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 New century of thirst for world's mountains
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Most detailed forecast to date shows sharp snowpack decline between now
and year 2100; New Zealand, Latin America, Western US, European ranges
hardest hit

RICHLAND, Wash. - By the century's end, the Andes in South America
will have less than half their current winter snowpack, mountain ranges
in Europe and the U.S. West will have lost nearly half of their
snow-bound water, and snow on New Zealand's picturesque snowcapped
peaks will all but have vanished.

Such is the dramatic forecast from a new, full-century model that
offers detail its authors call "an unprecedented picture of climate
change." The decline in winter snowpack means less spring and summer
runoff from snowmelt. That translates to unprecedented pressure on
people worldwide who depend on summertime melting of the winter
snowpack for irrigation and drinking water.

Hardest hit are mountains in temperate zones where temperatures remain
freezing only at increasingly higher elevations, said Steven J. Ghan,
staff scientist at the Department of Energy's Pacific Northwest
National Laboratory and lead author of a study describing the model in
the current Journal of Climate. PNNL scientist Timothy Shippert was
co-author.

Alaska in 2100 will maintain but 64 percent of its year 2000 snowpack.
In Europe, the Alps will be at 61 percent and Scandinavia 56 percent.
The Sierras, Cascades and southern Rockies will be at 57 percent of
current levels. The Andes will drop to 45. And Mt. Cook and its
snowcapped neighbors in New Zealand will be much less scenic at 16
percent of current.

Ghan said the model, which actually simulated years 1977 to 2100 to use
known data as calibration, differs from past attempts because it
generates snow information for small areas - 5 kilometer grids, or
about 3-miles - on mountains ranges over such a long period.

"Global climate models have never been run at 5 kilometers resolution
for a period covering more than a couple of months," Ghan said, "even
on the biggest computers in the world."

Ghan deployed a divide-and-conquer method to data crunching called
"physically-based global downscaling" he and colleagues had used
previously on mountains in the U.S. West. The world's mountain ranges
are chopped into 10 different "elevation classes." For each elevation
class, data such as air circulation, moisture and temperature is used
to determine snowfall to the surface. The surface snow is then
distributed across the grids according to the local surface elevation.

The entire century-plus simulation, based on the National Center for
Atmospheric Research Community Climate System Model funded by the
National Science Foundation and DOE, can be run on a modest
supercomputer over a few weeks. Ghan and Shippert used one at the
PNNL-based W.R. Wiley Environmental Molecular Sciences Laboratory.

Ghan cautioned about "significant limitations" to the model. For
example, field observations in Africa suggest the famous snows of Mt.
Kilimanjaro will be gone within decades, and on Greenland signs point
to accelerated snow and ice melt.

"This climate model doesn't show that," Ghan said. "That doesn't mean
Kilimanjaro and Greenland aren't in trouble. But our model doesn't
account for all of the snow loss that is possible. Our model neglects
downward flow of snow by avalanches and snow slides, glacial creep in
places where snowfall is heavy and the snow doesn't have time to melt."

(Source: DOE/Pacific Northwest National Laboratory)