Circulation in the Atlantic Ocean at its lowest in a millennium, scientists say | Environment

Circulation in the Atlantic Ocean that underlies the Gulf Stream, the weather system that brings warm and mild weather to Europe, is at its lowest in over a millennium, and climate degradation is the likely cause. , according to new data.

Further weakening of the Atlantic Meridional Turning Circulation (AMOC) could lead to more storms hitting the UK, more intense winters and an increase in damaging heatwaves and droughts across Europe.

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

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

He said the spread had already slowed by around 15% and the effects were visible. “In 20 to 30 years it is likely to weaken further, which will inevitably influence our climate, so we would see an increase in storms and heat waves in Europe, and sea level would rise on the east coast of the United States, ”he said.

Rahmstorf and scientists at Maynooth University in Ireland and University College London in the UK concluded that the current weakening has not been observed for at least the past 1000 years, after studying the sediments , Greenland ice cores and other indirect data that revealed weather patterns of the past. time. AMOC has only been measured directly since 2004.

AMOC is one of the largest ocean circulation systems in the world, carrying 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 draws more warm water from the Caribbean. This circulation is accompanied by winds which also help to bring mild and humid weather to Ireland, the United Kingdom and other parts of Western Europe.

Scientists have long predicted a weakening of AMOC as a result of global warming and have expressed fears that it could collapse altogether. The new study found that such a point would likely be decades away, but still high greenhouse gas emissions would bring it closer.

Rahmstorf said: “We risk triggering [a tipping point] in this century, and traffic would slow down over the next century. It’s extremely unlikely that we have already triggered it, but if we don’t stop global warming, it’s increasingly likely that we will trigger it.

“The consequences are so massive that even a 10% probability of triggering an outage would be an unacceptable risk.”

Research in 2018 also showed a weakening of AMOC, but the Nature Geoscience article indicates that this was unprecedented in the past 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 across the Atlantic.

The AMOC is a large part of the Gulf Stream, often described as the “conveyor belt” that brings warm water to the equator. But the larger weather system wouldn’t collapse entirely if ocean circulation became unstable, as winds also play a key role. The circulation has broken down before, under different circumstances, for example at the end of the last ice age.

The Gulf Stream is separate from the jet stream which has helped bring extreme weather conditions to the northern hemisphere in recent weeks, although, like the jet stream, it is also affected by rising temperatures in the Arctic. Normally, very cold temperatures over the Arctic create a polar vortex that maintains a constant stream of drafts holding that cold air in place. But the warmer temperatures over the Arctic resulted in a weak, wandering jet stream, which helped the cold weather spread much further south in some cases, while bringing warmer weather further north into others, contributing to the weather extremes seen in the UK, Europe and the US in recent weeks.

Likewise, the Gulf Stream is affected by the melting arctic ice, which discharges large amounts of cold water south of Greenland, disrupting the flow of the AMOC. The impacts of variations in the Gulf Stream are seen over much longer periods of time than variations in the jet stream, but will also lead to more extreme weather conditions as the climate warms.

In addition to causing more extreme weather conditions in Europe and the east coast of the United States, the weakening of AMOC could have serious consequences for Atlantic marine ecosystems, disrupting populations of fish and other marine species.

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

“AMOC is often modeled as having a tipping point below a certain circulation force, a point at which the relatively stable turning circulation becomes unstable or even collapses. The continued weakening of the reversal means we risk finding this point, which would have profound and possibly irreversible climate impacts.

Karsten Haustein, of the Climate Services Center in Germany, also independent of the study, said the United States could be at risk of more severe hurricanes due to the weakening Gulf Stream.

“While AMOC isn’t going to collapse anytime soon, the authors warn that the tide 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 US east coast due to warmer ocean waters, as well as the potential change in circulation patterns in Western Europe.