Atlantic Ocean circulation nearing ‘devastating’
tipping point, study finds
Collapse in system of currents that helps regulate
global climate would be at such speed that adaptation would be impossible
Jonathan
Watts
@jonathanwatts
Fri 9 Feb
2024 20.00 CET
The
circulation of the Atlantic Ocean is heading towards a tipping point that is
“bad news for the climate system and humanity”, a study has found.
The
scientists behind the research said they were shocked at the forecast speed of
collapse once the point is reached, although they said it was not yet possible
to predict how soon that would happen.
Using
computer models and past data, the researchers developed an early warning
indicator for the breakdown of the Atlantic meridional overturning circulation
(Amoc), a vast system of ocean currents that is a key component in global
climate regulation.
They found
Amoc is already on track towards an abrupt shift, which has not happened for
more than 10,000 years and would have dire implications for large parts of the
world.
Amoc, which
encompasses part of the Gulf Stream and other powerful currents, is a marine
conveyer belt that carries heat, carbon and nutrients from the tropics towards
the Arctic Circle, where it cools and sinks into the deep ocean. This churning
helps to distribute energy around the Earth and modulates the impact of
human-caused global heating.
But the
system is being eroded by the faster-than-expected melt-off of Greenland’s
glaciers and Arctic ice sheets, which pours freshwater into the sea and
obstructs the sinking of saltier, warmer water from the south.
Amoc has
declined 15% since 1950 and is in its weakest state in more than a millennium,
according to previous research that prompted speculation about an approaching
collapse.
Until now
there has been no consensus about how severe this will be. One study last year,
based on changes in sea surface temperatures, suggested the tipping point could
happen between 2025 and 2095. However, the UK Met Office said large, rapid
changes in Amoc were “very unlikely” in the 21st century.
The new
paper, published in Science Advances, has broken new ground by looking for
warning signs in the salinity levels at the southern extent of the Atlantic
Ocean between Cape Town and Buenos Aires. Simulating changes over a period of
2,000 years on computer models of the global climate, it found a slow decline
can lead to a sudden collapse over less than 100 years, with calamitous
consequences.
The paper
said the results provided a “clear answer” about whether such an abrupt shift
was possible: “This is bad news for the climate system and humanity as up till
now one could think that Amoc tipping was only a theoretical concept and
tipping would disappear as soon as the full climate system, with all its
additional feedbacks, was considered.”
It also
mapped some of the consequences of Amoc collapse. Sea levels in the Atlantic
would rise by a metre in some regions, inundating many coastal cities. The wet
and dry seasons in the Amazon would flip, potentially pushing the already
weakened rainforest past its own tipping point. Temperatures around the world
would fluctuate far more erratically. The southern hemisphere would become
warmer. Europe would cool dramatically and have less rainfall. While this might
sound appealing compared with the current heating trend, the changes would hit
10 times faster than now, making adaptation almost impossible.
“What
surprised us was the rate at which tipping occurs,” said the paper’s lead
author, René van Westen, of Utrecht University. “It will be devastating.”
He said
there was not yet enough data to say whether this would occur in the next year
or in the coming century, but when it happens, the changes are irreversible on
human timescales.
In the
meantime, the direction of travel is undoubtedly in an alarming direction.
“We are
moving towards it. That is kind of scary,” van Westen said. “We need to take climate change much more seriously.”
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