Do warming oceans Portend an Ice Age?

It has been shown for the first time that the deep-ocean circulation system of the North Atlantic, which controls ice-age cycles of cold and warm periods in the Northern Hemisphere, is integrally coupled to salinity levels in the Caribbean Sea. University of California, Davis, research reinforces concerns that global warming, by melting the glacial ice of Greenland, quickly and profoundly could change salinity and temperatures in the North Atlantic Ocean. One consequence might be much colder weather in Northern Europe and Britain and perhaps even in eastern Canada and in the Northeast region of the U.S.

During Earth's warm periods, like the present one, surface ocean currents transport heat from the tropics to the cool northern latitudes. The new data, a record of Caribbean salinity for the past 120,000 years, show that, when the Northern Hemisphere warmed, Caribbean salinity levels dropped. The researchers hypothesize that elevated Caribbean salinity, which is transported via the Gulf Stream to the North Atlantic, amplifies the heat transport system by increasing the deep-ocean circulation rate. When the North Atlantic Ocean cools, the Caribbean's salinity begins building up because the deep ocean circulation drops to a fraction of its previous rate and the Gulf Stream no longer transports salty water away.

If Caribbean salinity helps power the heat-transport system, then what might happen if melting ice from Greenland dilutes the salinity of the North Atlantic at a time when Caribbean salinity is low, like today? "Our atmospheric and oceanic systems are integrally linked," says professor of geology Howard Spero. "Unnatural climate perturbation, such as global warming, can impact ocean circulation and nudge the system towards a threshold that could produce an abrupt climatic change."

The researchers analyzed fossil foraminifera to reconstruct the rise and fall of the temperature and salinity of the Caribbean Sea throughout the last full ice-age cycle, when huge glaciers reached far south into North America and Europe. They then compared those salinity cycles with published reconstructions of ice-age oscillations of deep Atlantic Ocean circulation patterns. The correlations were striking.

"I don't believe the Earth can plummet into an ice age today, but human-caused global warming has the ability to affect climate in ways we haven't seen before and do it very quickly," concludes Spero.

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