https://www.wired.com/story/amoc-collapse-atlantic-ocean/
"Off the southwest tip of Iceland, you’ll find what’s often called a “marginal”
body of water. This part of the Atlantic, the Irminger Sea, is one of the
stormiest places in the northern hemisphere. On Google Maps it gets three
stars: “very windy,” says one review. It’s also where something rather strange
is happening. As the rest of the planet has warmed since the 20th century—less
in the tropics, more near the poles—temperatures in this patch of ocean have
hardly budged. In some years they’ve even cooled. If you get a thrill from
spooky maps, check out one that compares the average temperatures in the late
19th century with those of the 2010s. All of the planet is quilted in pink and
red, the familiar colors of climate change. But in the North Atlantic, there’s
one freak splotch of blue. If global warming were a blanket, the Irminger Sea
and its neighboring waters are where the moths ate through. Scientists call it
the warming hole.
The warming hole could be a very big problem. That’s because it’s a sign that
something may be wrong with the Atlantic Meridional Overturning Circulation.
The AMOC is the main current system that crisscrosses the ocean. It flows like
a big river up, down, and across the two hemispheres. All that moving water
performs an amazing service—it’s basically a supremely massive, 1-petawatt heat
pump for the North Atlantic.
The mega-current hauls warm, salty surface water from the tropics near the
Americas up to northern Europe. There the warm water meets cold air and
evaporates. The atmosphere heats up. The water that’s left in the AMOC is now
colder and saltier—which is to say, it’s much denser than the surrounding
water. And if you’re a cod swimming west of Iceland, you’re in for an
astonishing show. Here the heavy AMOC water doesn’t merely sink, it plummets
nearly 3 kilometers down. (Two miles!) Some 3 million cubic meters of water
fall per second, in what amounts to the world’s most record-smashing, invisible
waterfall. This cold river joins up with other falling water—more underwater
cataracts—and crawls through the depths of the ocean, following the topography
of the seabed, all the way to Antarctica. The flow intersects other currents,
things get messy, and eventually the current rises to the surface near South
America and continues its loop.
The big takeaway is a Europe that’s cozier than geography says it should be.
That warm gift—the one where the AMOC dumps much of its heat near
Iceland—helps, for example, the Norwegian city of Tromsø to enjoy temperatures
as warm as –1 degree Celsius in late January, while, at the same latitude in
Canada, Cambridge Bay often gets down to –34 degrees Celsius (or 30 degrees
Fahrenheit and –30 degrees Fahrenheit, respectively). The heat delivery is also
why the northern hemisphere is a few degrees warmer than the southern
hemisphere and why Earth’s warmest latitude is (on average) not the point
closest to the sun—the equator—but 5 degrees north of it.
But, that warming hole. This spot isn’t feeling the full
kapow of rising
global temperatures because, in recent years, less heat has been arriving from
the tropics. Which means the currents must be slowing. By some calculations,
the AMOC’s flow has weakened by 15 percent since the middle of the 20th
century. Looking back further, it is the weakest it has been in a millennium.
Which is alarming. To be sure, the worry is not that the AMOC is on the verge
of a complete stop. The fear is that it will cross a pivotal threshold, and
then begin a decline that is unstoppable."
Via Kenny Chaffin.
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
