The world’s oceans are absorbing less carbon dioxide, which could cause global temperatures to rise even faster than they have risen in past five decades, Yale geophysicist Jeffrey Park found in a recent study.

Park, a professor of geology and geophysics and the director of the Yale Institute for Biospheric Studies, pooled 50 years of data from atmospheric observatories in Hawaii, Alaska and Antarctica. He found oceans now only absorb about 40 percent of atmospheric carbon dioxide, compared to 50 percent half a century ago. Park’s study was published in the Nov. 25 issue of Geophysical Research Letters.

“Human activity has put 10 [to] 20 times more CO2 into the atmosphere than a big El Niño does, and the climate response is big enough to notice,” Park said in an e-mail. “A large proportion of the CO2 we emit is absorbed by the oceans, which are becoming measurably more acidic as a result. If this absorption slows, more of our CO2 stays in the air and adds more greenhouse effect. So climate change will occur faster.”

Park compared a warmer ocean to a glass of warm soda, which has fewer carbon dioxide bubbles than a glass of cold soda.

The oceans play a major role in regulating carbon dioxide levels, Yale geology and geophysics professor Hagit Affek said.

“The increase in CO2 in the atmosphere is half of what we’d expect from how much fossil fuels we burn,” Affek said. “The other half is being absorbed by the oceans and by photosynthesis.”

While human activity has played a role in global warming, Park said he did not think humans have altered how the oceans absorb carbon dioxide. He noted that studies have not found any meaningful way for humans to affect the oceans’ carbon dioxide absorption in the long term. He added that reduced carbon dioxide absorption is more likely caused by a change in underwater currents or an increase in the oceans’ surface temperature.

The idea for this study came to Park when he was writing a problem set for a graduate course in geology and geophysics. He expected to confirm the results of a 1990 study on the same topic, but instead found that the oceans’ ability to absorb carbon dioxide had changed in the intervening two decades.

Park is also a part of a project that monitors the melting of the Greenland ice sheet, which has raised concerns about a potential collapse of the ice sheet. A collapse of the Greenland ice sheet would raise sea levels by seven meters, Park warned.

The study was funded by the Yale Institute for Biospheric Studies.