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Gulf Stream Slowdown May Result in Drastic Impacts

Mar 24, 2015 02:35 PM EDT
Atlantic Meridional Overturning Circulation.

(Photo : Stefan Rahmstorf/PIK)

The Gulf Stream system, one of Earth's most important heat transport systems, is slower than ever before, and researchers warn that it may result in drastic climate impacts, according to a new study.

"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," lead author Stefan Rahmstorf, from the Potsdam Institute for Climate Impact Research (PIK), said in a press 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 better understand the Gulf Stream system, scientists analyzed data gathered from ice-cores, tree-rings and coral, as well as ocean and lake sediments. Using sea-surface and atmospheric temperature data derived from the samples - exploiting the fact that ocean currents are the leading cause of temperature variations in the subpolar North Atlantic - the team was able to reconstruct Gulf temperatures dating back more than a millennium ago.

What they found was not only that the Gulf Stream is the weakest it's been in recorded history - since the year 900 AD - but also that the current slowdown is well outside the norm. This strongly suggests that man-made global warming is to blame.

As humanity continues to burn fossil fuels and pump millions of tons of carbon dioxide into the atmosphere, our world continues to warm. In fact, last year was the hottest on record. So it should come as no surprise that the Greenland ice sheet - the second-largest body of ice on Earth - is rapidly vanishing. It's likely that freshwater melt coming off of Greenland 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. (Scroll to read on...)

(Photo : Pixabay)

"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 Gulf Stream is just one component - albeit, the largest and most powerful - of the system of ocean water flows known as the Atlantic Meridional Overturning Circulation. And while its severe slowdown probably won't create a catastrophic The Day After Tomorrow scenario in which we find ourselves in a new ice age, further weakening could wreak havoc across the globe.

"If the slowdown of the Atlantic overturning continues, the impacts might be substantial," said Rahmstorf. "Disturbing the circulation will likely have a negative effect on the ocean ecosystem, and thereby fisheries and the associated livelihoods of many people in coastal areas. A slowdown also adds to the regional sea-level rise affecting cities like New York and Boston. Finally, temperature changes in that region can also influence weather systems on both sides of the Atlantic, in North America as well as Europe."
What's more, the Gulf Stream system could weaken so much that at some point it may break down completely, resulting in virtually irreversible climate changes.

The results are described in further detail in the appropriately named journal Nature Climate Change.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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