Researchers tapping the computer power of 26,000 idling personal computers say that, in the coming century, greenhouse gasses could make Earth even hotter than current theories predict. The findings shake up what had seemed to be an emerging consensus about global warming, although some balk at such an extreme perspective.
Last summer, a gathering of climate modelers, paleoclimatologists, and other climate researchers were converging on a middle ground (Science, 13 August 2004, p. 932). Three kinds of climate studies suggested that a doubling of greenhouse gasses would warm Earth in the next couple of centuries somewhere between 2°C and 4°C. One of the studies, conducted by James Murphy of the Hadley Center for Climate Prediction and Research in Exeter, U.K., and colleagues involved altering 29 climate model variables that control physical properties such as the behavior of clouds, atmospheric convection, and winds. Given their available computing resources, they could perturb only one parameter at a time for a total of 53 simulations.
Now modeler David Stainforth of the University of Oxford, U.K., and 15 colleagues have pumped-up this approach by utilizing the processing capacity of 26,000 personal computers. Volunteers from the general public contributed the power of their machines to climateprediction.net, allowing the researchers to vary six parameters, several at one time for a whopping 2578 simulations. Most of the simulations predicted a global temperature rise of around 3.4°C, but some ran as hot as 11°C, 2°C warmer than any kind of study before it. Stainforth, whose group publishes its work in the 27 January issue of Nature, says he can't say how likely the 11°C heat-up is because "we can't yet give a probability for our results."
Some experts have a gut reaction. "I just can't believe climate sensitivity is 10°C," says paleoclimatologist Thomas Crowley of Duke University in Durham, North Carolina. Climate's responses to past, natural changes in greenhouse gases or equivalent climate drivers, such as volcanic eruptions, have just been too modest for that, he says. Until modelers can rein in their unruly simulations—perhaps using the tens of thousands of additional simulations now in hand at climateprediction.net Crowley says he will stick with a moderately strong warming.