Normally, a small additional amount of greenhouse gases results in a small amplification of climate change. However, researchers are discussing whether what are called “tipping points” of the climate may exist. At such a point, a small additional amount of greenhouse gases results in a large, and possibly sudden and irreversible, change in the climate. This phenomenon resembles the stability of a canoe or sailboat. If you lean to the side a bit in the boat, it will tilt as well, and then return to its equilibrium position. But if you lean out too far, the boat will suddenly tilt farther and farther in that direction, and then capsize.

A popular example is a discontinuance of the ocean circulation in the North Atlantic (generally called the “Gulf Stream”), which gives Western Europe its relatively mild climate. Another, fairly plausible, tipping point is a collapse of parts of the ice sheets on Greenland and Antartica. Other possible tipping points include the retreat of Arctic sea-ice, the transition from savannahs to woodland ecosystems (and vice-versa), a disturbance of the monsoons, and the loss of coral reefs.

Fig. 1. Abrupt climate changes identified in state-of-the-art climate models (modified from Drijfhout et al., 2015).

Complex climate models indicate that abrupt climate changes are possible in the future, and that in particular the oceans at high latitudes might be affected (Fig. 1). However, these results are not yet sufficient to judge the risk of abrupt changes in climate. While there is no doubt about the existence and cause of global climate change per se, the results of climate models are very uncertain with regard to the existence of tipping points. One reason is that climate change is much more than only the greenhouse effect, which is very well understood scientifically. For tipping points, on the other hand, complex interactions between the atmosphere, the ocean, vegetation, and the ice sheets play a role; and these often cannot yet be represented realistically in the models. So it is not yet certain scientifically which climate tipping points might be triggered in the future. Amd the list of possible tipping points which we have is based more on random findings than on a systematic strategy.

This is why I am working to evaluate as many different models as possible, and to search them systematically for abrupt climate changes. In this way, hitherto hidden tipping points can be revealed, and one can assess how plausible certain tipping points really are. This strategy allows us to estimate the risks of climate change somewhat better.

Publications

  • Bathiany, S., Dijkstra, H., Crucifix, M., Dakos, V., Brovkin, V., Williamson, M. S., Lenton, T. M. & Scheffer, M.: Beyond bifurcation – using complex models to understand and predict abrupt climate change, Dyn. Stat. Clim. Sys., in press

http://climatesystem.oxfordjournals.org/content/early/2016/11/22/climsys.dzw004.

  • Van Nes, E. H., B.M.S. Arani, A. Staal, B. van der Bolt, B.M. Flores, S. Bathiany & M. Scheffer (2016). What do you mean, „tipping point“? Trends in Ecology & Evolution 31, 902-904.

http://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(16)30183-5

  • Lasslop, G., Brovkin, V., Reick, C. H., Bathiany, S. & Kloster, S., 2016: Multiple stable states of tree cover in a global land surface model due to a fire-vegetation feedback. Res. Lett., 43, 6324–633.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069365/full

  • Drijfhout, S., Bathiany, S., Beaulieu, C., Brovkin, V., Claussen, M., Huntingford, C., Scheffer, M., Sgubin, G. & Swingedouw, D., 2015: Catalogue of abrupt shifts in Intergovernmental Panel on Climate Change climate models. Nat. Acad. Sci., 112, E5777-E5786.

http://www.pnas.org/content/112/43/E5777.abstract