Higher air temperatures also increase the concentration of onzone at ground level. Ozone damages lung tissue, and causes particular problems for people with asthma and other lung diseases. In much of the nation, a warming of four degrees (F) could increase ozone concentrations by about 5 percent.

Warmer temperatures may increase the number of people who die each year from cold weather. However, in the United States, only 1000 people die from the cold each year, while twice that many die from the heat.

Global warming may also increase the risk of some infectious diseas, particular those diseases that only appear in warm areas. Diseases that are spread by mosquitos and other insects could become more prevalent if warmer temperatures enabled those insects to become established farther north.

In spite of these risks, increased mortality is not an inevitable consequence of global warming. Malaria, for example, is rare in the United States even in warmer regions where the mosquito that transmits the disease is found, because this nation has the ability to rapidly identify and contain outbreaks when they appear.

Water resources

Changing climate is expected to increase both evaporation and precipitation in most areas of the United States. In those areas where evaporation increases more than precipitation, soil will become drier, lake levels will drop, and rivers will carry less water.

Lower river flows and lower lake levels could impair navigation, hydroelectric power generation, and water quality, and reduce the supplies of water available for agricultural, residential and industrial uses.

Warmer temperatures would cause the snow to melt earlier and thus reduce summer supplies even if rainfall increased during the spring. More generally, the tendency for rainfall to be more concentrated in large storms as temperatures rise would tend to increase river flooding, without increasing the amount of water available.

Forests

The projected 2°C warming could shift the ideal range for many North American forests species by about 300km to the north. If the climate changes slowly enough, warmer temperatures may enable the trees to colonize north into areas that are currently too cold , at about the same rate as southern areas became too hot and dry for the species to survive. If the earth warms 2°C in 100 years, however, the species would have to migrate about 2 miles every year.

Trees whose seeds are spread by birds may are able to spread at that rate. But neither trees whos seeds are carried by the wind. Poor soils may also limit the rate at which tree species can spread north. Those, the range over which a particular species is found may tend to be squeezed as southern areas become inhospitably hot. The net result is that some forets may tend to have a less diverse mix of tree species.

Coastel Zones

Sea level is rising more rapidly along the US coast than worldwide. Studies have estimated that along the Gulf and Atlantic coasts, a 30cm rise in sea level is likely by 2050 and could occur as soon as 2025. in next century, a two foot rise is most likely, but a four foot rise is possible. The sea level will probably continue to rise for several centuries, even if global temperatures were stop rising a few decades hence.

Rising sea level inundates wetlands and other low-lying lands, erodes beaches, intensifies flooding, and increases the salinity of rivers, bays, and groundwater tables.

Coastel marshes and swamps are particular vulnerable to rising sea level because they are mostly withhin a few feet of sea level. As the sea rises, the outer boundary of these wetlands will erode, and new wetlands will form inland as previosly dry areas are flooded by the higher water levels. A higher sea level raises the flood level from a storm of given severity. A 3-foot rising sea level (for example) would enable a 15-year storm to flood many areas that today are only flooded by a 100-year storm.

Coastal flooding is also exacerbated by increasing rainfall intensity. Along tidal rivers and in

extremely flat areas, floods can caused by storm surges from the sea or by a river surges.

Finally, rising sea level tends to increase the salinity of both surface water and ground water.

The class of aquifers that most vulnerable to risinig sea level are those that are recharged in

areas that are cussently fresh but which could become salty in the future.