Plate Nº 18 · recorded November 14, 2026
Earth & ClimateReported finding
Ocean Carbon Sink Grows While Land Uptake Stalls, 30-Year Data Show
The ocean absorbed 2.8 billion metric tons of carbon yearly from 1990 to 2019 while the land sink stalled, 30 years of Scripps oxygen measurements show.
By Priya Raman4 min read776 words
In brief
- The ocean absorbed 2.8 billion metric tons of carbon per year from 1990 to 2019, about 35% of fossil fuel emissions.
- The ocean sink strengthened by 0.63 billion metric tons of carbon per year each decade.
- The land sink averaged 1 billion metric tons per year, about 13% of emissions, with no long-term growth.
- The study, led by Eric Morgan, was published Nov. 12 in Science.
- Land and ocean sinks together have offset roughly half of all fossil fuel CO₂ emissions.
The ocean absorbed an average of 2.8 billion metric tons of carbon per year between 1990 and 2019 — about 35% of fossil fuel emissions — while the land sink showed no long-term growth at all, according to a study published Nov. 12 in Science.
Scientists at UC San Diego's Scripps Institution of Oceanography drew on more than 30 years of measurements of atmospheric oxygen and carbon dioxide, collected at remote sites by the Scripps O₂ Program. The findings offer some of the strongest observational evidence to date on how the planet's carbon sinks — the natural systems that absorb and store carbon — have changed over time. Together, these sinks have offset roughly half of all fossil fuel emissions, slowing the growth of atmospheric CO₂ and reducing warming.
"Without the land and ocean absorbing half the CO₂ from fossil fuel emissions, we would be living on a very different planet," said Scripps project scientist Eric Morgan, lead author of the study. "But these sinks can't be observed directly. Figuring out exactly how much they have absorbed, and how they have changed over time, is a central goal of carbon cycle research."
How do you measure an invisible sink?
The method rests on a chemical relationship. Scientists have known since the early 1960s that burning coal, gas and oil raises atmospheric CO₂. The same combustion consumes oxygen, so oxygen levels decline as fuels burn. On land, photosynthesis draws CO₂ into plants and releases oxygen. In the ocean, seawater takes up CO₂ through chemical reactions that leave oxygen untouched.
That difference makes oxygen a kind of ledger. The Scripps O₂ Program has collected regular air samples from sites around the world for more than three decades, shipping them to Scripps and measuring both gases in each. Because land and ocean uptake leave distinct signatures in the oxygen record, the researchers could separate how much CO₂ entered the ocean from how much entered land ecosystems.
What did the data show?
The two sinks told sharply different stories:
- The ocean sink absorbed 2.8 billion metric tons (petagrams) of carbon per year from 1990 to 2019, roughly 35% of fossil fuel emissions over that period.
- It strengthened by 0.63 billion metric tons of carbon per year each decade.
- The land sink took up an average of 1 billion metric tons of carbon per year, about 13% of fossil emissions, but swung sharply from decade to decade.
- The land sink peaked in the decade centered on 2009 and has generally declined since.
The strengthening ocean uptake carries a cost. Absorbed carbon lowers seawater pH in a process known as ocean acidification, which harms marine life.
The land result contradicts many computer models, which predict that rising CO₂ and nitrogen should fertilize plant growth and expand the natural land sink. For those models to hold, emissions from deforestation and other land-use changes would need to have risen enough to cancel that growth. Current estimates show those emissions declining instead.
"It was very surprising to see how the net land sink has not kept pace with rising CO₂ levels," Morgan said. "Our data underscore that the land sink may be pretty fragile."
The finding matters because climate models describe the emissions reduction pathways needed to meet any given temperature target. If the models misrepresent the sinks, the study notes, the pathways they project may mislead the global response to climate change.
Could the ocean sink weaken too?
Even the ocean's gains may not last. Warmer water holds less CO₂, and warmer surface waters mix less efficiently into the deep ocean, the reservoir that locks carbon away from the atmosphere for hundreds of years. Both effects could blunt the ocean's future absorption.
Sustaining the measurements is demanding work. "It's not easy to keep these kinds of measurements going year after year, but the payoff for improving our understanding of the carbon cycle is huge," said Ralph Keeling, a professor of geosciences at Scripps and co-author of the study.
A record decades in the making
Keeling founded the O₂ Program in 1989 to track changes in atmospheric oxygen. It now maintains measurements from 10 sampling sites along a Pacific transect running from the high Arctic to the South Pole. The program is a companion to the Keeling Curve, the record of atmospheric CO₂ begun at Mauna Loa by Charles David Keeling in 1958.
The paper is published as Eric J. Morgan et al., "Atmospheric O2 reveals a strengthening ocean carbon sink and a stagnant net land sink since 1990," Science (2026).
Three decades of air samples, and a planet still half-shielding itself from its own emissions.
via phys.org/rss-feed/ (Source)
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Senior reporter covering people, launches and day-to-day practice in general science news at SciBeat.
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