New research has found that a globe-spanning ocean flow that helps regulate temperatures around the world could be on the brink of collapsing into instability, a development that would impact weather from South America to Europe and possibly cause summer showers in Israel.
The study found that over the past 100 years there has been “an almost complete loss of stability” in the Atlantic meridional overturning circulation, or AMOC, a flow of sea from the south to the north that includes the Gulf Stream.
The AMOC delivers warm water from the tropics to the north and brings cooler, saltier water to the south, distributing heat and energy around the world while also stirring the oceans. Climate scientists, observing a slowdown in the rate of flow, are already worried that the AMOC could pass a critical threshold after which it would sink into instability, with weak circulation halting the necessary flows.
In a paper published last Thursday in Nature Climate Change, researcher Niklas Boers from the Potsdam Institute for Climate Impact Research in Germany said that the system could be close to reaching that point.
“We urgently need to reconcile our models with the presented observational evidence to assess how far from or how close to its critical threshold the AMOC really is,” Boers said in a statement from the Potsdam Institute for Climate Impact Research.
The AMOC is already known to adopt two speeds at different periods. It is either fast and strong — the state it has been in over the past few thousand years — or at a slow, weak pace. It is currently at its weakest in more than a thousand years, the statement said.
Rising temperatures can cause a rapid change from one speed to the other, Boer’s study found.
According to the UK meteorological office, disruption of the AMOC by it becoming unstable could impact atmospheric circulation over Europe, “possibly causing more winter storms in Northern Europe and increasing summer rain around the Mediterranean.”
“Impacts outside of the Atlantic region are less certain, but could affect Asian monsoons and El Nino,” the service said in a 2019 risk management analysis on the AMOC.
Boers examined figures from eight datasets of temperature and salinity in the Atlantic Ocean measured over the past 150 years, concluding they showed global warming is destabilizing the currents.
“A detailed analysis of these fingerprints in eight independent indices now suggests that the AMOC weakening during the last century is indeed likely to be associated with a loss of stability,” Boers said.
Other facts that are influencing the change in the currents are freshwater from the melting of the Greenland ice sheet, melting sea ice, and river run-offs, the statement said.
The study was published before representatives from 195 countries approved a critical UN science report that will provide the most comprehensive and up-to-date assessment yet of the state of Earth’s climate.
“Today, #IPCC’s latest #ClimateReport — #ClimateChange 2021: the Physical Science Basis — was approved and accepted in a historical first virtual approval session,” the Intergovernmental Panel on Climate Change tweeted on Friday.
The report is set to be released on Monday.
IPCC delegates have been locked in virtual negotiations for two weeks, vetting a 30-page “summary for policymakers” — line-by-line, word-by-word — of the underlying scientific report that was years in the making.
The world has changed since its last comprehensive assessment in 2014.
With increasingly sophisticated technology allowing scientists to measure climate change and predict its future path, the report is expected to make for harrowing reading.
It will project global temperature changes until the end of the century under different emissions scenarios.
Based almost entirely on published research, it could forecast — even under optimistic scenarios — a temporary “overshoot” of the 1.5°C target of the Paris Agreement, and upwardly revised estimates for long-term sea level rise.
It is also expected to reflect huge progress in so-called attribution science, which allows experts to link individual extreme weather events directly to man-made climate change.
While the underlying IPCC report is purely scientific, the summary for policymakers is negotiated by national representatives, and therefore subject to competing priorities.
Belgian climate physicist and former IPCC co-chair Jean-Pascal Ypersele, who was party to the negotiations, said the talks were guided by the underlying science.
“I can testify that the authors of the #ClimateReport had the last word on every sentence in the SPM, which really was a Summary FOR (and not BY) policymakers,” he said on Twitter.
‘Most important report’
The report comes less than three months ahead of the COP26 climate talks in Glasgow, which are seen as vital for humanity’s chance of limiting the worst impacts of global warming.
French climatologist Corinne Le Quere congratulated the delegates for finalizing “the text of what I think will be one of the most important scientific reports ever published.”
There will be two further parts to the IPCC’s latest round of climate assessments, known as AR6.
A working group report on climate impacts, a draft of which was exclusively obtained by AFP, is set for release in February 2022.
Another report on solutions for reducing emissions and adapting to climate change will be out the following month.