Global Warming Causing Slowdown Of Overturning Circulation: Study

A new study released in Nature Climate Change warns that global warming is causing a slowdown in the great ocean circulation, the Washington Post reports.

As the effects of global warming take hold, an inevitable rise in sea levels will prove devastating for much of the U.S., as well as Canada and Mexico. Densely populated coastal cities like New York would be particularly vulnerable, the study says.

Stefan Rahmstorf, who co-authored the study for the Potsdam Institute for Climate Impact Research, says the cause of the slowdown is attributed to global warming.

The “Atlantic meridional overturning circulation” is the scientific name for the conveyor system that travels northwards to Greenland and back down, bringing cool water to North America’s east coast, and warm water to the tropics.

In a typical year, Greenland’s cold salt water will sink deep beneath the surface as it encounters the warmer, less dense Gulf stream waters, ensuring the stability of sea levels along the U.S. and European coasts.

What has scientists startled, however, is that, mostly due to global warming, years of late have not been typical at all.

For instance, despite the winter of 2014-2015 being “the warmest on record for the globe as a whole,” record low temperatures were observed in the far North Atlantic, precisely where the overturning circulation changes direction.

“Indeed, it appears that a particular ocean region of the North Atlantic south of Greenland and between Canada and Britain is becoming colder,” the WP reported.

This increased cooling of North Atlantic waters indicates that less heat is being transported northward, which supports the hypothesis that the overturning circulation is indeed weakening.

What does a weakening overturning circulation mean for us? According to the study authors, it means “seriously bad news” for low-lying cities like New York and Boston.

“Waters to the right or east of the Gulf Stream are warmer than those on its left or west,” Michael Mann of Penn State University said in the study. “Warm water expands and takes up more area than denser cold water, so sea level is also higher to the right side of the current, and lower off our coast.”

A weakened Gulf Stream means a weakened temperature contrast, Mann explained to the WP, which guarantees that sea levels will rise along the U.S. east coast.

This very scenario played out in 2009 and 2010, UANewsreported, as a 4-inch sea level increase was observed along the east coast of the U.S. and Canada.

[Photo Credit: NASA]

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