Environmental Engineering Reference
In-Depth Information
than heat-related deaths in the United States, Europe, and almost all
countries outside the tropics, and almost all of them are due to common
illnesses that are increased by cold.
14
From 1979 to 1997, extreme
cold killed twice as many Americans as heat waves, according to the
U.S. Department of the Interior.
15
It is estimated that by 2050, global
warming will cause almost 400,000 more heat-related deaths each
year. But at the same time, 1.8 million fewer people will die from
cold.
16
As global temperatures increase, extremes of cold temperatures will
be mitigated in two ways: global warming will increase maximum
summer temperatures modestly and raise winter minimum temperatures
signifi cantly. Both factors should help reduce human death rates. An
increase in average temperature should be a cause for rejoicing among
the elderly, the infi rm, and babies, the population subgroups most sensi-
tive to extreme temperatures.
Changes in Precipitation
As the air temperature increases, evaporation from the oceans also
increases, which leads to increased humidity and increased global pre-
cipitation. And because moisture in the air is the major absorber of
the heat radiated from the earth's surface (more than half), a major
positive feedback loop exists. Rising temperatures increase the amount
of water vapor in the air, and the increased amount of water vapor
increases the temperature still further. Data from more than 5,000
rain gauges on six continents indicate that average annual rainfall has
increased by almost 1 inch during the past hundred years. Changes
in the ratio of rainfall to snowfall have also been detected. Since the
1960s, the earth's snow cover has decreased by about 10 percent, and
the thickness of the Antarctic ice cap has decreased by an astonishing
42 percent.
However, the increase in precipitation is not uniform over the globe.
Over North America, the increase in precipitation has been more than
an inch and a half, but wide variations exist among regions (fi gure 9.3).
The rule of thumb is that wet places will become wetter and dry places
will become drier. California, where the warm climate and irrigation
with subsurface waters have made the state the heart of America's veg-
etable farming, was hit particularly hard by declining precipitation
during the twentieth century, while the vast Midcontinental grain belt
has seen substantial increases. The reason for these aerial variations is
unknown.
