Figure 17.39: The Boulder Glacier has melted back tremendously since 1985. Other moun-
tain glaciers around the world are also melting. ( 23 )
and stop them from colonizing many new areas. Parks and wildlife refuges might be left
protecting nothing. And biologists have already documented the extinction of high altitude
species that have nowhere higher to go.
Decreased snowpacks, shrinking glaciers, and the earlier arrival of spring will all lessen the
amount of water available in some regions of the world, including the western United States
and much of Asia. Ice will continue to melt and sea level is predicted to rise 18 to 97 cm
(7 to 38 inches) by 2100 (Figure17.40). An increase this large will gradually flood coastal
regions where about one-third of the world’s population lives, forcing billions of people to
move inland.
There will be more severe heat waves and heat-related illnesses and deaths. Drought could
make many marginal regions uninhabitable. Some modelers predict that the Midwestern
UnitedStateswillbecometoodrytosupportagricultureandtheareasthatcurrentlyproduce
our best agriculture would move into Canada. In all, about 10 to 50% of current cropland
worldwide may become unusable if CO 2 doubles.
Although scientists do not all agree, hurricanes are likely to become more severe and possibly
more frequent. Hurricanes cause a tremendous loss of life in developing nations and a loss of
property in developed ones. Tropical and subtropical insects will expand their ranges. This
will result in the spread of tropical diseases such as malaria, encephalitis, yellow fever, and
dengue fever.
You may notice that the numerical predictions above contain wide ranges. Sea level, for
example is expected to rise somewhere between 18 and 97 cm — quite a wide range. This