Melting ice in Antarctica could impact ocean currents
JUAN BARRETO/AFP via Getty Images
While the melting of the Greenland ice sheet is expected to slow or even collapse the Atlantic Ocean current that keeps Europe warm, meltwater from West Antarctica could preserve this vital current.
But this will not be enough to prevent major climate changes. The Atlantic Southerly Overturning Circulation (AMOC) would decline by another 60 percent and its full recovery would take 3,000 years.
“I would tend to say: don’t be so quick to say that AMOC is going to collapse,” says Sacha Sinet of Utrecht University in the Netherlands. “But the things I show here don’t change much about what happens in the next century. You probably won’t be alive to say whether or not the AMOC has been stabilized by West Antarctica.”
The AMOC is a system of currents that brings warm surface waters from the tropics to northern Europe, where they cool and sink before flowing south toward Antarctica. The current carries 1.2 petawatts of heat – the equivalent of the energy produced by 1 million power plants – which keeps Europe far warmer than Labrador or Siberia at the same latitude. But light, fresh meltwater from Greenland’s ice should prevent the AMOC’s salty, dense water from sinking, slowing the current.
If the AMOC collapses, winter cold spells could reach nearly -50°C (-58°F) in northern Europe. This week, Iceland said the closure of AMOC posed an “existential” security threat. Sea levels would also be higher along the US east coast, and Africa could suffer more severe droughts.
Recent research has concluded that even if we reach net zero emissions by 2075 and then start removing CO2 from the atmosphere, the risk of an eventual collapse of the AMOC could still be 25%. One study predicted a shutdown within a few decades, while another claimed that Antarctic winds would keep the AMOC in a weakened state.
Meanwhile, the melting of the West Antarctic ice sheet has accelerated in recent decades, and some research suggests it is likely to collapse completely. But it’s unclear what effect this will have on AMOC.
According to simulations by Sinet and his colleagues, the moment of melting is decisive. If a centuries-long pulse of meltwater from Antarctica arrives at the same time as a massive melt from Greenland, it will only accelerate the closure of the AMOC.
However, if Antarctic water arrives about 1,000 years before Greenland’s peak melt, the AMOC will weaken for several hundred years, then recover over the next 3,000 years. Although the AMOC ultimately recovered in all scenarios, this early melting of Antarctica prevented its total collapse and accelerated its resurrection.
This may be because as fresh, light meltwater accumulates around Greenland, the sinking of dense, salty water from the AMOC moves southward, and the current later regains strength as meltwater diminishes from Antarctica.
Although it is unlikely that West Antarctica would melt so early while Greenland melted so late, these results reveal a larger link between the AMOC and Antarctic melting, says Louise Sime of the British Antarctic Survey.
“I don’t think we knew before this study that there was a possibility that changes in Antarctica could alter the impacts of the melting Greenland ice sheet to this extent. [on the AMOC]”, she said.
However, the link should now be investigated with more complex models, as that study did not include possible feedback effects such as changes in wind patterns, which could expand Antarctica’s sea ice, she adds.
Even if the drastic melting of West Antarctica prevented the collapse of the AMOC, it would still cause up to 3 meters of sea level rise, flooding coastal cities.
“Unfortunately, it is no consolation if one disaster can reduce the risk of another disaster,” says Stefan Rahmstorf of the University of Potsdam, Germany.
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