Critical ocean system could be on the verge of collapse due to climate change

Human-induced warming has resulted in an “almost total loss of stability” in the system that drives the currents of the Atlantic Ocean., a new study has warned, raising the worrying prospect that this critical aquatic “treadmill” may be on the verge of collapse.

In recent years, Scientists have warned of weakening South Atlantic tilting circulation (AMOC), which carries hot, salty water from the tropics to northern Europe, then sends cooler water south along the ocean floor. Researchers studying ancient climate change have also found evidence that AMOC can stop abruptly, causing sudden temperature changes and other dramatic changes in global climate systems.

Scientists did not directly observe the slowdown in AMOC. But the new to study, published Thursday in the magazine Nature Climate Change, based on over a century of ocean temperature and salinity data to show significant changes in eight indirect measures of circulating force.

These indicators suggest that AMOC is low, which makes it more susceptible to failures that could throw it off balance, analyzed the author of the study Niklas boers, researcher at the Potsdam Institute for Climate Impact Science in Germany.

If the traffic stops, it could bring extreme cold to Europe and parts of North America, raising sea levels along the eastern seaboard of the United States, and disrupting the seasonal monsoons that provide water to much of the world..

“This helps to better understand how close the AMOC might already be to a tipping point.“, a point Levke Caesar, a climate physicist from Maynooth University who was not involved in the study.

Boers’ analysis does not suggest exactly when the change might occur. But “the mere possibility that the AMOC tipping point is near should be enough motivation for us to take countermeasures,” Caesar said. “The consequences of a collapse would likely be far-reaching”.

AMOC is the product of a gigantic balancing act across the ocean. It starts in the tropics, where high temperatures not only warm seawater, but increase its salt content by causing evaporation. This warm, salty water flows northeast from the coast of the United States to Europe, creating the current we know as the Gulf Stream.

Corn as the current gains latitude, it cools, adding density to water already laden with salt. When it reaches Greenland, it is dense enough to sink deep below the surface. It pushes other submerged waters south toward Antarctica, where it mixes with other ocean currents as part of a global system known as “thermohaline circulation”.

This circulation is at the heart of the Earth’s climate system, playing an essential role in redistributing heat and regulating weather conditions around the world..

As long as the necessary temperature and salinity gradients exist, AMOC is self-sufficient, Boers explained. The predictable physics that make dense water flow and lighter water “rises” keeps circulation in an endless loop.

Corn climate change has altered the balance. Higher temperatures make ocean waters warmer and lighter. An influx of fresh water from melting ice caps and glaciers dilutes the salinity of the North Atlantic and reduces its density. If these waters are not heavy enough to flow, the whole AMOC will stop.

It’s already arrived. Studies suggest that towards the end of the last Ice Age, a huge glacial lake crossed a declining North American ice cap.. Freshwater flooding spilled into the Atlantic, shutting down AMOC and plunging much of the northern hemisphere, especially Europe, into deep cold. Gas bubbles trapped in polar ice indicate the cold snap lasted 1,000 years. Analyzes of plant fossils and ancient artefacts suggest that climate change has transformed ecosystems and caused upheaval in human societies.

“The phenomenon is inherently bistable,” Peter de Menocal, president of the Woods Hole Oceanographic Institution, said of AMOC. “It’s on or off.”

But is it about to be released now? “This is the central question that concerns us allSaid de Menocal, who was not involved in the Boer investigation.

In its 2019 “Special Report on the Ocean and Cryosphere in a Changing Climate”, the United Nations Intergovernmental Panel on Climate Change predicted that AMOC would weaken in this century , but total collapse over the next 300 years was only likely at the worst of times. . case warming scenarios.

The new analysis suggests that “the critical threshold is probably much closer than we expected.”said Boers.

The “restorative forces,” or feedback loops, that keep AMOC moving are in decline, he said. All the indicators analyzed in their study, including sea surface temperature and salt concentrations, have become increasingly variable..

It’s as if AMOC is a newcomer to the emergency room, and Boers has provided scientists with an assessment of his vital signs, de Menocal said. “All signs are consistent with the patient having a real life threatening problem”.

Physical oceanographers like him are also trying to confirm the slowdown in AMOC through direct observations.. But AMOC is so large and complex that it will likely take years of careful monitoring and data collection before definitive action is possible.

“However, everyone also realizes the danger of waiting for this test.Menocal said.

After all, there are many other indications that the Earth’s climate is in unprecedented territory. This summer, the Pacific Northwest was hit by a heat wave that scientists said was “virtually impossible” without man-made warming. China, Central Europe, Uganda and India have all experienced massive and deadly floods. The wildfires spread from California to Turkey and the frozen forests of Siberia.

The world is more than 1 degree Celsius (1.8 degrees Fahrenheit) hotter than it was before humans started burning fossil fuels, and it’s getting hotter.

And the apparent consequences of the AMOC slowdown are already being felt. A persistent “cold spot” in the ocean south of Greenland is believed to be due to cooler water reaching that region.. The delayed Gulf Stream has caused unusually high sea level rise along the eastern seaboard of the United States. Major fisheries have been disrupted by rapid changes in temperature, and beloved species are struggling to cope with the changes.

If AMOC is completely closed, the change would be irreversible in human lives, Boers said. The “bistable” nature of the phenomenon means that it will find a new equilibrium in its “off” state. Relighting it would require a much larger time change than the changes that triggered the shutdown.

“This is one of those things that shouldn’t happen, and we need to do everything we can to reduce greenhouse gas emissions as quickly as possible.“The Boers have alerted. “It’s a system we don’t want to play with”.

© The Washington Post

Author Sarah Kaplan is a climate journalist covering humanity’s response to global warming who has previously reported on Earth and Universe Sciences.