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Forecast
for future:
Deluge and drought
NY Times - 8/29
It has been a
summer of extremes. Rains have deluged Europe and Asia, swamping
cities and villages and killing some 2,000 people, while drought
and heat have seared the American West and Eastern cities. What is
going on?
The floods and
droughts could simply be flickers in the inherently chaotic
weather system, some experts say. But many warn that such extremes
will be increasingly common as the world grows warmer.
Such a shift
could pose big problems in places where water is already a
strained resource, they say.
"Their water
use is already finely balanced, and based on hydrology they think
they're going to get, and climate change is telling us they're
going to get something different," said Dr. Peter H. Gleick,
the director of the Pacific Institute, a private environmental
research center in Oakland, Calif.
A warmer world is
more likely to be a wetter one, experts warn, with more
evaporation resulting in more rain, in heavy and destructive
downpours.
But in a
troublesome twist, that world may also include more intense
droughts, as the increased evaporation parches soils between
occasional storms.
"In a hotter
climate, your chances of being caught with either too much or too
little are higher," said Dr. John M. Wallace, a professor of
atmospheric sciences at the University of Washington.
And the globe is
getting warmer. The last several decades of global temperature
readings curve up sharply on graphs.
Climate experts
concluded for the first time last year that humans were causing
most of the warming trend by burning coal and oil, which release
carbon dioxide and other heat-trapping greenhouse gases.
The main way that
warming is likely to manifest itself, scientists say, is through
changes in the balance of water as liquid, vapor and ice.
Still, a
scientific debate persists. Some experts say the earth has
built-in buffering mechanisms that can limit extremes. But many
others say that past records, current trends and computer models
all point to big changes ahead. One new study this summer found
evidence that the Asian monsoon, as part of the warming trend, has
already intensified.
Generally,
agriculture is expected to falter in arid subtropical areas like
the eastern Mediterranean and southern Africa, while flourishing
in northern climes — like the North American wheat belt — as
more precipitation and longer growing seasons boost yields.
But climate
experts say that even there, rain is more likely to fall as
field-scouring torrents. Government scientists have already
measured a significant rise in downpour-style storms in the United
States over the last 100 years.
Long-term
planners in the western United States are already trying to
adjust. Next year, California will for the first time incorporate
climate change into its five-year water-management plan.
Water supplies
there are already squeezed by growing populations, said Jonas
Minton, the deputy director of the California Department of Water
Resources. A warming climate is intensifying the problem, he said.
Over the past 50
years, he said, winter precipitation in the Sierra Nevadas has
been falling more and more in the form of rain, increasing flood
risks, instead of as snow, which supplies farmers and taps alike
as it melts in the spring.
One of the
clearest climate shifts can be seen in mountain glaciers, said Dr.
Lonnie G. Thompson, the director of the Byrd Polar Research Center
at Ohio State University.
Some glaciers,
like those in the Alps, were already retreating before the
20th-century burst of greenhouse emissions. But the rate of
melting in the last decade in Peru, Tibet and many other places
has quickened far beyond the pre-industrial pace, he said.
Referring to the
glaciers, Dr. Thompson said: "It doesn't matter if you're in
the Himalayas, South America, Africa. They are all speaking with
the same voice. The system is changing."
The shriveling of
mountain glaciers is likely to eventually disrupt water and
hydroelectric power from Cuzco, Peru, to New Delhi, even as
populations in such cities continue to grow.
In the short run,
the melting could unleash sudden floods and avalanches as it
overwhelms reservoirs and stream beds, experts say.
The United
Nations Environment Program recently identified 44 glacier-fed
lakes in Bhutan and Nepal that are swelling rapidly and could pose
a risk of disastrous flash floods this decade.
In the long run,
though, these long-frozen sources of water will run dry, said
Cesar Portocarrero, a Peruvian engineer who worked for Electroperu,
the government-owned power company, for 25 years monitoring the
country's glacial water supply. He now serves as a consultant to
Dr. Thompson.
Mr. Portocarrero
said some Peruvian planners had explored the notion of supplying
the thirsty cities along the Pacific coast with water from the
Amazon River basin by building pipelines through the Andes. The
costs of such a project would be enormous, he said.
In the meantime,
the shifting climate is reflected in other ways in his hometown,
Huaraz, a small city perched 10,000 feet up the Andes.
"I was doing
work in my house the other day and saw mosquitoes," Mr.
Portocarrero said. "Mosquitoes at more than 3,000 meters. I
never saw that before. It means really we have here the evidence
and consequences of global warming."
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