The oceans absorb nearly a third of the carbon dioxide humans put into the air, and this has helped offset CO2′s potential to warm global temperatures. At least so far: Many researchers think the oceans are struggling to keep pace with rising emissions. Each year they soak up more and more CO2 in absolute terms, but a growing body of evidence suggests that the rate of absorption is slowing, as surface waters warm and seawater chemistry changes. In the North Atlantic, one of the world’s most intense regions for carbon absorption, some researchers have reported a dramatic slowdown as circulation patterns have changed. But not everyone agrees on the rate of the slowdown; for one thing, natural cycles may be getting confounded with manmade effects.
In the latest attempt to get at this question, a group including Galen McKinley of the University of Wisconsin and Taro Takahashi of Lamont-Doherty Earth Observatory have combined existing data sets from 1981 to 2009. Their study, published in Nature Geoscience this week, looks back about twice as far as others’.
Takahashi, a leading force for decades in cycling of CO2 between air and oceans, says this longer-term look indicates that the slowdown may not be as dire as suggested by previous studies. “If you look at the long-term data, the situation is not that alarming,” he said. But in a press release from U of W, McKinley, the lead author, says the effect is there nevertheless. “This is some of the first evidence for climate damping the ocean’s ability to take up carbon from the atmosphere,” she said.