melting of the world’s glaciers, resulting in a loss of fresh-water
supplies, especially in South Asia, China, and South America;
melting of the Greenland and Antarctic ice caps, resulting in rising
sea levels and the likely displacement of tens of millions of people
from their current homes (especially in the low island states of the
developing world);
a reduction of animal habitat and the extinction of some species,
leading to a reduction in biodiversity;
reduced crop yields (especially in Africa and parts of Asia), resulting
in reduced food supplies in regions already facing hunger problems;
and
rising intensity of storms and increasing volatility of weather patterns.The costs associated with these changes are easy to imagine but difficult
to quantify precisely. Current estimates of the effects of climate change,
expressed in terms of a permanent reduction in world GDP, range from 3
percent to 20 percent. The width of this range indicates just how much
uncertainty and debate continues to exist about the effects of global
climate change, but even the lower bound of this range—an annual global
cost of U.S.$1.2 trillion forever—represents an enormous sum. Even
worse, these costs will probably be unevenly distributed across the
world’s population; the developing world is likely to bear the lion’s share
of the burden of global climate change.
In summary, the atmospheric concentration of greenhouse gases is
already 40 percent above its pre-industrial levels, and some climate
change is already occurring. But if the global climate is to be stabilized in