An international team of researchers lead 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.
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 US American “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.”
Reorganization of the Atlantic Thermohaline Circulation: Most
of the experts believe that the ocean circulation will remain stable
under small future warming. However, if global temperatures were to
rise by more than 4°C experts see a significant increase in the
probability of a collapse of the existing system of Atlantic
circulation.
Increased occurrence of the El-Niño phenomenon and large-scale
die-off of the Amazon rainforest: Even if intense warming should
occur some experts do not expect any change of the El-Niño phenomenon.
Others estimate that El-Niño will become more frequent. The continued
existence of the Amazon rainforest depends on these potential changes,
because the El-Niño phenomenon causes drought in the Amazon region. In
case of increased recurrences of El-Niño models indicate that large
parts of the rainforest will die off. Most experts assume a one in two
chance for a large-scale die-back of the rainforest in case of warming
by more than 4°C.
Complete melting of the Greenland Ice Sheet: Even for a warming
by less than 2°C some of the respondents see the risk of a complete
melting of the Greenland ice sheet. For a strong increase of global
temperature by more than 4°C almost all experts expect a melting of the
ice sheet with a high probability of more than one in two.
Disintegration of the West Antarctic ice sheet: There are
significant uncertainties in our knowledge about the response of the
ice sheet to further warming. Therefore, experts differ in their
estimates of the probability of its disintegration. Higher probability
estimates may have been motivated by recent findings of acceleration of
inland glaciers following the disintegration of ice shelfs on the West
Antarctic peninsula.
Article: Elmar Kriegler, Jim W. Hall, Hermann Held,
Richard Dawson, and Hans Joachim Schellnhuber (2009). Imprecise
probability assessment of tipping points in the climate system.
Proceedings of the National Academy of Sciences, Online Early Edition
See also related release:
"Tipping
elements in the Earth's climate system"
For further information please contact the PIK press office:
Phone: +49 331 288 25 07
E-mail: press [at] pik-potsdam.de
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the
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economically independent research institutes and scientific service
facilities. Leibniz Institutes perform strategic and thematically
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