Possible Global Warming Estimates Double - Potential 11C Increase

[hatrack]

"Since 1991, the UN Intergovernmental Panel on Climate Change (IPCC) report has predicted a 1.5–4.5 °C increase in average temperatures due to a doubling of CO2 levels. Now, new results from distributive computing projects suggest that the temperature increase could go as high as 11 °C. Although the IPCC has been reluctant to embrace these estimates, some scientists say that new developments make the wider temperature range nearly impossible for the panel to ignore.

“Our experiment shows that increased levels of greenhouse gases could have a much greater impact on climate than previously thought,” says David Stainforth, a climate scientist at Oxford University. He and his colleagues at Climateprediction.net (www.climateprediction.net), a collaborative effort of British universities and government agencies, will be discussing their results at the European Geosciences Union meeting in April. The researchers enlisted 95,000 people from 150 countries to download a general circulation model (GCM) and run it using the idle processing capacity on their personal computers. The distributed computing project enabled the researchers to run thousands of versions of the model, in which 21 parameters were set to alternative values considered plausible by experts (Nature 2005, 433, 403–406).

Stainforth and his associates analyzed more than 2000 of the simulations that perturbed 6 parameters, such as the threshold of relative humidity, the cloud-to-rain conversion rate, and the ice fall speed. When CO2 concentration doubles from pre-industrial levels—as is expected to happen by about 2050—the simulations predict that global mean temperature could rise over a period of many years anywhere from 1.9 to 11.5 °C. “An important message is that we didn’t get any measures of climate sensitivity less than 1.9 °C,” Stainforth says. This means that policy makers can be increasingly confident that global temperature will rise by no less than 2 °C in response to doubling CO2 levels. But it is also possible that temperatures could rise by as much as 11 °C, Stainforth cautions.

The Climateprediction.net experiment is the first time that a GCM has produced climate responses substantially greater than 5 °C, says Michael Schlesinger, a climate scientist at the University of Illinois at Urbana–Champaign. “When the IPCC set the climate sensitivity range at 1.5–4.5 °C in 1990, it had a strong constraint on what science could do,” says Schlesinger, who helped write the first IPCC report that set the range. “If climate modelers, myself included, got a value higher than 4.5, they changed the model to make it otherwise,” he says. That action, Schlesinger says, was driven in part because climatologists did not want to provide fuel for climate change skeptics to argue that large ranges of uncertainty in model outcomes undermine any rationale for taking action on greenhouse gas emissions."

EDIT

http://pubs.acs.org/subscribe/journals/esthag-w/2005/mar/science/jp_greenhouse.html

[Viking12]

1. Uncertainty can go either way.

When someone tries to dismiss the threat of global warming by citing the uncertainty margins, remind them that uncertainty may also suggest a much greater deltaT.

[papau]

2. Last ice age was a 2 degree job - so low end 1.9 degrees is scary.

:-(

[phantom power]

3. That's an appalling number.

Even half of that would represent a climate effectively alien to the current ecologies.

[Wilms]

4. Thanks, Hatrack. Sort of n/t