CREDITS: (PHOTO NASA ICEBRIDGE/JAMES YUNGEL; (MAP N. DESAI/SCIENCE1420 17 DECEMBER 2021 • VOL 374 ISSUE 6574 science.org SCIENCEA
n alarming crackup has begun at
the foot of Antarctica’s vulnerable
Thwaites Glacier, whose meltwater
is already responsible for about 4%
of global sea level rise. An ice sheet
the size of Florida, Thwaites ends its
slide into the ocean as a floating ledge of
ice 45 kilometers wide. But now, this ice
shelf, riven by newly detected fissures on
its surface and underside, is likely to break
apart in the next 5 years or so, scientists
reported this week at a meeting of the
American Geophysical Union.
The most dramatic sign of impending
failure is a set of diagonal fractures that
nearly span the entire shelf. Last month,
satellites spotted accelerating movement
of ice along the fractures, says Erin Pettit,
a glaciologist at Oregon State University,
Corvallis, who is part of a multiyear cam-
paign to study the glacier. The shelf is like
a windshield with a series of slowly open-
ing cracks, she says. “You’re like, I should
get a new windshield. And one day, bang—
there are a million other cracks there.”
Once the ice shelf shatters, large sections
of the glacier now restrained by it are likely
to speed up, says Ted Scambos, a glacio-
logist at the University of Colorado, Boulder,
and a leader of the Thwaites expedition. In a
worst case, this part of Thwaites could triple
in speed, raising the glacier’s contribution to
global sea level to 5%, Pettit says.
Even more worrisome is the process that
has weakened the ice shelf: incursions of
warm ocean water beneath the shelf, which
expedition scientists detected with a robotic
submersible. Because Thwaites sits below
sea level on ground that dips away from the
coast, the warm water is likely to melt its
way inland, beneath the glacier itself, free-
ing its underbelly from bedrock. A collapse
of the entire glacier, which some research-
ers think is only centuries away, would raise
global sea level by 65 centimeters. And be-
cause Thwaites occupies a deep basin intowhich neighboring glaciers would flow, its
demise could eventually lead to the loss of
the entire West Antarctic Ice Sheet, which
locks up 3.3 meters of global sea level rise.
“That would be a global change,” says Robert
DeConto, a glaciologist at the University of
Massachusetts, Amherst. “Our coastlines will
look different from space.”
Regardless of whether the shelf breaks up
in 1 year or 10 years, Pettit and her colleagues
are doing important work, DeConto adds.
The oceans are simply getting too warm
for these marine ice sheets, which formed
in much cooler conditions, he says. “This
marine-based ice is not going to come back.”
Exploring the future of this keystone of
the West Antarctic Ice Sheet is the aim of the
International Thwaites Glacier Collaboration
(ITGC), a multiyear expedition costing more
than $50 million and funded by the United
States and United Kingdom (Science, 14 Oc-
tober 2016, p. 159). The glacier, far from any
research stations, is tough to reach under
the best circumstances, and ITGC’s first sci-
entific campaign on the ice, in the Antarctic
summer of 2019–20, contended with severe
storms. But the team managed to erect sev-
eral temporary camps, including one in the
middle of the ice shelf and another farther
upstream, near the “grounding line” where
the glacier detaches from the continent.
On top of the 300-meter-thick shelf, the
researchers used ground-penetrating radar
to image the underside of the ice. They were
surprised to find it was not flat and smooth,IN DEPTH
0 500
kmWEST
A N TA RCT I CAAmundsen SeaThwaites
GlacierRoss SeaAntarctic
PeninsulaKeystone crackup
An ice shelf buttressing the Thwaites Glacier is
breaking up. That could speed up the glacier’s collapse,
which would raise sea levels by 65 centimeters.At the foot of the Thwaites Glacier is a 45-kilometer-wide ice shelf. It has begun to fall apart.
By Pa u l Vo ose n
CLIMATE CHANGE
Key Antarctic ice shelf is within years of failure
Breakup of shelf holding back Thwaites Glacier will ramp up sea level rise