[Marxism] Permanent drought predicted for Southwest USA

[Louis Proyect <lnp3@xxxxxxxxx>]

http://www.latimes.com/news/science/la-sci-swdrought6apr06,0,122112.story?coll=la-home-headlines

Permanent drought predicted for Southwest
Study says global warming threatens to create a 
Dust Bowl-like period. Water politics could also get heated.
By Alan Zarembo and Bettina Boxall
Times Staff Writers

April 6, 2007

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 Thursday.

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 period.

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 California.

"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 variation.

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 environmental concerns.

"This is a situation that is going to cause water 
wars," said Kevin Trenberth, a scientist at the 
National Center for Atmospheric Research in Boulder, Colo.

"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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