National Geographic News
The world's oceans, which normally gobble up carbon dioxide, are getting stuffed to the gills, according to the most thorough study to date of human-made carbon in the seas.
Between 2000 and 2007, as emissions of the potent greenhouse gas carbon dioxide skyrocketed, the amount of human-made carbon absorbed by the oceans fell from 27 to 24 percent.
In terms of ocean processes, "that's a pretty large drop, and the trend is pretty clear: The ocean can't keep up with [human-made carbon]," said study leader Samar Khatiwala, an oceanographer at Columbia University's Lamont-Doherty Earth Observatory.
(Related: Find out how Earth's "carbon bathtub" is in danger of overflowing.)
Khatiwala is careful to point out that the total uptake of carbon is not declining—the rate is just not growing as fast as it used to.
But if the oceans continue to be overwhelmed by carbon, more of the gas will remain in the already warming atmosphere, the authors say. (See global warming fast facts.)
"Ultimately the ocean is what's controlling what's going on here," said Chris Sabine, a supervisory oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle, Washington, who was not involved in the research.
"It's a big deal that it's becoming less efficient in taking up CO2."
Carbon dioxide easily dissolves in seawater, so the oceans act as gigantic carbon sinks.
The blue part of our planet currently stockpiles about 150 billion tons of carbon. In 2008 the oceans sucked up 2.3 billion tons of carbon—about six years' worth of U.S. gasoline consumption, Khatiwala said.
For their study, Khatiwala and colleagues collected data on seawater temperature and salinity recorded from 1765 to 2008.
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