Even as the world's emissions of carbon dioxide increased, the amount absorbed by the North Atlantic declined precipitously, according to a new 10-year study by scientists at the University of East Anglia.
The level of CO2 uptake halved between the mid-1990s and the years 2002-2005, scientists said. The Southern Atlantic is also slowing its uptake of carbon, but at a much less dramatic rate. The research will be published in the Journal of Geophysical Research.
The absorption of carbon dioxide by the oceans has positive and negative aspects. For years, scientists saw oceans as a saving grace because they were absorbing so much carbon dioxide that would otherwise have gone into the atmosphere, fueling even more rapid global warming. But in recent years, scientists have identified a worrying side effect: the acidification of the oceans. Already, some sea creatures are living in conditions that prevent them from forming the calcium carbonate shells they need for life. Climate change fueled by increasing greenhouse gases in the atmosphere is expected to produce its own effects on the ocean, via added warmth and changed circulation patterns, but acidification results directly from greenhouse gas pollution.
The slowdown of absorption of carbon dioxide is worrying, because it could mean that the oceans are reaching a saturation point, or that there's some mechanism that prevents the oceans from acting as a counter-balance to our emissions of greenhouse gases as they have in the past. As the rate of pollution continues to increase, if the oceans are removing less from the atmosphere, carbon is fueling the greenhouse effect at an even faster rate.
It's the latest possible sign that the world is reaching important thresholds due to greenhouse gas emissions. Also this summer, Arctic ice retreated to record minimum levels.
But, the scientists warned, it's impossible to make claims about the long-term trends associated with ocean absorption of carbon, since measurements have only been taken in recent years.
"Such large changes are a tremendous surprise. We expected that the uptake would change only slowly because of the ocean's great mass," said Ute Schuster, Ph.D., the lead author. "We are cautious about attributing this exclusively to human-caused climate change because this uptake has never been measured before, so we have no baseline to compare our results to. Perhaps the ocean uptake is subject to natural ups and downs and it will recover again."
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