April 2022, ScientificAmerican.com 11FORUM
COMMENTARY ON SCIENCE IN
THE NEWS FROM THE EXPERTSLast summer, in an unseasonal event, more than 100 miles of
Florida’s coast around Tampa Bay became an oxygen-depleted
dead zone littered with fish along the nearby shoreline. In the
Northwest, Dungeness crabs were washing onto Oregon’s beach-
es, unable to escape from water that has, in dramatic episodes,
be come seasonally depleted of oxygen over the past two decades.
Much of the conversation around our climate crisis highlights
the emission of greenhouse gases and their effect on warming, pre-
cipitation, sea-level rise and ocean acidification. We hear little about
the effect of climate change on oxygen levels, particularly in oceans
and lakes. But water without adequate oxygen cannot support life,
and for the three billion people who depend on coastal fisheries for
income, declining ocean oxygen levels are catastrophic.
As ocean and atmospheric scientists focused on climate, we
believe that oceanic oxygen levels are the next big casualty of glob-
al warming. To stop the situation from worsening, we need to
expand our attention to include the perilous state of oceanic oxy-
gen levels—the life-support system of our planet. We need to accel-
erate ocean-based climate solutions that boost oxygen, including
nature-based solutions such as those discussed at the 2021 Unit-
ed Nations Climate Change Conference (COP26) held in Glasgow.
As the amount of carbon dioxide increases in the atmosphere,
not only does it warm air by trapping radiation, it warms water.
The interplay between oceans and the atmosphere is complex, but
to put it simply, oceans have taken up about 90 percent of the excess
heat created by climate change during the Anthropocene. Bodies
of water can also absorb CO 2 and oxygen but only up to a limit:
warmer water holds less oxygen. This decrease in oxygen content,
coupled with a large-scale die-off of oxygen-generating phytoplank-
ton resulting not just from climate change but from plastic pollu-
tion and industrial runoff, compromises ecosystems, asphyxiating
marine life and leading to further die-offs. Large swaths of the
oceans have lost 10 to 40 percent of their oxygen, and that loss is
expected to accelerate with climate change.
The dramatic loss of oxygen from our bodies of water is com-
pounding climate-related feedback mechanisms described by sci-
entists in many fields, hundreds of whom signed the 2018 Kiel
Declaration on Ocean Deoxygenation. This declaration has cul-
minated in the new Global Ocean Oxygen Decade, a project under
the U.N. Ocean Decade (2021–2030). Yet despite years of research
into climate change and its effect on temperature, we know com-
paratively little about its effect on oxygen levels and what falling
oxygen levels, in turn, may do to the wider earth system.
As the financial world invests in climate change solutions,
possibly including future geoengineering efforts such as iron fer-tilization, we run the risk of exacerbating oxygen loss. We need
to evaluate potential unintended consequences of climate solu-
tions for the full life-support system.
Beyond enhanced monitoring of oxygen and the establish-
ment of an oxygen-accounting system, such an agenda encom-
passes fully valuing the ecosystem co-benefits of carbon seques-
tration by our ocean’s seaweed, seagrasses, mangroves and other
wetlands. These so-called blue carbon nature-based solutions are
also re markable at oxygenating our planet through photosynthe-
sis. At COP26 we saw a lot of primarily terrestrial initiatives and
commitments, such as for forestry management, that are excel-
lent steps forward. We hope the 2021 climate conference and this
year’s COP27 meeting help oceanic nature-based solutions to
come into their own, propelled by the U.N. Ocean Decade.
Putting oxygen into the climate story motivates us to do the
work to understand the deep systemic changes happening in our
complex atmospheric and oceanic systems. Even as we celebrated
the return of humpback whales in recent years to an increasingly
clean New York Harbor and Hudson River, dead fish clogged the
Hudson in the summer as warmer waters carried less oxygen. Eco-
system changes connected to physical and chemical systems-level
data may point the way to new approaches to climate solutions—
ones that encompass an enhanced understanding of the life-sup-
port system of our planet and complement our understanding of
drawdown to reduce emissions of CO 2. Roughly 40 percent of the
world’s people depend on the ocean for their livelihoods. If we do
not save marine life from oxygen starvation, we starve ourselves.JOIN THE CONVERSATION ONLINE
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Breathe
Marine oxygen levels are the next
great casualty of climate change
By Nathalie Goodkin and Julie PullenFish die-off at Madei ra
Beach, Fla., July 2021Nathalie Goodkin is a chemical ocean ographer
and an associate curator at the American
Museum of Natural History. Julie Pullen
leads initiatives in climate risk and climate
solutions. She is an adjunct research scientist
at Columbia University’s Earth Institute.Octavio Jones/Getty Images