[env-trinity] FW: More Bad News for Arid West
sari at sisqtel.net
Mon Apr 9 14:50:12 PDT 2007
>Permanent drought predicted for Southwest; Study says global warming
>threatens to create a Dust Bowl-like period. Water politics could also get
>Los Angeles Times - 4/6/07
>By Alan Zarembo and Bettina Boxall, staff writers
>The driest periods of the last century - the Dust Bowl of the 1930s and the
>droughts of the 1950s - may become the norm in the Southwest United States
>within decades because of global warming, according to a study released
>The research suggests that the transformation may already be underway. Much
>of the region has been in a severe drought since 2000, which the study's
>analysis of computer climate models shows as the beginning of a long dry
>The study, published online in the journal Science, predicted a permanent
>drought by 2050 throughout the Southwest - one of the fastest-growing
>regions in the nation.
>The data tell "a story which is pretty darn scary and very strong," said
>Jonathan Overpeck, a climate researcher at the University of Arizona who was
>not involved in the study.
>Richard Seager, a research scientist at Lamont-Doherty Earth Observatory at
>Columbia University and the lead author of the study, said the changes would
>force an adjustment to the social and economic order from Colorado to
>"There are going to be some tough decisions on how to allocate water," he
>said. "Is it going to be the cities, or is it going to be agriculture?"
>Seager said the projections, based on 19 computer models, showed a
>surprising level of agreement. "There is only one model that does not have a
>drying trend," he said.
>Philip Mote, an atmospheric scientist at the University of Washington who
>was not involved in the study, added, "There is a convergence of the models
>that is very strong and very worrisome."
>The future effect of global warming is the subject of a United Nations
>report to be released today in Brussels, the second of four installments
>being unveiled this year.
>The first report from the Intergovernmental Panel on Climate Change was
>released in February. It declared that global warming had become a "runaway
>train" and that human activities were "very likely" to blame.
>The landmark report helped shift the long and rancorous political debate
>over climate change from whether man-made warming was real to what could be
>done about it.
>The mechanics and patterns of drought in the Southwest have been the focus
>of increased scrutiny in recent years.
>During the last period of significant, prolonged drought - the Medieval
>Climate Optimum from about the years 900 to 1300 - the region experienced
>dry periods that lasted as long as 20 years, scientists say.
>Drought research has largely focused on the workings of air currents that
>arise from variations in sea-surface temperature in the Pacific Ocean known
>as El Niño and La Niña.
>The most significant in terms of drought is La Niña. During La Niña years,
>precipitation belts shift north, parching the Southwest.
>The latest study investigated the possibility of a broader, global climatic
>mechanism that could cause drought. Specifically, they looked at the Hadley
>cell, one of the planet's most powerful atmospheric circulation patterns,
>driving weather in the tropics and subtropics.
>Within the cell, air rises at the equator, moves toward the poles and
>descends over the subtropics.
>Increasing levels of greenhouse gases, the researchers said, warms the
>atmosphere, which expands the poleward reach of the Hadley cell. Dry air,
>which suppresses precipitation, then descends over a wider expanse of the
>Mediterranean region, the Middle East and North America.
>All of those areas would be similarly affected, though the study examined
>only the effect on North America in a swath reaching from Kansas to
>California and south into Mexico.
>The researchers tested a "middle of the road" scenario of future carbon
>dioxide emissions to predict rainfall and evaporation. They assumed that
>emissions would rise until 2050 and then decline. The carbon dioxide
>concentration in the atmosphere would be 720 parts per million in 2100,
>compared with about 380 parts per million today.
>The computer models, on average, found about a 15% decline in surface
>moisture - which is calculated by subtracting evaporation from precipitation
>- from 2021 to 2040, as compared with the average from 1950 to 2000.
>A 15% drop led to the conditions that caused the Dust Bowl in the Great
>Plains and the northern Rockies during the 1930s.
>Even without the circulation changes, global warming intensifies existing
>patterns of vapor transport, causing dry areas to get drier and wet areas to
>get wetter. When it rains, it is likely to rain harder, but scientists said
>that was unlikely to make up for losses from a shifting climate.
>Kelly Redmond, deputy director of the Western Regional Climate Center in
>Reno, who was not involved in the study, said he thought the region would
>still have periodic wet years that were part of the natural climate
>But, he added, "In the future we may see fewer such very wet years."
>Although the computer models show the drying has already started, they are
>not accurate enough to know whether the drought is the result of global
>warming or a natural variation.
>"It's really hard to tell," said Connie Woodhouse, a paleoclimatologist at
>the University of Arizona. "It may well be one of the first events we can
>attribute to global warming."
>The U.S. and southern Europe will be better prepared to deal with frequent
>drought than most African nations.
>For the U.S., the biggest problem would be water shortages. The seven
>Colorado River Basin states - Colorado, Wyoming, Utah, Nevada, New Mexico,
>Arizona and California - would battle each other for diminished river flows.
>Mexico, which has a share of the Colorado River under a 1944 treaty and has
>complained of U.S. diversions in the past, would join the struggle.
>Inevitably, water would be reallocated from agriculture, which uses most of
>the West's supply, to urban users, drying up farms. California would come
>under pressure to build desalination plants on the coast, despite
>"This is a situation that is going to cause water wars," said Kevin
>Trenberth, a scientist at the National Center for Atmospheric Research in
>"If there's not enough water to meet everybody's allocation, how do you
>divide it up?"
>Officials from seven states recently forged an agreement on the current
>drought, which has left the Colorado River's big reservoirs - Lake Powell
>and Lake Mead - about half-empty. Without some very wet years, federal water
>managers say, Lake Mead may never refill.
>In the next couple of years, water deliveries may have to be reduced to
>Arizona and Nevada, whose water rights are second to California. #
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