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Effects of CO2 May Be Underestimated In Climate Models

Research conducted by the University of Bristol, and the University of Leeds in the UK have demonstrated that our climate models may be underestimating the effects of CO2 on global temperatures.

In the long term, the Earth’s temperature may be 30-50 per cent more sensitive to atmospheric carbon dioxide

than has previously been estimated, reports a new study published in Nature Geoscience this week.

The results show that components of the Earth’s climate system that vary over long timescales — such as land-ice and vegetation — have an important effect on this temperature sensitivity, but these factors are often neglected in current climate models.

Dr Dan Lunt, from the University of Bristol, Alan Haywood, from the University of Leeds, and colleagues 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.

Lunt said, “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.”

The authors demonstrate 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 Intergovernmental Panel on Climate Change 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.

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Article appearing courtesy of ENN

[photo credit: PNNL – Pacific Northwest National Laboratory]