[tt] [x-risk] CO2 effects will persist for 1000 years

[Hughes, James J.]

http://www.washingtonpost.com/wp-dyn/content/article/2009/01/26/AR200901
2602037_pf.html

Long Droughts, Rising Seas Predicted Despite Future CO2 Curbs

By Juliet Eilperin

Washington Post Staff Writer

Tuesday, January 27, 2009; A04

Greenhouse gas levels currently expected by mid-century will produce
devastating long-term droughts and a sea-level rise that will persist
for 1,000 years regardless of how well the world curbs future emissions
of carbon dioxide, an international team of scientists reported
yesterday.

Top climate researchers from the U.S. National Oceanic and Atmospheric
Administration, Switzerland and France said their analysis shows that
carbon dioxide will remain near peak levels in the atmosphere far longer
than other greenhouse gases, which dissipate relatively quickly.

"I think you have to think about this stuff as more like nuclear waste
than acid rain: The more we add, the worse off we'll be," NOAA senior
scientist Susan Solomon told reporters in a conference call. "The more
time that we take to make decisions about carbon dioxide, the more
irreversible climate change we'll be locked into."

At the moment, carbon concentrations in the atmosphere stand at 385
parts per million. Many climate scientists and the United Nations'
Intergovernmental Panel on Climate Change have set a goal of stabilizing
atmospheric carbon at 450 ppm, but current projections put the world on
track to hit 550 ppm by 2035, rising after that point by 4.5 percent a
year.

The new study, published in the Proceedings of the National Academy of
Sciences, projects that if carbon dioxide concentrations peak at 600
ppm, several regions of the world -- including southwestern North
America, the Mediterranean and southern Africa -- will face major
droughts as bad or worse than the Dust Bowl of the 1930s. Global sea
levels will rise by about three feet by the year 3000, a projection that
does not factor in melting glaciers and polar ice sheets that would
probably result in significant additional sea level rises.

Even if the world managed to halt the carbon dioxide buildup at 450 ppm,
the researchers concluded, the subtropics would experience a 10 percent
decrease in precipitation, compared with the 15 percent decrease they
would see at 600 ppm. That level is still akin to mega-droughts such as
the Dust Bowl. The already parched U.S. Southwest would probably see a 5
percent drop in precipitation during its dry season.

Mary-Elena Carr, associate director of the Columbia Climate Center,
called the new projections "very sobering." She noted that while
societies can try to adapt to reduced precipitation with better farming
techniques and other measures, there is a limit to the ability to cope
with severe drought.
"When it's drought, that is hard, because we have a finite amount of
water and a growing population we need to feed," Carr said, adding that
the severe storm surges associated with higher sea levels also pose a
dangerous challenge to large populations.

The rising sea levels anticipated under a conservative projection, the
authors wrote, would cause "irreversible commitments to future changes
in the geography of the Earth, since many coastal and island features
would ultimately become submerged."

The scientists noted that the world's oceans are already absorbing an
enormous amount of carbon, but over time this will reach a limit and
they will no longer absorb as much. As this happens, the atmospheric
temperature will remain nearly constant.

Most previous scientific analyses, including the U.N. panel's summary
report for policymakers, have assessed climate change impacts on a
100-year time scale. A few researchers, such as Ken Caldeira of the
Carnegie Institution's Department of Global Ecology, have argued that it
makes more sense to look at a time scale of at least 500 years.

In an e-mail yesterday, Caldeira wrote that he had debated this point
with other contributors to the U.N. reports in 2001, adding, "If you
took our long term climate commitment seriously, you would not use
100-year [global warming projections] to compare effects of different
gases."

Carbon dioxide emissions account only for about half of human-induced
global warming, but the several other gases that play a role, including
methane, dissipate more quickly. Solomon said policymakers could take
this into account when deciding how best to reduce greenhouse gases
overall.

"We ought to be extra careful about how much carbon dioxide we put out
in the future," she said, adding that politicians often focus on the
less certain but potentially disastrous impacts of climate change but
would do well to focus on the more predictable consequences. "The parts
that we don't know, that are possible but very uncertain, shouldn't get
in the way of what we do know."

A separate study in the same journal yesterday suggests that the iconic
emperor penguins of the Antarctic could be headed to extinction by 2100
if the sea ice shrinks by the predicted amounts. That paper -- written
by scientists from the Woods Hole Oceanographic Institution, National
Center for Atmospheric Research, the National Snow and Ice Data Center
in Boulder, Colo., and France's Centre National de la Recherche
Scientifique -- projects that the number of breeding pairs in a colony
in Terre Adelie, Antarctica, will decline from about 6,000 to 400 by the
end of the century because the animals depend on sea ice for breeding,
foraging and molting habitat.

Emperor penguins would have to migrate or change the timing of their
growth stages to avoid extinction, the authors write, but "evolution or
migration seem unlikely for such long-lived species at the remote
southern end of the Earth."



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