Tipping Point Alert

 Scientists are increasingly concerned about tipping points – large, fast and irreversible changes to the climate. The world may already have crossed a series of tipping points, according to a 2019 analysis. Perhaps not, according to others.

Now climate scientists have detected warning signs of the collapse of the Gulf Stream, one of the planet’s main potential tipping points.

The research found “an almost complete loss of stability over the last century” of the currents that researchers call the Atlantic Meridional Overturning Circulation (AMOC).

 The currents are already at their slowest point in at least 1,600 years, but the new analysis shows they may be nearing a shutdown.

Such an event would have catastrophic consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America and West Africa; increasing storms and lowering temperatures in Europe; and pushing up the sea level in the eastern US. It would also further endanger the Amazon rainforest and Antarctic ice sheets.

It is impossible to forecast the date of any collapse for now. It could be within a decade or two, or several centuries away.

Levke Caesar, at Maynooth University in Ireland, commented, “The study method cannot give us an exact timing of a possible collapse, but the analysis presents evidence that the AMOC has already lost stability, which I take as a warning that we might be closer to an AMOC tipping than we think.”

David Thornalley, at University College London in the UK, whose work showed the AMOC is at its weakest point in 1,600 years, said: “These signs of decreasing stability are concerning. But we still don’t know if a collapse will occur, or how close we might be to it.”

 But the colossal impact it would have means it must never be allowed to happen, the scientists said.

“The signs of destabilisation being visible already is something that I wouldn’t have expected and that I find scary,” said Niklas Boers, from the Potsdam Institute for Climate Impact Research in Germany, who did the research. “It’s something you just can’t [allow to] happen.” It is not known what level of CO2 would trigger an AMOC collapse, he said. “So the only thing to do is keep emissions as low as possible. The likelihood of this extremely high-impact event happening increases with every gram of CO2 that we put into the atmosphere”.

Boers and his colleagues reported in May that a significant part of the Greenland ice sheet is on the brink of reaching a tipping point, also, threatening a big rise in global sea level. 

Others have shown recently that the Amazon rainforest is now emitting more CO2 than it absorbs, and that the 2020 Siberian heatwave led to worrying releases of methane.