The Atlantic circulation underlying the Gulf Stream, the weather system that brings warm and mild weather to Europe, is at its weakest in more than a millennium, and according to new data, the disruption of the climate is the probable cause.
Further weakening of the Atlantic Meridional Overturning Circulation (AMOC) could lead to more storms threatening the UK, more winters and an increase in harmful heat waves and droughts in Europe.
Scientists predict that the AMOC will weaken further if global warming continues and could decrease by about 34% to 45% by the end of this century, which could bring us close to a “tipping point” at which the system could become irreversibly unstable. A weakened Gulf Stream would also raise sea levels on the Atlantic coast of the US, with potentially disastrous consequences.
Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research, co-author of the study published in Nature Geoscience on Thursday, told the Guardian that a weakening AMOC would increase the number and severity of storms hitting Britain and will bring more heat waves to Europe.
He said the circulation has already slowed by about 15%, and its impact is being seen. “In 20 to 30 years, it will probably weaken further, and it will inevitably affect us again, so we will see an increase in storms and heat waves in Europe, and sea levels will rise on the east coast of the USA,” he said.
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Rahmstorf and scientists from Maynooth University in Ireland and University College London concluded that the current deterioration had not been seen for at least the past 1,000 years, after studying sediments, Greenland ice cores and other authorized data, time. The AMOC has only been measured directly since 2004.
The AMOC is one of the largest circulating systems in the world transporting warm surface water from the Gulf of Mexico to the North Atlantic Ocean, where it cools and salinizes until it sinks north of Iceland, which in turn draws more hot water from the Caribbean Islands. This circulation is accompanied by winds which also help to bring moderate and wet weather to Ireland, the United Kingdom and other parts of Western Europe.
Scientists have long predicted the weakening of the AMOC due to global warming, and they have expressed concern that it would collapse completely. The new study found that any such point is likely decades away, but that the continued high emissions of greenhouse gases will bring it closer.
Rahmstorf said: ‘We run the chance to cause [a tipping point] in this century, and the circulation would decrease within the next century. We’re extremely unlikely to have activated it already, but if we do not stop global warming, it’s increasingly likely that we’ll activate it.
“The consequences of this are so great that even a 10% chance of a failed case would be an unacceptable risk.”
Research in 2018 has also shown a weakening of the AMOC, but the article in Nature Geoscience says it has been unprecedented over the past millennium, a clear indication that human action is to blame. Scientists have previously said a weakening of the Gulf Stream could cause icy winters in Western Europe and unprecedented changes across 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 weather system will not completely break down if the circulation of the ocean becomes unstable, because wind also plays a key role. The circulation used to break down in different conditions, 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 over the past few weeks, but it is also affected like the jet stream by rising temperatures in the Arctic region. Normally, the very cold temperatures over the North Pole create a polar vortex that holds a steady jet of air currents that hold the cold air in place. However, higher temperatures over the Arctic led to a weak and erratic jet stream, which in some cases caused the cold weather to spread much further south, while in other cases warmer weather was brought north, which contributed to the extreme weather conditions in the United Kingdom. Europe and the US over the past few weeks.
Similarly, the Gulf Stream is affected by the melting of Arctic ice, which pours large amounts of cold water into southern Greenland, disrupting the flow of the AMOC. The effects of the variations in the Gulf Stream are seen over much longer periods of time than the variations in the jet stream, but it will also bring more extreme weather as the climate warms.
The weakening of the AMOC could not only cause extreme weather throughout Europe and the east coast of the USA, but it could also have serious consequences for the ecosystems of the Atlantic Ocean, disrupting fish populations and other marine life.
Andrew Meijers, the deputy scientific scientist of polar oceans at the British Antarctic Survey, who was not involved in the study, said: ‘The AMOC has a profound impact on the world climate, especially in North America and Europe, hence this evidence of a continuing weakening of circulation is critical new evidence for the interpretation of future forecasts of regional and global climate.
‘The AMOC is often modeled as a tipping point under a degree of circulating strength, a point at which the relatively stable tilting circulation becomes unstable or even collapses. The constant weakening of the turnaround means that we can find the point, which would have a profound and probably irreversible impact on the climate. ”
Karsten Haustein, of the Climate Services Center in Germany, also independent of the study, said the US could run the risk of stronger hurricanes due to the weakening of the Gulf Stream.
“While the AMOC will not collapse any time soon, the authors warn that the current could become unstable by the end of this century if warming continues unabated,” he said. “This has already increased the risk of stronger hurricanes on the U.S. east coast due to warmer seawater, as well as the circulation patterns across Western Europe that could potentially change.”