Direct impacts
One of the most easily imagined impacts of global warming is an increase in the number and severity of heat waves. Heat stress is a well-known danger during prolonged bouts of hot weather, especially in cities, which tend to trap heat. In both New York and Shanghai, for instance, records show that daily mortality rates increase sharply once temperatures exceed a certain threshold [273]. During intense heat waves, the death toll attributed to heat stress can be surprisingly high, as occurred in Chicago in July 1995, when heat stress killed 726 people during a 4-day heat wave [274] [275].
Midlatitude cities including Washington, D.C., Athens, and Shanghai seem to be at greatest risk for deadly heat waves. In these cities, residents (especially the elderly, the very young, and the poor) are not acclimatized to extremely hot weather and are thus more vulnerable to heat stress. Among these vulnerable groups, the existence of previous health problems, greater heat exposure due to substandard housing, and lack of access to air conditioning are all factors leading to higher heat-related mortality. By the middle of the next century, climate change could increase the frequency of very hot days severalfold in a city similar to Washington, D.C., according to one estimate [276]. The normally hotter average temperatures in tropical and subtropical cities seem to help residents accommodate heat waves better, so they suffer fewer heat-stress problems, although heat-related deaths during a 1995 heat wave in New Delhi indicate that even residents in the tropics can be susceptible to extreme temperatures [277].
Conversely, a potential health benefit of warmer global temperatures could be fewer cold-related deaths as winters become milder. A recent British study estimated that by 2050, an increase in the average wintertime temperature by 2.0° C to 2.5° C, as predicted by some climate models, might result in as many as 9,000 fewer cold-related deaths per year in England and Wales. Yet, this decrease in winter mortality would probably only partially offset additional heat-related deaths; studies indicate that higher mortality is generally associated with heat waves than cold spells [278].
In addition to more frequent heat waves, global climate change is expected to result in greater weather variability overall. In particular, climatologists believe that relatively small changes in the average global climate in the future could produce large changes in the frequency of extreme weather events [279], such as hurricanes (cyclones), violent thunderstorms, and windstorms. Through flood and wind damage, these natural disasters already exact a heavy burden in the destruction of lives and property [280].
Rising sea levels, another expected consequence of global warming, could adversely affect the health and well-being of coastal inhabitants. Sixteen of the world’s largest cities with populations of more than 10 million are located in coast al zones, and coastal populations are increasing rapidly worldwide. The IPCC projects that sea level will rise between 0.3 and 1.0 meter by 2100, with a best-guess estimate of 0.5 meter [281].
The most immediate threat from such a rise would be to those who live directly on the coast, in low-lying areas such as river deltas, or on small island nations such as the Maldives, the Marshall Islands, Kiribati, and Tonga, where land is virtually all within a few meters of sea level already. Rising seas would inundate many of these islands, increase storm damage to the remaining land, and contaminate the freshwater supplies found in island aquifers [282].
Delta regions such as the Ganges-Bramaputra delta in Bangladesh, the Nile delta in Egypt, or the Niger delta in Nigeria could also suffer a similar fate. The situation in Bangladesh’s densely settled Ganges-Bramaputra delta is probably the most serious. A recent study projects that a 1-meter sea rise could inundate 17 percent of Bangladesh’s total land area and displace some 11 million people (at current population densities). In the Nile delta, a 1-meter rise would displace around 6 million people unless costly protection efforts were mounted; and in the Niger delta, a similar rise would inundate 15,000 square kilometers of land and force about one half million people to relocate [283]. (See Rising Sea Levels Could Displace Millions of Coastal Residents.)
References and notes
273. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 43-44.
274. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), p. 9.
275. “Heat Related Mortality – Chicago, July, 1995,” Morbidity and Mortality Weekly Report, Vol. 44, No. 31 (August 11, 1995).
276. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 50-52, 54.
277. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), p. 9.
278. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 53-54.
279. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 123-124.
280. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 33-34, 123.
281. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 145, 148.
282. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 152-153.
283. A. McMichael et al., eds., Climate Change and Human Health (World Health Organization, Geneva, 1996), pp. 153-156.
