Page 28 - ARUBA TODAY

A28 SCIENCE
Thursday 12 april 2018
Study: Global warming is weakening key ocean circulation

By SETH BORENSTEIN lantic coastal waters have
WASHINGTON (AP) — warmed faster than most
Global warming is likely parts of the ocean in re-
slowing the main Atlantic cent decades, researchers
Ocean circulation, which said. Scientists blame glob-
has plunged to its weakest al warming in a couple of
level on record, according ways. Warmer water less-
to a new study. ens the amount of cooling
The slowdown in the circu- and makes it harder for the
lation — a crucial part of water to sink and turn over.
Earth's climate — had been Ice sheets and glaciers in
predicted by computer Greenland are melting and
models, but researchers the fresh water is pouring
said they can now ob- into the area where the
serve it. It could make for water turns over, making
more extreme weather it less salty, less dense and
across the Northern Hemi- therefore less likely to sink.
sphere, especially Europe, There's also more rain and
and could increase sea snow in northern areas and
level rise along the U.S. East more evaporation in south-
Coast, they said. ern areas, altering the flow,
The slowdown also raises Rahmstorf said.
the prospect of a com- "It's a slow change at the
plete circulation shutdown, moment, but we're chang-
which would be a danger- ing it," Caesar said. "One
ous "tipping point," accord- danger is in the unknown
ing to a study in Wednes- of what will happen. We
day's journal Nature . should expect changes."
Such a shutdown was the Rahmstorf and Caesar
premise of the scientifically looked at an established
inaccurate 2004 disaster cold patch — about 2 mil-
movie "The Day After To- lion square miles (5.2 million
morrow." Study authors said square kilometers), or the
a collapse is at least de- size of India and Mexico
cades away but would be combined — as the indi-
a catastrophe. rect measurements for the
"We know somewhere out speed of the AMOC, call-
there is a tipping point ing it a fingerprint of the
where this current system ocean circulation.
is likely to break down," It's clear that the circula-
said study co-author Stefan This image provided by the Potsdam Institute for Climate Impact Research in April 2018 shows tion is weakening, said
Rahmstorf, a climate scien- observed ocean temperature changes since 1870, and currents in the Atlantic Ocean. Colorado State hurricane
tist at the Potsdam Institute Associated Press expert Phil Klotzbach, who
for Climate Impact Re- wasn't part of the studies.
search in Germany. "We still East Coast to the North At- same issue of Nature by meted in recent years, the Decades ago, that would
don't know how far away lantic, where it cools, sinks a different team indicate study concluded. have meant weaker At-
or close to this tipping point and heads south. The faster that the Atlantic's circula- The Gulf Stream, the warm lantic hurricane activity,
we might be. ... This is un- it moves, the more water is tion is the weakest it's been water current where hur- but that hasn't been hap-
charted territory." turned over from warm sur- in about 1,500 years. And ricanes can power up, his- pening and it could mean
Some other scientists are face to cool depths. the slowdown is intensify- torically veers away from there is a difference in
skeptical, citing a scarcity "This overturning circula- ing. the United States around weakening in winter and
of data. tion redistributes heat on Since the middle of the the Carolinas or Virginia. summer, he said. Andreas
The Atlantic meridional our planet," said study lead 20th century, the speed at The Gulf Stream now hugs Schmittner at Oregon State
overturning circulation, author Levke Caesar, a which the ocean moves closer to coast around University, who also wasn't
called AMOC, is a key con- physicist at the Potsdam In- water in the AMOC has New York, and there's a part of the studies, said the
veyor belt for ocean water stitute. "It brings heat from dropped 15 percent, the significantly warmer bulge Potsdam group's analysis
and air, creating weather. the tropics to the high lati- study found, using cold around Maine related to makes sense, adding that
Warm salty water moves tudes." subpolar water tempera- the circulation slowdown, as the world emits more
north from the tropics along The Caesar study and an- tures as an indirect mea- Rahmstorf and Caesar greenhouse gases from
the Gulf Stream off the U.S. other one published in the surement. And it has plum- said. The northern U.S. At- the burning of fossil fuels,
we can expect it to slow
further. But MIT's Carl Wun-
sch said that the paper's
"assertions of weakening
are conceivable, but un-
supported by any data."
And Kevin Trenberth of the
National Center for Atmo-
spheric Research said his
recent work faults regular
cycles in the atmosphere
more than the ocean. q