Earth’s oceans are taking in an increasing share of humanity’s fossil-fuel carbon, but forests, soils, and other land ecosystems have not expanded their overall absorption since 1990. That split, documented across three decades of atmospheric measurements, suggests the planet’s natural carbon buffers are behaving very differently—and that neither should be treated as an unlimited safety net.
The new findings on ocean and land carbon uptake come from scientists at the University of California San Diego’s Scripps Institution of Oceanography and collaborators. Published in Science on November 12, 2026, the study examined atmospheric oxygen and carbon dioxide records collected from remote monitoring stations between 1990 and 2019. Scripps’ announcement says the approach allowed researchers to separate the portions of human carbon emissions absorbed by the ocean and by land.
Over that period, the ocean absorbed an average of about 2.8 billion metric tons of carbon dioxide annually—roughly 35% of fossil-fuel emissions. Its carbon sink strengthened by approximately 0.63 billion metric tons of carbon per decade. Land ecosystems absorbed about 1 billion metric tons of carbon each year, equivalent to approximately 13% of fossil-fuel emissions, but the researchers found no meaningful long-term increase in that net total.
The measurement strategy is important because carbon uptake on land is not simply a matter of counting trees. New growth can be offset by deforestation, wildfire, drought, soil losses, and other disturbances. By tracking atmospheric oxygen alongside carbon dioxide, the researchers could estimate how much carbon was being removed through ocean processes versus land biology and land-use changes. The study’s authors describe the result as different from many model projections, which have generally expected the land sink to grow as atmospheric carbon dioxide and plant fertilization increase.
A stronger ocean sink is helpful in the short term, but it comes with a serious tradeoff: carbon dioxide absorbed by seawater drives ocean acidification, which can stress shell-forming organisms and disrupt marine food webs. It also does not mean the ocean will continue scaling up indefinitely. The researchers suggest the ocean’s expansion could slow in coming decades, while warming, circulation changes, and altered marine chemistry make its future performance harder to predict.
The findings therefore sharpen the climate-policy message rather than soften it. Natural sinks removed a substantial portion of emissions during the study period, but they did not eliminate the need to cut fossil-fuel use. If land ecosystems cannot keep pace and ocean uptake eventually loses momentum, a larger fraction of every additional ton of emitted carbon will remain in the atmosphere. For scientists, the next task is extending these observations beyond 2019 and determining which regional changes are driving the global pattern; for everyone else, the implication is more immediate: carbon sinks are allies, not substitutes for emissions reductions.
