7 hours ago
https://www.snexplores.org/article/amoc-...-weakening
EXCERPTS: One of Earth’s most vital ocean currents is rapidly weakening. The cause: global warming. A collapse of this current could send devastating ripples through the planet’s climate.
The current is known as the Atlantic Meridional Overturning Circulation. Most scientists just call it AMOC. If it were to shut down, the consequences could be catastrophic and far-ranging. In the worst case: Earth’s warming climate could flip to a deep-freeze. Scientists refer to this scenario as a “snowball Earth.”
AMOC moves warm surface waters in the Atlantic Ocean from the tropics northward toward Europe. This water ferries with it a massive amount of heat. If that transport were to shut down, scientists say, the world might see a host of dramatic weather. Europe could experience more temperature extremes, of both chilling and heating. The Southern Hemisphere would warm even more than it is now. The North Atlantic would trigger stronger storms. The drought in Africa’s Sahel would worsen. And summer rains in Europe could sharply decrease, with devastating outcomes for farmers.
But predictions of how long AMOC will hold out have been all over the map. And it’s only in the last couple of years that scientists have been able to figure out which way the current is really trending. Their consensus: It’s not good — AMOC is weakening.
The stakes are so alarming that some scientists have proposed engineering changes to AMOC. One is building a series of dams to seal off the Bering Strait between Russia and Alaska. By cutting off the northward flow of water from the Strait into the AMOC, the current’s strength might stabilize. At least that’s what researchers claim in a report April 24 in Science Advances.
Such proposed changes are controversial. No one can be sure what unknown impacts they might trigger. And the Science Advances paper “is very much a conceptual study,” says Jelle Soons of Utrecht University in the Netherlands. By that he means it’s a clever idea — but no one yet knows how it might be achieved. And Soons should know. He’s not only a physical oceanographer but also a coauthor of that new report.
What such suggestions can do is focus attention on how serious a threat an AMOC shutdown is — and how little time remains to address it.
[...] Portmann’s team used a branch of math known as statistics to get a less fuzzy estimate. One approach helped simplify complex problems with a lot of variables, like this one. This approach is “not often used in climate science,” Portmann notes, “but is very well known in statistical science.” Called ridge-regularized linear regression, it offered the best match to the problem.
It showed the likelier outcomes were those seen in models whose predictions were more dire. They now suggest AMOC will weaken by about 51 percent (plus or minus 8 percent) by the end of the century.
“What they have shown very convincingly is that, unfortunately, the simulations with the strongest decline are the most realistic ones,” says Rahmstorf. He did not take part in that analysis.
The biggest factor in this correction came from how one factor was weighted: how salty the surface of the future South Atlantic Ocean will be. Researchers had long suspected that the saltier those surface waters would be, the weaker the AMOC would become. The new analysis now supports that link.
And measurements of these waters show they have been getting saltier. One reason is increased evaporation as the oceans have been warming. Another reason: More salty water has been leaking into the South Atlantic from the Indian Ocean as wind patterns shift.
Scientists have identified many things that impact the AMOC besides the salinity of the South Atlantic... (MORE - missing details)
EXCERPTS: One of Earth’s most vital ocean currents is rapidly weakening. The cause: global warming. A collapse of this current could send devastating ripples through the planet’s climate.
The current is known as the Atlantic Meridional Overturning Circulation. Most scientists just call it AMOC. If it were to shut down, the consequences could be catastrophic and far-ranging. In the worst case: Earth’s warming climate could flip to a deep-freeze. Scientists refer to this scenario as a “snowball Earth.”
AMOC moves warm surface waters in the Atlantic Ocean from the tropics northward toward Europe. This water ferries with it a massive amount of heat. If that transport were to shut down, scientists say, the world might see a host of dramatic weather. Europe could experience more temperature extremes, of both chilling and heating. The Southern Hemisphere would warm even more than it is now. The North Atlantic would trigger stronger storms. The drought in Africa’s Sahel would worsen. And summer rains in Europe could sharply decrease, with devastating outcomes for farmers.
But predictions of how long AMOC will hold out have been all over the map. And it’s only in the last couple of years that scientists have been able to figure out which way the current is really trending. Their consensus: It’s not good — AMOC is weakening.
The stakes are so alarming that some scientists have proposed engineering changes to AMOC. One is building a series of dams to seal off the Bering Strait between Russia and Alaska. By cutting off the northward flow of water from the Strait into the AMOC, the current’s strength might stabilize. At least that’s what researchers claim in a report April 24 in Science Advances.
Such proposed changes are controversial. No one can be sure what unknown impacts they might trigger. And the Science Advances paper “is very much a conceptual study,” says Jelle Soons of Utrecht University in the Netherlands. By that he means it’s a clever idea — but no one yet knows how it might be achieved. And Soons should know. He’s not only a physical oceanographer but also a coauthor of that new report.
What such suggestions can do is focus attention on how serious a threat an AMOC shutdown is — and how little time remains to address it.
[...] Portmann’s team used a branch of math known as statistics to get a less fuzzy estimate. One approach helped simplify complex problems with a lot of variables, like this one. This approach is “not often used in climate science,” Portmann notes, “but is very well known in statistical science.” Called ridge-regularized linear regression, it offered the best match to the problem.
It showed the likelier outcomes were those seen in models whose predictions were more dire. They now suggest AMOC will weaken by about 51 percent (plus or minus 8 percent) by the end of the century.
“What they have shown very convincingly is that, unfortunately, the simulations with the strongest decline are the most realistic ones,” says Rahmstorf. He did not take part in that analysis.
The biggest factor in this correction came from how one factor was weighted: how salty the surface of the future South Atlantic Ocean will be. Researchers had long suspected that the saltier those surface waters would be, the weaker the AMOC would become. The new analysis now supports that link.
And measurements of these waters show they have been getting saltier. One reason is increased evaporation as the oceans have been warming. Another reason: More salty water has been leaking into the South Atlantic from the Indian Ocean as wind patterns shift.
Scientists have identified many things that impact the AMOC besides the salinity of the South Atlantic... (MORE - missing details)