Researchers at Columbia University's Earth Institute note the world's oceans play a key role in regulating climate by absorbing more than a quarter of the carbon dioxide that humans produce by burning fossil fuels.
But now, in the first year-by-year accounting of that mechanism during the industrial era, scientists have found the oceans are struggling to keep up with rising emissions.
The researchers estimate the proportion of fossil-fuel emissions absorbed by the oceans since 2000 may have declined by as much as 10 percent due to natural chemical and physical limits on the oceans' ability to absorb carbon.
"The more carbon dioxide you put in, the more acidic the ocean becomes, reducing its ability to hold CO2," said the study's lead author, Samar Khatiwala, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory. "Because of this chemical effect, over time, the ocean is expected to become a less efficient sink of man-made carbon. The surprise is that we may already be seeing evidence for this, perhaps compounded by the ocean's slow circulation in the face of accelerating emissions."
The study that reconstructs the accumulation of industrial carbon in the oceans year by year, from 1765 to 2008, appears in the journal Nature.
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