Better than even chance of major changes in global climate system, experts predict

Science Daily: An international team of researchers, led by Elmar Kriegler of the Potsdam Institute for Climate Impact Research (PIK), elicited the opinions of 52 climate scientists about the sensitivity of five so-called tipping elements. Tipping elements are parts of the climate system which, through human interference, can change quickly and irreversibly. In the current study, the sensitivity of the following tipping elements is evaluated: Atlantic thermohaline circulation, El Niño phenomenon, Amazon rainforest, Greenland, and West Antarctic ice sheets.

A total of 43 experts estimated upper and lower bounds for the probability of those elements undergoing dramatic changes, given three different global warming scenarios: a warming by less than 2°C, by 2 – 4°C, or by an extreme of 4 – 8°C until 2200. “Strong global warming of more than 4°C by the year 2200 so far does appear to be a clear possibility,” Kriegler says.

The analysis of the survey is now published in the online version of the Proceedings of the National Academy of Sciences. If temperatures were to increase by 2 – 4°C then, so the scientists estimate, at least one element will tip with a one in six chance. If global temperatures were to increase even further then this probability increases to more than one in two (56%). In such a warming scenario the majority of respondents consider the probability of a complete melting of the Greenland ice sheet and a large-scale die-back of the Amazon rainforest to be particularly high. “The results show that the estimated probabilities increase strongly parallel to the progressive scenarios of future warming” Kriegler summarises the expert survey.

The authors write that expert elicitations have occasionally been criticised for not contributing new scientific information as long as they are not backed by new data, modelling or theories. However, in the context of risk analysis such surveys have proven to be a useful tool to summarise expert knowledge for decision makers. “We do not prescribe society specific climate policy measures,” says Hans Joachim Schellnhuber, director of PIK, and coauthor of the article. “But the results of the survey provide further evidence for the need of ambitious climate protection in order to minimize the risks of far-reaching consequences for our entire planet.”…

A squirrel and the Pacific Ocean, shot by Mila Zinkova, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 2.5, Attribution ShareAlike 2.0 and Attribution ShareAlike 1.0 License