Atlantic Ocean Circulation Is The Weakest in a Millennium, Scientists Say | Environment


The circulation of the Atlantic Ocean that sustains the Gulf Stream, the meteorological system that brings a warm and temperate climate to Europe, is at its weakest in more than a millennium, and climate collapse is the likely cause, according to new data.

Further weakening of the Atlantic Southern Overturning Circulation (AMOC) could lead to more storms to hit the UK, more severe winters, and increased heat waves and damaging droughts across Europe.

Scientists predict that the AMOC will weaken further if global warming continues, and could be reduced by 34% to 45% by the end of this century, which could bring us closer to a “tipping point” where the system could become irrevocably unstable. A weakened Gulf Stream would also raise sea levels on the Atlantic coast of the United States, with potentially disastrous consequences.

Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, a co-author of the study published Thursday in Nature Geoscience, told The Guardian that a weakened AMOC would increase the number and severity of storms hitting Britain and bring more waves of heat to Europe.

He said circulation had already slowed by 15% and impacts were being seen. “In 20 to 30 years it is likely to weaken even further, and that will inevitably influence our climate, so we would see an increase in storms and heat waves in Europe, and sea levels rise on the east coast of States. United, ”he said.

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Rahmstorf and scientists from the University of Maynooth in Ireland and University College London in the United Kingdom concluded that the current weakening had not been seen for at least the last 1,000 years, after studying sediments, Greenland ice cores and other data. indirect ones that revealed past weather patterns on that. time. The AMOC has only been measured directly since 2004.

The AMOC is one of the largest ocean circulation systems in the world, transporting warm surface water from the Gulf of Mexico to the North Atlantic, where it cools and becomes saltier until it sinks north of Iceland, which in turn time draws more warm water from the Caribbean. This circulation is accompanied by winds that also help bring a mild and humid climate to Ireland, the United Kingdom and other parts of Western Europe.

Scientists have long predicted a weakening of the AMOC as a result of global warming and have expressed concern that it could collapse completely. The new study found that that point is likely decades away, but that continued high greenhouse gas emissions will bring it closer.

Rahmstorf said: “We risk unleashing [a tipping point] in this century, and circulation would decline in the next century. It is highly unlikely that we have already caused it, but if we don’t stop global warming, we are more and more likely to cause it.

“The consequences of this are so massive that even a 10% chance of causing a breakdown would be an unacceptable risk.”

Research in 2018 also showed a weakening of the AMOC, but the article in Nature Geoscience says this was unprecedented in the last millennium, a clear indication that human actions are to blame. Scientists have previously said that a weakening of the Gulf Stream could cause freezing winters in Western Europe and unprecedented changes in the Atlantic.

The AMOC is a large part of the Gulf Stream, often described as the “conveyor belt” that brings hot water from the equator. But the larger meteorological system would not completely break down if ocean circulation became unstable, because winds also play a key role. Circulation has been broken before, under different circumstances, for example at the end of the last ice age.

The Gulf Stream is separate from the jet stream that has helped bring extreme weather to the Northern Hemisphere in recent weeks, though like the jet stream, it is also affected by rising temperatures in the Arctic. Normally, the very cold temperatures over the Arctic create a polar vortex that maintains a constant stream of air currents that keep that cold air in place. But higher temperatures in the Arctic have led to a weak and wandering jet stream, which has helped the cold weather spread much further south in some cases, while bringing warmer weather north in others. , contributing to the extremes in weather seen in the UK. Europe and the United States in recent weeks.

Similarly, the Gulf Stream is affected by melting Arctic ice, which dumps large amounts of cold water into southern Greenland, disrupting the flow of the AMOC. The impacts of variations in the Gulf Stream are observed for much longer periods than variations in the Jet Stream, but will also bring more extreme weather as the weather warms.

In addition to causing more extreme weather in Europe and the east coast of the US, the weakening of the AMOC could have serious consequences for Atlantic marine ecosystems, altering populations of fish and other forms of marine life.

Andrew Meijers, British Antarctic Survey’s deputy chief scientist for polar oceans, who was not involved in the study, said: “AMOC has a profound influence on global climate, particularly in North America and Europe, so this evidence of a continued weakening of the circulation is new critical evidence for the interpretation of future projections of the regional and global climate.

“The AMOC is often modeled as having an inflection point below a certain driving force, a point at which the relatively stable tipping circulation becomes unstable or even collapses. The continued weakening of the rollover means that we run the risk of finding that point, which would have profound and probably irreversible impacts on the climate. “

Karsten Haustein of the Center for Climate Services in Germany, also independent from the study, said the United States could be at risk of stronger hurricanes as a result of the weakening Gulf Stream.

“While the AMOC will not collapse anytime soon, the authors warn that the current could become unstable by the end of this century if warming continues unabated,” he said. “The risk of stronger hurricanes on the east coast of the US has already increased due to warmer ocean waters, as well as potentially altering circulation patterns in Western Europe.”

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