Climate’s first tipping point passed in 2007

When Arctic sea ice flipped into a new, less stable state back in 2007 the first major climate tipping point was passed. This is the claim of scientists Tim Lenton and Valerie Levermann in a recent study which analyses climate data from the last 23 years. The study outlines an interconnected web of climate tipping points, some of which make the next ones more likely.  This may speed the world towards the next tipping point – the thaw of a vast expanse of Siberian permafrost.

Global temperatures have already risen by 0.8 °C. Even if humanity stopped all emissions tomorrow, temperatures would still rise by another 0.3 °C, suggesting the permafrost tipping point of 1.5°C is likely to be reached.

Few consequences of climate change are more dramatic than tipping points – a small push unleashes a big change, which may be unstoppable. According to Tim Lenton of the University of Exeter, UK, and Valerie Livina of the UK’s National Physical Laboratory, Earth saw its first tipping point in 2007 when the Arctic sea ice hit a record low.  Not everyone agrees though, Anders Levermann of the Potsdam Institute for Climate Impact Research in Germany argues that the ice loss cannot be called a tipping point because it could still be reversed.

These two tipping points – the Arctic sea ice and permafrost – are the first in a network of points outlined recently by Lenton and Levermann. The pair argue that periods of rapid ice loss in the Arctic will change regional weather patterns, to warm Asia more quickly and speed up the thaw. Like a set of dominoes falling scientists now believe one tipping point may induce the tipping of another.

“We observe more violent changes in the past than our models are capable of simulating,” agrees Ditlevsen. “That points to the idea of dominoes.”

There is good news though, Lenton and Levermann believe that some tipping points could act as a safety valve.  One is the shutdown of the Atlantic thermohaline circulation, a vast current which pumps water around all the Earth’s oceans. It interacts with many of the other areas susceptible to tipping points, including the Greenland and Antarctic ice and may slow the melting progress.

The worst news of all is that there may be no warning of impending flips. The trouble is that the one tipping point we have already passed, according to Lenton – melting of the Arctic sea ice – gave us no warning signs. Ditlevsen is not surprised. He found that there was no warning before similar events during the last ice age either.

So what’s next? According to the temperatures on Lenton and Levermann’s cascade, the collapse of Greenland’s ice sheet would become inevitable shortly after the Yedoma permafrost thaws. This would raise sea levels by 7 metres, though it would take  many centuries.

Sea levels have already been rising for the last 100 years. However, due to a variety of factors levels do not rise evenly says Mahé Perrette of the Potsdam Institute for Climate Impact Research in Germany. He has modelled all of these effects and calculated local sea level rises in 2100 for the entire planet. While the global average rise is predicted to be between 30 and 106 centimetres, he says tropical seas will rise 10 or 20 per cent more, while polar seas will see a below-average rise. Coasts around the Indian Ocean will be hard hit, as will Japan, south-east Australia and Argentina…Sydney, Tokyo and Buenos Aires watch out.

Sourced from The New Scientist


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