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within us. The salt content of our blood plasma
is similar to the salt content of seawater. “The
bones we use to hear with were once gill bones of
sharks,” says Neil Shubin, professor of anatomy
at the University of Chicago and author of Your
Inner Fish: A Journey Into the 3.5 Billion-Year His-
tory of the Human Body. “Our hands are modified
fish fins, and the genes that build our basic body
architecture are shared with worms and fish.”
Despite our intimate connection to the sea,
for most of human history the ocean has been
as strange to us as a distant planet, a realm of
monsters and mayhem. Humans stuck close to
the shore, mostly, and our ignorance about the
ocean was profound. It still is. Scientists have
only a vague understanding of exactly how
ocean currents are driven, or how ocean tem-peratures impact cloud formation, or what crea-
tures thrive in the depths. Far more people have
been to the moon, which is 240,000 miles above
us, than have been to the deepest part of the
ocean, which is seven miles down. Eighty per-
cent of the ocean remains unmapped, unob-
served, unexplored. Marine biologists don’t
know how sharks sleep or an octopus learns to
open a jar.
But scientists know enough to know that the
ocean is in trouble. Largely because of overfish-
ing, 90 percent of the large fish that were here in
the 1950s are now gone. One metric ton of plastic
enters the ocean every four seconds (at this rate,
there will be more plastic than fish in the ocean
by 2050). But the biggest problem, thanks large-
ly to our insatiable appetite for fossil fuels, is thatthe ocean is heating up fast. The past five years
have been the five warmest ever measured in the
ocean, with 2019 the hottest ever. According to
one study, the amount of heat being added to the
ocean is equivalent to every person on the planet
running 100 microwave ovens all day and night.
Until now, the ocean has been the hero of the
climate crisis — about 90 percent of the addition-
al heat we’ve trapped from burning fossil fuels
has been absorbed by it. “Without the ocean, the
atmosphere would be a lot hotter than it already
is,” says Ken Caldeira, a climate scientist at Stan-
ford University. But the heat the ocean absorbed
has not magically vanished — it’s just stored in
the depths and radiated out later. By absorbing
and slowly releasing heat, the ocean reduces the
volatility of our climate, cushioning the highs
and lows as temperatures change from day to
night, winter to summer. It also means the heat
will continue to seep out for centuries to come,
slowing any human efforts to cool the planet.
“The ocean is the main driver of our climate
system,” Hans-Otto Pörtner, a scientist at the
Alfred Wegener Institute for Polar and Marine
Research in Germany, tells me. One of the cen-
tral functions of the ocean, Pörtner says, is to
redistribute heat from the tropics toward the
poles via deep currents like the Gulf Stream sys-
tem, which begins in the Southern Ocean near
Antarctica, flows across the equator, up to the
Arctic and back again. “Even small changes in
that system can have large impacts on things
like the size and intensity of storms, rainfall
patterns, sea- level rise,” says Pörtner, “and of
course the habitats of all the creatures that live
in the ocean.”
The ocean is also one of the main drivers of
many regional economies. In Alaska, one of the
fastest-changing parts of the planet, the seafood
industry employs more than 50,000 workers,
earning $2 billion in total annual income. Across
the U.S., fishing, ocean farming, shipping, ocean
tourism and recreation support 3.25 million jobs
and contribute about $300 billion to the U.S.’s
annual gross domestic product. No one thinks
this blue economy is going to vanish overnight,
but as fish and other species migrate to cool wa-
ters or die off from temperature changes, there
can be profound impacts on local fisheries — just
ask the cod fishermen in Alaska, or shrimpers in
the Gulf of Maine, who have been wiped out by
rapidly warming waters in the Atlantic.
Pörtner is one of the lead authors of a recent
report on the ocean and cryosphere by the Inter-
governmental Panel on Climate Change. It was
the IPCC’s first report to focus specifically on the
world’s oceans and ice — it was a massive proj-
ect, the work of 105 scientists over a three-year
period. There is a lot of nuance in the report,
but the basic message is clear: In the coming
decades, the ocean will get hotter, more acidic,
IMAGINECHINA/NEWSCOM with less oxygen and less biodiversity. Seas will