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<div class="header reader-header reader-show-element"> <a
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href="https://www.theguardian.com/environment/2021/aug/05/climate-crisis-scientists-spot-warning-signs-of-gulf-stream-collapse?CMP=fb_gu">theguardian.com</a>
<h1 class="reader-title">Climate crisis: Scientists spot warning
signs of Gulf Stream collapse</h1>
<p>Thu 5 Aug 2021 16.08 BST</p>
<div class="credits reader-credits">Damian Carrington</div>
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<div class="reader-estimated-time" dir="ltr">4-6 minutes</div>
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<p>Climate scientists have detected warning signs of the
collapse of the Gulf Stream, one of the planet’s main
potential tipping points.</p>
<p>The research found “an almost complete loss of
stability over the last century” of the currents that
researchers call the Atlantic meridional overturning
circulation (AMOC). The currents are <a
href="https://www.theguardian.com/environment/2018/apr/11/critical-gulf-stream-current-weakest-for-1600-years-research-finds"
data-link-name="in body link">already at their slowest
point in at least 1,600 years</a>, but the new
analysis shows they may be nearing a<u> shutdown.</u></p>
<p><u>Such an event would have catastrophic consequences
around the world, severely disrupting the rains that
billions of people depend on for food in India, South
America and West Africa; increasing storms and
lowering temperatures in Europe; and pushing up the
sea level in the eastern North America. It would also
further endanger the Amazon rainforest and Antarctic
ice sheets.</u></p>
<p>The complexity of the AMOC system and uncertainty over
levels of future global heating make it impossible to
forecast the date of any collapse for now. It could be
within a decade or two, or several centuries away. But
the colossal impact it would have means it must never be
allowed to happen, the scientists said.</p>
<p>“The signs of destabilisation being visible already is
something that I wouldn’t have expected and that I find
scary,” said Niklas Boers, from the Potsdam Institute
for Climate Impact Research in Germany, who did the
research. “It’s something you just can’t [allow to]
happen.”</p>
<p>It is not known what level of CO2 would trigger an AMOC
collapse, he said. “So the only thing to do is keep
emissions as low as possible. The likelihood of this
extremely high-impact event happening increases with
every gram of CO2 that we put into the atmosphere”.</p>
<p>Scientists are increasingly concerned about tipping
points – large, fast and irreversible changes to the
climate. Boers and his colleagues reported in May that a
significant part of the Greenland ice sheet is <a
href="https://www.theguardian.com/environment/2021/may/17/greenland-ice-sheet-on-brink-of-major-tipping-point-says-study"
data-link-name="in body link">on the brink</a>,
threatening a big rise in global sea level. Others have
shown recently that the Amazon rainforest is now<a
href="https://www.theguardian.com/environment/2021/jul/14/amazon-rainforest-now-emitting-more-co2-than-it-absorbs"
data-link-name="in body link"> </a>emitting more CO2
than it absorbs, and that the 2020 Siberian heatwave led
to <a
href="https://www.theguardian.com/environment/2021/aug/02/climate-crisis-siberian-heatwave-led-to-new-methane-emissions-study-says"
data-link-name="in body link">worrying releases of
methane</a>.</p>
<figure id="084776bb-ce40-4b58-8cc4-dae7f2e16c26"></figure>
<p><u>The world may already have crossed a series of </u><a
href="https://www.theguardian.com/environment/2019/nov/27/climate-emergency-world-may-have-crossed-tipping-points"
data-link-name="in body link">tipping points</a><u>,
according to a 2019 analysis, resulting in “an
existential threat to civilisation”. A major report
from the Intergovernmental Panel on Climate Change,
due on Monday, is expected to set out the worsening
state of the climate crisis.</u></p>
<p>Boer’s research, published in the journal Nature
Climate Change, is titled “Observation-based
early-warning signals for a collapse of the AMOC”.
Ice-core and other data from the last 100,000 years show
the AMOC has two states: a fast, strong one, as seen
over recent millennia, and a slow, weak one. The data
shows rising temperatures can make the AMOC switch
abruptly between states over one to five decades.</p>
<p>The AMOC is driven by dense, salty seawater sinking
into the Arctic ocean, but the melting of freshwater
from Greenland’s ice sheet is slowing the process down
earlier than climate models suggested.</p>
<p>Boers used the analogy of a chair to explain how
changes in ocean temperature and salinity can reveal the
AMOC’s instability. Pushing a chair alters its position,
but does not affect its stability if all four legs
remain on the floor. Tilting the chair changes both its
position and stability.</p>
<p>Eight independently measured datasets of temperature
and salinity going back as far as 150 years enabled
Boers to show that global heating is indeed increasing
the instability of the currents, not just changing their
flow pattern.</p>
<p>The analysis concluded: “This decline [of the AMOC in
recent decades] may be associated with an almost
complete loss of stability over the course of the last
century, and the AMOC could be close to a critical
transition to its weak circulation mode.”</p>
<p>Levke Caesar, at Maynooth University in Ireland, who
was not involved in the research, said: “The study
method cannot give us an exact timing of a possible
collapse, but the analysis presents evidence that the
AMOC has already lost stability, which I take as a
warning that we might be closer to an AMOC tipping than
we think.”</p>
<p>David Thornalley, at University College London in the
UK, whose work showed the AMOC is at its weakest point
in 1,600 years, said: “These signs of decreasing
stability are concerning. But we still don’t know if a
collapse will occur, or how close we might be to it.”</p>
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