Page 380 - Earth's Climate Past and Future

356 PART V • Historical and Future Climate Change

In built-up coastal regions such as the East Coast and efforts. This subject is no longer entirely taboo, how-
coast of the Gulf of Mexico in the United States, ever- ever, because the scope of what we have already done to
greater engineering efforts (construction of sea walls and past climate and will do to future climate has become
pumping of sand to replenish beaches) will become nec- clearer.
essary unless communities decide to retreat from vulner- Humans face an interesting dilemma suggested by
able regions. Insurance companies have already begun to the imaginary sequence in Figure 19–15. If all our emis-
increase premiums sharply for homes and buildings in sions of sulfate and carbon aerosols were suddenly elim-
such areas. Some scientists have recently suggested that inated, precipitation would wash the excess aerosols out
the intensity of the largest hurricanes will increase with of the lower atmosphere within a few weeks, and their
global warming, but this prediction has been challenged. cooling effect would quickly disappear. As a result of an
Perhaps the greatest “wild card” in assessing the cli- attempt to clean up our aerosol emissions, the climate
matic future is the possibility that warming will push system would register a large short-term warming.
the Greenland ice sheet into a regime of irreversible In contrast, a simultaneously abrupt and total end to
melting. Although this possibility is still a minority global CO emissions by humans would lead to a much
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opinion among climate scientists, it is no longer consid- slower reduction in atmospheric CO levels. The ocean
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ered impossible. If the entire Greenland ice sheet were would take up one-half of the pulse of excess CO pro-
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to melt over future centuries (or millennia?), the 6-m duced by previous human activities within 50 years, but
(20-ft) rise in sea level would be a true catastrophe for 10% of the total would remain in the atmosphere for
billions of people living along the world’s coasts. People
in flat rural areas would have to retreat inland many
miles as the sea invaded. The fate of most of the great
cities of the world is harder to predict. Each of them Higher CO and SO 2
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would have to decide whether or not it would make
sense to build massive walls as armor against such a
large rise in sea level.
Some of the largest changes caused by future global
warming may have relatively little broad economic
impact on humans and yet still be crucial from an
ecosystem perspective. Large-scale melting of sea ice 0
and permafrost and loss of tundra around the Arctic Excess input rates
margins will hardly be a central issue in the lives of peo-
ple who have never traveled to that barren land. But the Higher CO 2
shrinking of those habitats could devastate caribou,
polar bears, and the rest of the polar ecosystem, includ-
ing the cultures of the few native people who still rely
on hunting of polar-adapted animals for survival. Loss
of species in other regions because of rapid northward
or upward dislocation of preferred environments could Sulfate
also be large. 0
Acidification of the oceans will proceed as long as Excess concentrations in atmosphere
we keep burning carbon, and it will occur whether we
burn it slowly (using conservation measures) or quickly
(the “business as usual” approach). By the year 2300, the
oceans may become so close to acidic that one of the
major planktic organisms (coccoliths; see Chapter 2)
may no longer be able to form CaCO shells. If this Warmer
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happens, further transformations of the entire chem-
istry of the ocean could occur. Years Hundreds of years
Global temperature change
Time
Climate Modification?
FIGURE 19-15 What if we abruptly ended CO and SO 2
2
Until recently, the possibility of altering Earth’s future emissions? If humans instantly eliminated all industrial and
climate by engineering was rarely discussed among other emissions of greenhouse gases and SO , the sulfates and
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mainstream scientists, many of whom feel that we their cooling effect would soon disappear, but the CO and its
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should minimize future CO increases by conservation warming effect would linger for centuries.
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