Rising Sea Level
Some observers compare global warming to nuclear war in its potential to disrupt human and environmental systems. While some sources dispute the occurrence of human-induced climate change, if temperature increases of 1.5 to 4.5 degrees Celsius (35 to 40 degrees Fahrenheit) were to take place, substantial changes would occur on Earth's surface. If average temperatures rise this much by 2030, the global sea level could rise 20 to 140 centimeters (8 to 56 inches). The Climate Institute in Washington, D.C., forecasts a further rise of 26 inches by 2100. This rise would be caused by the expansion of seawater as it is warmed, along with melting glaciers and ice caps.
More than half the population of the United States lives within 50 miles of a coastline. A rising sea level would narrow or destroy beaches, flood wetland areas, and either submerge or force costly fortification of shoreline property. Figure 2.5 shows areas along the Southeast coast that could be vulnerable to rising sea levels because they lie at low elevations.
Higher water levels would increase storm damage and many coastal cities worldwide would be flooded. Some islands, such as the Philippines, have already seen encroachment. Residents of the Maldives, islands which lie on average three feet above sea level in the Indian Ocean, are already erecting artificial defenses, such as breakwaters made of concrete, to fend off rising seas.
Some 70 million people in low-lying areas of Bangladesh could be displaced by a one-meter (39.4 inches) rise. Such a rise would also threaten Tokyo, Osaka, and Nagoya in Japan, as well as coastal China and the Atlantic and Gulf Coasts of the United States. The rising waters would also intrude on inland rivers, threatening fresh water supplies and increasing the salt content of groundwater as the sea encroaches on freshwater aquifers (naturally occurring underground water reservoirs). Much of the increased rainfall would come not in the steady, gentle rains favored by farmers, but from heavy storms and flooding.
Increased Heat
Warmer temperatures may also increase the evaporation rate, thereby increasing atmospheric water vapor and cloud cover, which in turn may affect regional rainfall patterns. A warmer climate would likely shift the rain belt of the middle latitudes toward the poles as water-laden air of the tropics travels further toward the poles before the moisture condenses as precipitation. This would shift patterns of rainfall around the world. Wetter, more violent weather is projected for some regions. Forests, which are adapted to a narrow temperature and moisture range, would particularly be threatened by climate shifts.
The opposite problem—too little water—could worsen in arid areas such as the Middle East and parts of Africa. Some experts have suggested that the greenhouse effect and global warming are mild terms for a coming era that may be marked by heat waves that may make some regions virtually uninhabitable. Frequent droughts could plague North America and Asia, imperiling food production, as agriculture is particularly vulnerable to the effects of climate change. Most experts believe Africa will be the most vulnerable to climate change because its economy depends largely on rain-fed agriculture, and many farmers are too poor and ill equipped to adapt. Australia and Latin America could also be subject to severe drought.
NASA has begun using computer calculations in an attempt to predict the effects of global warming on some of the major cities in the United States.
The Effect of Increased Temperatures on Humans
Extra heat alone would be enough to kill some people. Some deaths would occur directly from heat-induced strokes and heart attacks. Air quality also deteriorates as temperatures rise. Hot, stagnant air contributes to the formation of atmospheric ozone, the main component of smog, which damages human lungs. Poor air quality can also aggravate asthma and other respiratory diseases. Increasing ultraviolet rays can increase the incidence of skin cancers, diminish the function of the human immune system, and cause eye problems such as cataracts. Higher temperatures and added rainfall could create ideal conditions for the spread of a host of infectious diseases by insects, including mosquito-borne malaria, dengue fever, and encephalitis.
Decreasing Biological Diversity
Biological diversity is also predicted to suffer from global warming. Loss of forests, tundra (arctic plains), and
FIGURE 2.5
Areas of the Gulf Coast lying at low elevations that are vulnerable to sea level rise
wetlands could irrevocably damage ecosystems. Some species that live in precise, narrow bands of temperature and humidity may find their habitats wiped out altogether. Rising seas would cover coastal mangrove swamps, causing the loss of many species, including the Bengal tiger. Plants and animals of the far north, like the polar bear and the walrus, would die out for lack of an acceptably cold environment. Many species cannot migrate rapidly enough to cope with climate change at the projected rate. Opportunistic species, such as weeds, often out-compete trees and other plants more valued by humans. Pests, such as certain insects, may survive where other species cannot.
The U.S. Forest Service believes that eastern hemlock, yellow birch, beech, and sugar maple forests would gradually shift their ranges northward by 300 to 600 miles but would be severely limited by the warming and largely die out, along with the wildlife they shelter. Studies by World Wildlife Fund International report that more than half the world's parks and reserves could be threatened by climate change. These include the Florida Everglades, Yellowstone National Park, the Great Smoky Mountains, and Redwood National Park in California. The EPA warned in 1988: "If current trends continue, it is likely that climate may change too quickly for many natural systems to adapt."
SOME POSSIBLE POSITIVE EFFECTS.
There are several possible positive consequences of global warming. Agriculture in the northern United States and southern Canada, on the West Coast, and in interior parts of the West could benefit, as could the evergreen forests of the West Coast. Milder winters could reduce the number of cold-weather deaths, as well as the cost of snow clearance and heating. Northern waters could remain open longer for navigation, and the Arctic Ocean might become ice-free, opening a new trade route between Europe and Asia.
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