Forests and soils aren’t soaking up more of our carbon pollution as climate models expected; the ocean is doing more of the work, 30 years of Scripps air samples show

The ocean has been absorbing a growing amount of the carbon dioxide released by burning fossil fuels since 1990, while forests, soils and other land ecosystems have not increased their net uptake at all, a study led by UC San Diego’s Scripps Institution of Oceanography found.  The study, published Thursday in the journal Science, challenges many computer models that assumed land would absorb more carbon as CO2 levels rise.

What it means

Land and ocean together have soaked up roughly half of fossil fuel emissions, which has slowed warming.  If the land’s share isn’t growing, more depends on the ocean, and that has a cost:  absorbing carbon dioxide makes seawater more acidic, Scripps said.  Warmer water also holds less CO2 and mixes less with the deep ocean, where carbon can stay locked away for centuries, so the ocean may not keep up, Scripps said.  Because climate models help set how fast countries must cut emissions to hit temperature targets, the authors say getting these numbers right matters.

The numbers

From 1990 to 2019, the ocean took in an average of 2.8 billion metric tons of carbon a year, about 35% of fossil fuel emissions, and its uptake grew by about 0.63 billion tons a year each decade, the paper says.  Land took in about 1 billion tons a year, roughly 13%, with big swings from decade to decade.  Its uptake peaked in the decade centered on 2009 and has generally fallen since.  “The land sink may be pretty fragile,” lead author Eric Morgan, a Scripps project scientist, said in the release.

How they measured it

Burning fuel uses up oxygen while adding CO2.  Plants on land release oxygen as they absorb CO2, but the ocean takes in CO2 through chemical reactions that don’t change oxygen.  By tracking both gases in air samples collected for more than 30 years at 10 remote sites from the Arctic to the South Pole, the team could tell how much carbon went into the sea versus onto land.  The program, founded in 1989 by Scripps professor Ralph Keeling, is a companion to the Keeling Curve, the carbon dioxide record Charles David Keeling began at Hawaii’s Mauna Loa in 1958.

Source:  Scripps Institution of Oceanography, Nov. 12, 2026; Morgan et al., Science, Nov. 12, 2026; University of Exeter, Nov. 12, 2026.