CLIMATE CRISIS
68 / ROLLING STONE / APRIL 2020
S
EA-LEVEL RISE is driven by a number of
physical processes, including the fact
that as the ocean warms, its water
expands. And even though scientists
often talk about “global” sea-level rise
as if the ocean were one big bathtub,
there is actually considerable local vari-
ation due to changes in the tug of gravity from
melting ice sheets and the rising or sinking of
land along the shore. But for the future of coastal
cities, what really matters are two things: the
rate of carbon emissions in the coming decades,
and how sensitive the big ice sheets in Greenland
and Antarctica are to the warming from those
emissions. Greenland holds enough ice to raise
sea levels about 22 feet; Antarctica holds enough
to raise them more than 200 feet. According to
the IPCC report, the ice sheets in Greenland and
Antarctica are now contributing 700 percent
more to sea levels than two decades ago. In both
cases, the ice melt is being driven largely by the
warming of the ocean.
On a research expedition I took to Antarctica
last year with British and U.S. scientists aboard
the Nathaniel B. Palmer, the big question scien-
tists were trying to answer was how much warm
circumpolar deep water was upwelling onto the
continental shelf and how much of that warm
water was getting beneath the West Antarctic Ice
Sheet, melting it from below. “The ocean holds
the key,” one scientist told me. “To understand
what is happening in West Antarctica, you have
to understand what is happening in the South-
ern Ocean.”
The more scientists learn about ocean and
ice-sheet dynamics, the more concerned they
get. The latest IPCC assessment puts the range of
sea-level rise by 2100 at two feet in a low-emis-
sions scenario, or up to 3.6 feet in a high-emis-
sions scenario, which is about 10 percent higher
than predicted in the last IPCC report, in 2018.
But this is, as Pörtner tells me, “a conservative
number. We are basing it on what we know, not
on processes that we think could happen.”
In fact, virtually every scientist I know who
studies sea-level rise thinks the risk is under-
stated, even if they don’t yet have enough data
or sophisticated-enough climate models to say
by how much. As Richard Alley, a geophysicist
at Penn State and one of the most respected ice
scientists in the world, recently argued: “It could
be two feet of sea-level rise, it could be 15 or 20
feet [by the end of the century]. There is no good
to offset the bad. And the chances of something
really bad are really there.”
In West Antarctica, the ice sheet is particu-
larly vulnerable to melting from below, due to
its contact with ocean water on the edge of the
continent and because the ground beneath the
ice sheet is a reverse slope — warm ocean water
could run down the slope and penetrate deep
underneath the glacier, which could begin a cas-of the Gulf system is a decades- and century-
scale risk, not an overnight event. But the Gulf
Stream doesn’t have to collapse to wreak havoc.
The IPCC report noted that the Gulf Stream sys-
tem slowed down 15 percent in the 20th century.
In the coming years, the report says, it will likely
continue to weaken, intensifying storms and
bringing frigid weather to Northern Europe, as
well as shifting the path of the West African mon-
soon season, which 300 million people in one
of the poorest, most climate-vulnerable areas
depend on to grow food.NATURE IS CHANGE. But humans have stomped on
the accelerator. We are dumping carbon diox-
ide into the atmosphere about 10 times faster
than volcanoes did 250 million years ago, which
cooked the planet, triggering the End-Permian
extinction that wiped out 96 percent of the spe-
cies on Earth and turned the ocean into a life-
less, slimy Jacuzzi. “No one knows
where our modern experiment
with geochemistry will lead,”
writes Peter Brannen in The Ends
of the World: Volcanic Apoca lypses,
Lethal Oceans, and Our Quest to
Understand Earth’s Past Mass Ex-
tinctions, “but in the End-Perm-
ian, massive injections of green-
house gases into the atmosphere
led straight to the cemetery.”
Despite all the massive climate
impacts that are transforming the
ocean now, it’s a long way from
dead. “If we stopped putting car-
bon in the atmosphere today,
most of the species in the ocean
would bounce back,” says Cal-
deira. “It might take some time,
but they will make it back.” Unfor-
tunately, we are not going to stop
putting carbon into the atmo-
sphere today. And it’s less clear
that, even if we did, we could sta-
bilize the ice sheets. But we can
certainly reduce the risk of cata-
strophic collapse.
Tragic images of sea turtles
wrapped in fishing lines and dead
whales on the beach with hun-
dreds of plastic shopping bags in
their stomachs have helped peo-
ple connect the dots between
what they buy at Target and what
happens in the ocean. As a Demo-
cratic presidential candidate, Eliz-
abeth Warren championed “the
Blue New Deal,” which addresses
everything from streamlined per-
mitting for new offshore wind
farms to climate-smart manage-
ment of wild fisheries. Globally,CLIMATE CRISIS
cading collapse in which enormous sheets of ice
begin falling into the sea like a giant pile of ice
cubes. A big concern is how much warm circum-
polar deep water is upwelling near Thwaites gla-
cier, a chunk of ice the size of Florida that is
basically the cork in the bottle for the West Ant-
arctic Ice Sheet. If it goes, the rest of the gla-
ciers behind it could collapse quickly, raising
sea levels more than 10 feet. How fast could this
happen? No one knows for sure.
In Antarctica, small changes in ocean tem-
perature have big implications. A change of even
one or two degrees in the waters that wash up
against the base of the glaciers could cause the
ice to melt. “Before our trip last year, I think I
was already convinced that extensive retreat of
Thwaites is almost inevitable,” Robert Larter, a
marine geophysicist and the chief scientist on
my trip to Antarctica, told me. “But the more re-
search results I see from our trip and others, the
more certain I become.”
Sea-level rise is not the only
potential consequence of melting
glaciers. Thirty years ago, Wal-
lace Broecker, a pioneering cli-
mate scientist at Columbia Uni-
versity’s Lamont-Doherty Earth
Observatory, saw a very different
climate catastrophe developing in
the North Atlantic. Broecker un-
derstood that as the Greenland
Ice Sheet melted, it would dump
huge volumes of fresh water into
the North Atlantic. This would
interfere with circulation of the
Gulf Stream system, which de-
pends on the sinking of dense,
salty water in the Atlantic to drive
the great deepwater current that
circulates warm water from the
tropics up to the North Atlantic.
“The Gulf Stream system is why
the East Coast of the U.S. is much
colder than the western coast of
Europe,” says Stefan Rahmstorf,
a climate scientist at the Potsdam
Institute for Climate Research
in Germany. “If the Gulf system
were to slow down or stop, it
would have a major impact on the
weather of the Northern Hemi-
sphere.” Broecker (who died in
2019) hypothesized that the shut-
down of the system could plunge
Northern Europe into a reign of
snow and ice — which is more or
less the scenario that plays out in
The Day After Tomorrow, a cheesy
2003 disaster flick.
“The Hollywood scenario is
not going to happen,” says Rahm-
storf. In his view, the shutdownGET INVOLVED
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