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Tipping elements in the Earth's climate system
- Timothy M. Lenton*,†,
- Hermann Held‡,
- Elmar Kriegler‡,§,
- Jim W. Hall¶,
- Wolfgang Lucht‡,
- Stefan Rahmstorf‡, and
- Hans Joachim Schellnhuber†,‡,‖,**
- *School of Environmental Sciences, University of East Anglia, and Tyndall Centre for Climate Change Research, Norwich NR4 7TJ, United Kingdom;
- ‡Potsdam Institute for Climate Impact Research, P.O. 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, and Tyndall Centre for Climate Change Research, Newcastle NE1 7RU, United Kingdom; and
- ‖Environmental Change Institute, Oxford University, and Tyndall Centre for Climate Change Research, Oxford OX1 3QY, United Kingdom
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Edited by William C. Clark, Harvard University, Cambridge, MA, and approved November 21, 2007 (received for review June 8, 2007)
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Fig. 1.Map of potential policy-relevant tipping elements in the climate system, updated from ref. 5 and overlain on global population density. Subsystems indicated could exhibit threshold-type behavior in response to anthropogenic climate forcing, where a small perturbation at a critical point qualitatively alters the future fate of the system. They could be triggered this century and would undergo a qualitative change within this millennium. We exclude from the map systems in which any threshold appears inaccessible this century (e.g., East Antarctic Ice Sheet) or the qualitative change would appear beyond this millennium (e.g., marine methane hydrates). Question marks indicate systems whose status as tipping elements is particularly uncertain.
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Fig. 2.Method for estimating the proximity to a tipping point. (A) Schematic approach: The potential wells represent stable attractors, and the ball, the state of the system. Under gradual anthropogenic forcing (progressing from dark to light blue potential), the right potential well becomes shallower and finally vanishes (threshold), causing the ball to abruptly roll to the left. The curvature of the well is inversely proportional to the system's response time τ to small perturbations. “Degenerate fingerprinting” (102) extracts τ from the system's noisy, multivariate time series and forecasts the vanishing of local curvature. (B) Degenerate fingerprinting “in action”: Shown is an example for the Atlantic meridional overturning circulation. (Upper) Overturning strength under a 4-fold linear increase of atmospheric CO2 over 50,000 years in the CLIMBER-2 model with weak, stochastic freshwater forcing. Eventually, the circulation collapses without early warning. (Lower) Overturning replaced by a proxy of the shape of the potential (as in A). Although the signal is noisier in Lower than it is in Upper, it allows forecasting of the location of the threshold (data taken from ref. 102). The solid green line is a linear fit, and the dashed green lines are 95% error bars.
Footnotes
- †To whom correspondence may be addressed. E-mail: t.lenton{at}uea.ac.uk or john{at}pik-potsdam.de
- © 2008 by The National Academy of Sciences of the USA
