Are scientists underestimating earth's sensitivity to CO2?

Scientific Blogging: A study appearing in Nature Geoscience this week claims that Earth's temperature may be 30-50% more sensitive to atmospheric carbon dioxide than previous estimates suggest, and the effects of this increased sensitivity could make climate change an even bigger threat than it already is.

The results of the study show that the models currently used to forecast climate change often neglect components of the Earth's climate system that vary over long timescales and have an important effect on temperature sensitivity--such as land-ice and vegetation.

The researchers compared results from a global climate model to temperature reconstructions of the Earth's environment three million years ago when global temperatures and carbon dioxide concentrations were relatively high. The temperature reconstructions were derived using data from three million-year-old sediments on the ocean floor.

"We found that, given the concentrations of carbon dioxide prevailing three million years ago, the model originally predicted a significantly smaller temperature increase than that indicated by the reconstructions. This led us to review what was missing from the model," said Daniel Lunt, one of the study's co-athors.

The authors argue that the increased temperatures indicated by the reconstructions can be explained if factors that vary over long timescales, such as land-ice and vegetation, are included in the model. This is primarily because changes in vegetation and ice lead to more sunlight being absorbed, which in turn increases warming.

Including these long-term processes in the model resulted in an increased temperature response of the Earth to carbon dioxide, indicating that the Earth's temperature is more sensitive to carbon dioxide than previously recognized. Climate models used by bodies such as the IPCC often do not fully include these long-term processes, thus these models do not entirely represent the sensitivity of the Earth's temperature to carbon dioxide…..

The earth seen from Apollo 17