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Edited by William C. Clark, Harvard University, Cambridge, MA, and approved November 21, 2007 (received for review June 8, 2007)
Abstract
The term “tipping point” commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. Here we introduce the term “tipping element” to describe large-scale components of the Earth system that may pass a tipping point. We critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing, drawing on the pertinent literature and a recent international workshop to compile a short list, and we assess where their tipping points lie. An expert elicitation is used to help rank their sensitivity to global warming and the uncertainty about the underlying physical mechanisms. Then we explain how, in principle, early warning systems could be established to detect the proximity of some tipping points.
Footnotes
- ↵†To whom correspondence may be addressed. E-mail: t.lenton{at}uea.ac.uk or john{at}pik-potsdam.de
↵**This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on May 3, 2005.
Author contributions: T.M.L., H.H., E.K., J.W.H., and H.J.S. designed research; T.M.L., H.H., E.K., J.W.H., W.L., S.R., and H.J.S. performed research; T.M.L., H.H., E.K., and J.W.H. analyzed data; and T.M.L., H.H., E.K., and H.J.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0705414105/DC1.
- Received June 8, 2007.
- © 2008 by The National Academy of Sciences of the USA
Freely available online through the PNAS open access option.
Tipping elements in the Earth's climate system
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