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Major Slowdown May Occur in the Gulf Stream System

First Posted: Mar 23, 2015 05:07 PM EDT

The Gulf Stream system is one of Earth's most important heat transport systems. Now, though, scientists have found evidence for a slowdown of this system, which could have major implications for climate.

"It is conspicuous that one specific area in the North Atlantic has been cooling in the past hundred years while the rest of the world heats up," said Stefan Rahmstorf, one of the researchers in a news release. "Now we have detected strong evidence that the global conveyor has indeed been weakening in the past hundred years, particularly since 1970.

In order to learn a bit more about this system, the researchers used sea-surface and atmospheric temperature data. They exploited the fact that the ocean currents are the leading cause of temperature variations in the subpolar north Atlantic. From proxy data gathered from ice-cores, tree-rings, coral and other samples, the researchers reconstructed the system for more than a millennium back in time. In the end, they found the recent changes are unprecedented since the year 900 AD, which hints that they may be caused by global warming.

It's likely that freshwater coming off of the Greenland ice sheet is diluting saltwater and disturbing the oceanic circulation. Less saline water is less dense and therefore has less tendency to sink into the deep. This means that the human-caused mass loss of the Greenland ice sheet may be slowing down the Atlantic overturning.

"Common climate models are underestimating the change we're facing, either because the Atlantic overturning is too stable in the models or because they don't properly account for Greenland ice sheet melt, or both," said Michael Mann, one of the researchers. "That is another example where observations suggest that climate model predictions are in some respects still overly conservative when it comes to the pace at which certain aspects of climate change are proceeding."

The findings are published in the journal Nature Climate Change.

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