Like It Or Not, Uncertainty And Climate Change Go Hand-In-Hand
While the new equation will help scientists quickly see the most likely
impacts, it also shows that far more extreme temperature changes - perhaps
15 degrees or more in the global mean - are possible, though not probable.
That same result also was reported in previous studies that used thousands
of computer simulations, and the new equation shows the extreme
possibilities are fundamental to the nature of the climate system. Much will
depend on what happens to emissions of carbon dioxide and other greenhouse
gases in the future. Since they can remain in the atmosphere for decades,
even a slight decrease in emissions is unlikely to do more than stabilize
overall concentrations, Roe said.
By: Staff Writers
Source: Tacoma WA (SPX), Terra Daily
URL:
http://www.terradaily.com/reports/Like_It_Or_Not_Uncertainty_And_Climate_Change_Go_Hand_In_Hand_999.html
Date: 26 October 2007
Despite decades of ever more-exacting science projecting Earth's warming
climate, there remains large uncertainty about just how much warming will
actually occur. Two University of Washington scientists believe the
uncertainty remains so high because the climate system itself is very
sensitive to a variety of factors, such as increased greenhouse gases or a
higher concentration of atmospheric particles that reflect sunlight back
into space.
In essence, the scientists found that the more likely it is that conditions
will cause climate to warm, the more uncertainty exists about how much
warming there will be.
"Uncertainty and sensitivity have to go hand in hand. They're inextricable,"
said Gerard Roe, a UW associate professor of Earth and space sciences.
"We're used to systems in which reducing the uncertainty in the physics
means reducing the uncertainty in the response by about the same proportion.
But that's not how climate change works."
Roe and Marcia Baker, a UW professor emeritus of Earth and space sciences
and of atmospheric sciences, have devised and tested a theory they believe
can help climate modelers and observers understand the range of
probabilities from various factors, or feedbacks, involved in climate
change. The theory is contained in a paper published in the Oct. 26 edition
of Science.
In political polling, as the same questions are asked of more and more
people the uncertainty, expressed as margin of error, declines substantially
and the poll becomes a clearer snapshot of public opinion at that time. But
it turns out that with climate, additional research does not substantially
reduce the uncertainty.
The equation devised by Roe and Baker helps modelers understand built-in
uncertainties so that the researchers can get meaningful results after
running a climate model just a few times, rather than having to run it
several thousand times and adjust various climate factors each time.
"It's a yardstick against which one can test climate models," Roe said.
Scientists have projected that simply doubling carbon dioxide in the
atmosphere from pre-Industrial Revolution levels would increase global mean
temperature by about 2.2 degrees Fahrenheit. However, that projection does
not take into account climate feedbacks - physical processes in the climate
system that amplify or subdue the response. Those feedbacks would raise
temperature even more, as much as another 5 degrees F according to the most
likely projection. One example of a feedback is that a warmer atmosphere
holds more water vapor, which in itself is a greenhouse gas. The increased
water vapor then amplifies the effect on temperature caused by the original
increase in carbon dioxide.
"Sensitivity to carbon dioxide concentration is just one measure of climate
change, but it is the standard measure," Roe said.
Before the Industrial Revolution began in the late 1700s, atmospheric carbon
dioxide was at a concentration of about 280 parts per million. Today it is
about 380 parts per million and estimates are that it will reach 560 to
1,000 parts per million by the end of the century.
The question is what all that added carbon dioxide will do to the planet's
temperature. The new equation can help provide an answer, since it links the
probability of warming with uncertainty about the physical processes that
affect how much warming will occur, Roe said.
"The kicker is that small uncertainties in the physical processes are
amplified into large uncertainties in the climate response, and there is
nothing we can do about that," he said.
While the new equation will help scientists quickly see the most likely
impacts, it also shows that far more extreme temperature changes - perhaps
15 degrees or more in the global mean - are possible, though not probable.
That same result also was reported in previous studies that used thousands
of computer simulations, and the new equation shows the extreme
possibilities are fundamental to the nature of the climate system.
Much will depend on what happens to emissions of carbon dioxide and other
greenhouse gases in the future. Since they can remain in the atmosphere for
decades, even a slight decrease in emissions is unlikely to do more than
stabilize overall concentrations, Roe said.
"If all we do is stabilize concentrations, then we will still be risking the
highest temperature change shown in the models," he said.
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