Tipping elements in the Earth's climate system

As we're at the end of the year I thought it might be good to have a little recap on the principal aim of this blog, which is to cover and explain climate tipping points, and then to illustrate this with some new examples of effected systems we haven't covered yet :). 

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.

Timothy Lenton et. al. (2007) offer a formal definition of the term ‘tipping element’, “to describe subsystems of the Earth system that are at least subcontinental in scale and can be switched—under certain circumstances—into a qualitatively different state by small perturbations. The tipping point is the corresponding critical point—in forcing and a feature of the system—at which the future state of the system is qualitatively altered”.

Human activities may have the potential to push components of the Earth system past critical states into qualitatively different modes of operation, implying large-scale impacts on human and ecological systems. 

Notable examples include the potential collapse of the Atlantic thermohaline circulation (THC) (Rahmstorf and Ganopolski, 1999) and dieback of the Amazon rainforest (Cox et. al., 2000).

A shutoff in North Atlantic Deep Water formation and the associated Atlantic THC can occur if sufficient freshwater (and/or heat) enters the North Atlantic to halt density-driven North Atlantic Deep Water formation. However the IPCC (2007) argues that an abrupt transition of the THC is “very unlikely” (probability <10%) to occur before 2100 and that any transition is likely to take a century or more.

A large fraction of precipitation in the Amazon basin is recycled, and, therefore, simulations of Amazon deforestation typically generate ≈20–30% reductions in precipitation (Zeng et. al., 1996), lengthening of the dry season, and increases in summer temperatures (Kleidon and Heimann, 2000) that would make it difficult for the forest to reestablish, and suggest the system may exhibit bistability.

Hope you have a good new year, in 2014 we’ll use Lenton, 2007, further to illustrate all the most likely potential policy relevant tipping points across the globe as well as have at more in depth look at our above case studies. Not to mention a few other randoms I hope.

Check out the full article here: http://www.pnas.org.libproxy.ucl.ac.uk/content/105/6/1786.full

References

Cox, P.M. Betts, R.A. Jones, C.D. Spall, S.A. and Totterdell, I.J. (2000) Nature 408:184–187.

IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, eds Solomon, S. Qin, D. Manning, M. Chen, Z. Marquis, M. Averyt, K.B. Tignor, M. and Miller, H.L. Cambridge Univ Press,Cambridge, UK.

Kleidon, A. and Heimann, M. (2000) Clim Dyn 16:183–199.

Lenton, T.M. Held, H. Kriegler, E. Hall, J.W. Lucht, W. Rahmstorf, S. Schellnhuber, H.J. (2008)
Tipping elements in the Earth’s climate system. Proc. Natl Acad. Sci. USA 105, 1786–1793.

Rahmstorf, S. Ganopolski, A. (1999) Clim Change 43:353–367.

Zeng, N. Dickinson, R.E. and Zeng, X. (1996) J Clim 9:859–883.