Expert judgments about transient climate response to alternative future trajectories of radiative forcing
Edited by Roger E. Kasperson, Clark University, Worcester, MA, and approved June 3, 2010 (received for review August 5, 2009)
Abstract
There is uncertainty about the response of the climate system to future trajectories of radiative forcing. To quantify this uncertainty we conducted face-to-face interviews with 14 leading climate scientists, using formal methods of expert elicitation. We structured the interviews around three scenarios of radiative forcing stabilizing at different levels. All experts ranked “cloud radiative feedbacks” as contributing most to their uncertainty about future global mean temperature change, irrespective of the specified level of radiative forcing. The experts disagreed about the relative contribution of other physical processes to their uncertainty about future temperature change. For a forcing trajectory that stabilized at 7 Wm-2 in 2200, 13 of the 14 experts judged the probability that the climate system would undergo, or be irrevocably committed to, a “basic state change” as ≥0.5. The width and median values of the probability distributions elicited from the different experts for future global mean temperature change under the specified forcing trajectories vary considerably. Even for a moderate increase in forcing by the year 2050, the medians of the elicited distributions of temperature change relative to 2000 range from 0.8–1.8 °C, and some of the interquartile ranges do not overlap. Ten of the 14 experts estimated that the probability that equilibrium climate sensitivity exceeds 4.5 °C is > 0.17, our interpretation of the upper limit of the “likely” range given by the Intergovernmental Panel on Climate Change. Finally, most experts anticipated that over the next 20 years research will be able to achieve only modest reductions in their degree of uncertainty.
Acknowledgments.
We thank the experts listed in Table 1 for their assistance in this project, as well as Peter Adams, Jay Apt, Kristian Dahl, Hadi Dowlatabadi, Ben Feltzer, Michael Mastrandrea, Jerry Melillo, Mitchell Small, Patricia Steranchak, and Larry Williams. The work was supported by a contract from the Electric Power Research Institute (PID 060968) and by the Climate Decision Making Center through a cooperative agreement between the US National Science Foundation (SES-0345798) and Carnegie Mellon University.
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Cover image: Pictured are small blood vessels that have formed in vitro from endothelial cells. A type of vascular abnormality known as cerebral cavernous malformation (CCM) has been linked to mutations in one of three genes that contribute to neurovascular development. Joycelyn W�stehube et al. show that CCM1 (also known as KRIT1) keeps the endothelium quiescent (blue cells compared to yellow control cells) by preventing uncontrolled angiogenesis, and that CCM1-silenced human endothelial cells recapitulate hallmark CCM vascular irregularities in mice. See the article by Wüstehube et al. on pages 12640–12645. Image courtesy of Arne Bartol and Joycelyn Wüstehube.
Submission history
Published online: June 28, 2010
Published in issue: July 13, 2010
Keywords
Acknowledgments
We thank the experts listed in Table 1 for their assistance in this project, as well as Peter Adams, Jay Apt, Kristian Dahl, Hadi Dowlatabadi, Ben Feltzer, Michael Mastrandrea, Jerry Melillo, Mitchell Small, Patricia Steranchak, and Larry Williams. The work was supported by a contract from the Electric Power Research Institute (PID 060968) and by the Climate Decision Making Center through a cooperative agreement between the US National Science Foundation (SES-0345798) and Carnegie Mellon University.
Notes
This article is a PNAS Direct Submission.
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Competing Interests
The authors declare no conflict of interest.
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