A survey of climate scientists reveals uncertainty in their predictions of changes to the global climate, yet finds that they believe there is a real chance of passing a “tipping point” that could result in large socio-economic impacts in the next two centuries. The expert elicitation was conducted between October 2005 and April 2006 with a computer-based interactive questionnaire completed individually by participants. A total of 52 experts participated in the elicitation (see Table S2 in the PDF below for names and affiliations). The questionnaire included 7 events of crossing a tipping point. Elmar Kriegler and colleagues asked the climate experts to estimate the likelihood of impacts to components of the climate system under different warming scenarios.
The five systems discussed in the paper concerned major changes in the North Atlantic Ocean circulation, the Greenland and Western Antarctic ice sheets, the Amazon rainforest, and El Niño. The probabilities given by the experts varied widely, but on average, they assigned significant chances to a tipping point in this or the next century for at least the medium to high warming scenarios.
Using the experts’ more conservative estimates, the authors calculate a 1 in 6 chance that a tipping event will occur if the temperature increase in the next 200 years is between 2 and 4 degrees Celsius. For a higher temperature increase, the probability was just over 1 in 2. According to the authors, the results suggest that the large uncertainties that come with climate predictions do not imply low probability that catastrophic events will occur.
Since the survey was conducted in 2005 and 2006, I wonder if the opinions are equivalent today. They might have gotten more bang for their buck if they’d used a survey company like Gallup. I’m sure the results would be faster.
The paper is titled: Imprecise probability assessment of tipping points in the climate system
Elmar Kriegler, Jim W. Hall, Hermann Held, Richard Dawson, and Hans Joachim Schellnhuber,
Potsdam Institute for Climate Impact Research, PO Box 60 12 03, 14412 Potsdam, Germany; Department of Engineering and Public Policy, Carnegie Mellon
University, Pittsburgh, PA 15213-3890; School of Civil Engineering and Geosciences, Newcastle University, Newcastle-upon-Tyne NE1 7RU, United Kingdom;
Tyndall Centre for Climate Change Research, United Kingdom; and eEnvironmental Change Institute, Oxford University, Oxford OX1 3QY, United Kingdom
Edited by William C. Clark, Harvard University, Cambridge, MA, and approved February 2, 2009 (received for review September 16, 2008)
Here is their diagram of the tipping possibilities in the global climate system:
Here is the PNAS abstract