Climate Sensitivity Uncertainty: When is Good News Bad?

30 Pages Posted: 2 Feb 2015 Last revised: 10 Feb 2015

See all articles by Mark Freeman

Mark Freeman

Loughborough University

Gernot Wagner

New York University (NYU) - Department of Environmental Studies; New York University (NYU) - Robert F. Wagner Graduate School of Public Service

Richard J. Zeckhauser

Harvard University - Harvard Kennedy School (HKS); National Bureau of Economic Research (NBER)

Date Written: January 2015

Abstract

Climate change is real and dangerous. Exactly how bad it will get, however, is uncertain. Uncertainty is particularly relevant for estimates of one of the key parameters: equilibrium climate sensitivity—how eventual temperatures will react as atmospheric carbon dioxide concentrations double. Despite significant advances in climate science and increased confidence in the accuracy of the range itself, the “likely” range has been 1.5-4.5°C for over three decades. In 2007, the Intergovernmental Panel on Climate Change (IPCC) narrowed it to 2-4.5°C, only to reverse its decision in 2013, reinstating the prior range. In addition, the 2013 IPCC report removed prior mention of 3°C as the “best estimate.”We interpret the implications of the 2013 IPCC decision to lower the bottom of the range and excise a best estimate. Intuitively, it might seem that a lower bottom would be good news. Here we ask: When might apparently good news about climate sensitivity in fact be bad news? The lowered bottom value also implies higher uncertainty about the temperature increase, a definite bad. Under reasonable assumptions, both the lowering of the lower bound and the removal of the “best estimate” may well be bad news.

Suggested Citation

Freeman, Mark and Wagner, Gernot and Zeckhauser, Richard J., Climate Sensitivity Uncertainty: When is Good News Bad? (January 2015). NBER Working Paper No. w20900, Available at SSRN: https://ssrn.com/abstract=2558952

Mark Freeman (Contact Author)

Loughborough University ( email )

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Gernot Wagner

New York University (NYU) - Department of Environmental Studies ( email )

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New York University (NYU) - Robert F. Wagner Graduate School of Public Service ( email )

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Richard J. Zeckhauser

Harvard University - Harvard Kennedy School (HKS) ( email )

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National Bureau of Economic Research (NBER) ( email )

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