Klimaatverandering 117

'Climate Change's Uncertainty Principle

Scientists say they can never be sure exactly how
extreme global warming might become, but that's no
excuse for delaying action

By David Biello <

The Intergovernmental Panel on Climate Change in its
first report in 1990 predicted that temperatures would
warm by 0.5 degree Fahrenheit (0.3 degree Celsius) per
decade if no efforts were made to restrain greenhouse
gas emissions. But the panel of scientists and other
experts was wrong: By 2001, the group estimated that
average temperatures would increase by 2.7 to 8.1
degrees F (1.5 to 4.5 degrees C) in the 21st century,
and they raised the lower end to 3.6 degrees F (2
degrees C) this year in their most recent report. In
essence, neither this international team of experts nor
any other can say with any certainty just how bad global warming may get.

There is a simple explanation for this, says atmospheric physicist Gerard Roe of the University of Washington
(U.W.) in Seattle: Earth's climate is extremely
sensitive. In other words, small changes in various
physical processes that control climate lead to big
results. "If nothing else changed by [warming], a
doubling of carbon dioxide would ultimately lead to a temperature change of about 1.2 [degrees] C," [(2.1 degrees F)] Roe says. "In fact, because of internal processes within the climate system, such as changing snow cover, clouds and water vapor in the atmosphere, our best estimate is that the actual warming would be two to four times larger than that."

Some of these feedback processes are poorly understood--
like how climate change affects clouds--and many are
difficult to model, therefore the climate's propensity
to amplify any small change makes predicting how much
and how fast the climate will change inherently
difficult. "Uncertainty and sensitivity are inextricably linked," Roe says. "Some warming is a virtual certainty, but the amount of that warming is much less certain."'

Lees verder: http://www.sciam.com/article.cfm?articleID=D979C4C5-E7F2-99DF-36EBE57F2339C2C1&sc=I100322