Doomsday postponed? What to take from the big new Antarctica studies

There’s grim, mixed news out about Antarctica.

Two new papers on melting Antarctic ice come just days after
NASA scientists announced the discovery of
a massive subterranean hole in West Antarctica’s Thwaites
Glacier
, the Florida-sized hunk of ice which alone
could unleash more than two feet of sea-level rise should it
collapse
.

One study found that all this melting could have surprising and
profound impacts on weather while the other (controversial) study
scaled back previous Doomsday estimates. Still, the takeaway from
both studies is clear: If we keep on our current path, things could
go downhill for humanity very, very quickly.

The worst-case scenario that’s emerging is shockingly bad

In
the first paper
, an international team of researchers examined
the impacts of melting ice on global ocean circulation and weather
patterns.

As relatively cool, salt-free meltwater spreads from Antarctica
and Greenland across the world’s oceans, it will have dire
impacts: The circulation of the Atlantic Ocean will slow, changing
how the planet distributes heat, and prompting “a complex pattern
of atmospheric and oceanic changes” worldwide, according to the
paper.

Weather would worsen almost everywhere, with year-to-year swings
in temperature and precipitation increasing in severity by more
than 50 percent, especially in eastern North America.

New Zealand and Iceland may warm at a much slower rate than the
rest of the world, but ice melt at both poles may actually quicken
as heat from the rapidly warming tropical oceans is shunted below
the surface where it can stay for hundreds of years. Sub-surface
ocean currents would then be able to eat away at the undersides of
polar glaciers even more quickly.

In this scenario, sea levels would rise quickly, especially for
small island states in the Pacific which — due to a new quirk in
Earth’s gravity owing to the incredible ice loss at the poles —
would bear the brunt of a reshaped ocean-ice system.

“Melt from these ice sheets is going to significantly disrupt
the global climate, making temperatures in some areas vary much
more from one year to the next,” lead author Nick Golledge said
in a press release. “This unpredictability is going to prove
extremely disruptive for all of us, and will make adaptation and
planning much more difficult.”

The shred of hope in towering ice cliffs

The first paper found that there’s almost no remaining
scenario in which the Thwaites glacier stops melting anytime soon.
Scientists have been increasingly worried about the possibility of
catastrophic failure of the glacier since at least 2016.

Then, a study found that the Thwaites collapse could cause as
much as
eight feet of sea-level rise
(nearly triple previous
estimates). The results were so dire, the study was controversial.
That much sea-level rise would cause,
in the words of climate scientist James Hansen
, “the loss of
all coastal cities … and all their history.”

Wednesday’s
second paper
is one of the first major responses to that
finding. The new paper finds that while we might avoid what Grist
has called an “Ice
Apocalypse
,” it’s not necessarily good news: Sea-level rise
would still exceed that of pre-2016 estimates, though at the lower
end of the recently
released National Climate Assessment
, ordered by the Trump
administration.

Here’s why the scientists revised those estimates: In 2016,
researchers assumed that glaciers’ tall ice cliffs would be
exposed and crash. The new study’s team said ice cliff melting
“is not necessary to explain the past, and therefore it might not
be present in the future — at least, we don’t have much
evidence to support it yet,” according to Tamsin
Edwards
, the paper’s lead author. In other words, the
relatively extreme collapses weren’t necessary to explain past
major episodes of sea-level rise, so Edwards and her team made the
decision to leave them out of their model — just to see what
would happen.

“Leaving it out gives much smaller sea-level contributions,”
she said, about 80 percent less by the end of the century, on
average, than if the ice cliff collapses are included. Though the
discrepancy means this debate is far from settled, she said. If
anything, according to Edwards, her findings point to the need for
closer examination of this process which could jeopardize hundreds
of millions of people.

“We still see a dangerous threat,” Rob DeConto, one of the
authors of the 2016 paper, said in an email to Grist. “I don’t
really see ice fracture as an optional process that can be excluded
from ice sheet models.”

“If the pace of calving we observe in Greenland today someday
becomes widespread around the edges of the vastly bigger Antarctic
ice sheet, it could cause very fast sea-level rise,” DeConto
said. “This was the take home message from our 2016 paper. Based
on all the work that has followed, that basic conclusion remains
unchanged.”

The challenge these findings pose to us

Scientists’ job in Antarctica is incredibly daunting: They
must understand not only how these massive glaciers are responding
to current warming; they need to be able to put that response in
context with evidence from past warm periods over millions of
years, and do it all in one of the most remote places on the planet
— and they must present their findings with the utmost
urgency.

For those of us watching intently from the sidelines, it may
seem like contradicting findings are a sign scientists don’t know
what they’re talking about — but in reality, it means that they
are unable to rule out the very dire possibility that things could
get a whole lot worse. All the news out of Antarctica is just one
big
reason for us to act even more decisively
.

This story was originally published by Grist with the headline
Doomsday postponed? What to take from the big new Antarctica
studies
on Feb 7, 2019.

Source: FS – All – Science – News
Doomsday postponed? What to take from the big new Antarctica studies