Science: Climate Sensitivity May Be Slightly Less Than Thought

Earth's climate will warm in response to a doubling of atmospheric carbon dioxide compared to pre-industrial levels, but this increase may be slightly smaller than previous studies have estimated, researchers say.

This amount of warming, which refers specifically to global average surface air temperature, is called Earth's climate sensitivity. Researchers need a better handle on this number in order to better assess the impacts of future climate change.

Previous studies have suggested 3 degrees Kelvin as the best estimate of climate sensitivity, within a likely range of 2 to 4.5 degrees Kelvin. These estimates include some possibility that climate sensitivity could be much greater, which could lead to catastrophic climate changes in the coming decades.

The new research, conducted by Andreas Schmittner of Oregon State University and colleagues, suggests that the median sensitivity is 2.3 degrees Kelvin, within a likely range of 1.7 to 2.6 degrees Kelvin, and with very little chance that temperatures would increase much more than that. Their findings on Earth’s current climate sensitivity are based on temperature reconstructions of the Last Glacial Maximum, roughly 20,000 years ago, in combination with global climate models.

The research was published online in the 24 November edition of ScienceExpress.

“Many previous climate sensitivity studies have looked at the past only from 1850 through today, and not fully integrated paleoclimate data, especially on a global scale,” said Schmittner. “When you reconstruct sea and land surface temperatures from the peak of the last Ice Age 21,000 years ago—which is referred to as the Last Glacial Maximum—and compare it with climate model simulations of that period, you get a much different picture.

“If these paleoclimatic constraints apply to the future, as predicted by our model, the results imply less probability of extreme climatic change than previously thought,” he said.

While the new estimate is slightly smaller than previous estimates, even an increase in global air temperatures of just 2 degrees Kelvin would nonetheless have an important impact on global climate. The authors say their study demonstrates that paleoclimate data can be useful in reducing the uncertainty of future climate projections.

Kathy Wren

28 November 2011