31 July, 2009

Are climate tipping points getting nearer?

“It is almost halfway through the rainy season, and the monsoon in many parts of South Asia continues to remain unreliable. In some places it has been crippling weak, while in others it has been devastatingly intense.”

Reading this report by BBC News’ environmental reporter Navin Singh Khadka (here), I remembered a paper by a group of scientists headed by Thimothy Lenton, of the School of Environmental Sciences, University of East Anglia, and Tyndall Centre for Climate Change Research, “Tipping elements in the Earth’s climate system”, published at the Proceedings of the National Academies of Science, PNAS, early last year (here). There, the authors draw on the pertinent literature and the results of an international workshop to evaluate “policy-relevant tipping elements in the climate system”, in order to “compile a short list.” They also try to assess where their tipping points lie. Tipping points are critical thresholds at which a tiny perturbation can qualitatively alter the state or development of a system. They introduced another term, “tipping element” to describe large-scale components of the Earth system that may pass a tipping point.

Among these tipping elements, they listed the Indian summer monsoon as an element that could be rapidly destabilized, starting to display a more erratic pattern oscillating between extremes of weakness and strength. The other element that could pass the tipping point later on would be the Sahara/Sahel and West African Monsoon.

One of the uncertainties pointed out by the paper was whether the Sahara and surrounding regions would become drier or wetter. A story from National Geographic sent to me by biologist Fabio Olmos, who also called my attention to the BBC News report, points to the second hypothesis. It says that “scientists are now seeing signals that the Sahara desert and surrounding regions are greening due to increasing rainfall.” (here)

It seems that actual events are pointing to approaching climate tipping points.

(Sergio Abranches)

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