Science - USA (2021-12-17)

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SCIENCE science.org 17 DECEMBER 2021 • VOL 374 ISSUE 6574 1421

but carved into a series of upside-down val-

leys, some 50 meters deep. These undula-

tions stress the ice shelf, and the team saw

signs of that stress: Fractures had formed at

the apex of each valley, Pettit says. “They’re

just waiting to be activated in a new way.”

At the upstream camp, researchers led

by Britney Schmidt, a planetary scientist at

Cornell University, dug a borehole and sent a

robot called Icefin plunging through it to the

ocean hidden below. Schmidt navigated Ice-

fin to the point where the ice and rock met.

Nearly everywhere—even at the grounding

line itself—the water was 1°C or 2°C above

freezing. Although not unexpected, given the

10-kilometer retreat of the grounding line

in the past decade, the readings were a sure

sign of the extended reach of ocean warming

ushered in by climate change.

During its surveys, Icefin also scanned the

underside of the ice with a laser and found

valleys similar to the downstream ones. Local

variations in water temperature suggested

the valleys create turbulence that draws in

warmer waters, which deepen them, says

Peter Washam, an oceanographer at Cornell.

“They’re really hot spots of melting.”

As detailed in one of three papers about

Thwaites in the journal Cryosphere, com-

puter models of the ice shelf suggest the

extensive surface cracks seen in the past

5 years have opened as ice thinned by melt-

ing grinds into an offshore, undersea moun-

tain, which had long helped hold the ice shelf

back. Several of these cracks, including one

nicknamed “the dagger,” are now extending

toward the middle of the shelf. Once there,

they may trigger the incipient cracks in the

valleys underneath to grow and weaken the

shelf further, Pettit says.

The newest wrinkle is the growth of the

diagonal fractures, which stretch more than

40 kilometers from the grounding line to

the offshore mountain. Although the ice

directly behind the mountain still seems

stuck, GPS stations placed during the first

field season show slippage along the frac-

ture zone is allowing other ice to maneu-

ver around the mountain, which is likely to

speed the shelf ’s collapse. “It’s got enough

freedom now that it can reroute itself

around,” Pettit says.

With several seasons left in the ITGC cam-

paign, researchers will be able to watch the

shelf disintegrate—although they’ll have to

retrieve their instruments before its demise,

with several fissures only 3 kilometers away

from one former campsite. The ice shelf fail-

ure will be a warning that Thwaites, and the

rest of the West Antarctic Ice Sheet, could be-

gin to see significant losses within decades,

especially if carbon emissions don’t start to

come down, Pettit says. “We’ll start to see

some of that before I leave this Earth.” j

NEWS

Scientists see a ‘really, really

tough winter’ with Omicron

Another major pandemic wave seems inevitable. The big

question is how much severe disease it will bring

COVID-

W

hen South African scientists first

alerted the world to the rapid

spread of a new SARS-CoV-2 vari-

ant, some speculated it might not

take off in other countries. Af-

ter all, an earlier variant named

Beta, which dominated in South Africa

between November 2020 and May, did not

spread much beyond its borders and has

since petered out.

Today it’s clear that the world will not

be so lucky this time. Although many ques-

tions remain, scientists feel increasingly

confident that the new arrival, Omicron, is

likely to dramatically alter the trajectory of

the pandemic—and not for the better.

Omicron has now been found in more than

70 countries and is rapidly gaining ground.

As Science went to press, for example, Danish

scientists estimated Omicron was just days

away from replacing Delta as the most com-

mon variant. “What we see is an extraordi-

nary, rapid spread,” says Troels Lillebæk, an

infectious disease researcher at the Univer-

sity of Copenhagen. Despite very high vacci-

nation rates, the country of 5 million is now

seeing more than 6000 cases a day, roughly

twice the number seen during the highest

previous peak. (The growth seemed to show

signs of slowing down early this week, but

that may be in part because the country is

reaching the limits of its testing capability.)

Neighboring Norway, which has about the

same population, is now projecting more

than 100,000 cases a day in a matter of

weeks, unless people drastically reduce

social contacts.

Even if Omicron causes milder disease, as

some scientists hope, the astronomical case

projections mean the outlook is grim, warns

Emma Hodcroft, a virologist at the Univer-

sity of Bern. “A lot of scientists thought

Delta was already going to make this a re-

ally, really tough winter,” she says. “I’m not

sure the message has gotten across to the

people who make decisions, how much

tougher Omicron is going to make this.”

For Hodcroft and other virologists,

immunologists, and epidemiologists, Omi-

cron is another dizzying plunge on the

pandemic roller coaster, right before the

holidays—a time of frenzied phone calls,

By Kai Kupferschmidt

People line up outside a vaccination center in London on 13 December. The United Kingdom is accelerating

its booster program in response to the rise of the Omicron variant.