may have caused the last glacial ice age.

Because the THC is dependent upon the balance of salt in the water, adding a large amount of fresh water to the oceans could cause another collapse of the THC to occur. Unfortunately, climate change is melting glaciers and the polar ice sheets, in which a huge amount of fresh water is stored.

Widespread plant and animal extinctions

Climate change threatens to result in widespread plant and animal extinctions. Unlike humans societies, natural ecosystems can only cope with and adapt to dramatic climatic changes very slowly. Because the rate of climate change will likely exceed the speed with which natural adaptation can occur, many species will be unable to survive as average global temperatures rapidly rise.

This threat to natural ecosystems is particularly severe because development has already reduced species populations, fragmented ecosystems and placed them under stress from pollution, and introduced barriers to migration, such as communities, farms, roads, and dams.

In the coming years climate change is expected to result in the loss of many coral reefs, coastal wetlands, endangered species (particularly those with limited range and mobility), cool- and cold-water fish, and boreal and alpine forest species. Indeed, one study predicts that 18% to 35% of a sample of 1,103 animal and plant species will be extinct by 2050.

Impacts to human health

Human health around the world will likely be affected by:

• rising levels of heat-related mortality (heat stroke, etc.)
• increased transmission of infectious diseases
• more intense and frequent extreme weather events
• decreases in air quality (particularly if ozone precursors are not further reduced).

While impacts on human health will be experienced around the entire globe, they are expected to be more pronounced in the developing world and in especially vulnerable populations (e.g. the elderly).

Threatened Water Supplies

Water resources throughout the world will be directly affected by climate change through changes in precipitation, evaporation, and snowmelt. While, on average, global precipitation will increase with climate change, some areas will see far less precipitation. Moreover, seasonal precipitation patterns could be greatly intensified, leading to both more winter precipitation and less summer precipitation.

Thus, while some regions could benefit from increased supplies, they may also suffer from a greatly increased incidence of major floods. Many others will experience increased droughts.

Economic Disruptions

Different economic sectors will be affected by climate change in a variety of ways.

For example:

• Agriculture will be affected by changes in temperature and precipitation patterns, altered distribution of pests and diseases, as well as potentially reduced availability of water supplies for irrigation.
• Forestry will be impacted changes in climate, pests, and disease.
• Coastal development and low-lying coastal areas will be at risk from flooding by rising seas, as well as subject to beach erosion and increased intensity and frequency of storms.

However, given the extent to which the global economy is dependent upon climate and weather patterns, virtually every sector of the economy will be impacted by climate change either directly or indirectly.