Modificações globais dos ventos podem ter introduzido um clima mais quente no fim da última idade do gelo

segunda-feira, junho 28, 2010

Global Wind Shifts May Have Ushered in Warmer Climate at End of Last Ice Age

ScienceDaily (June 27, 2010) — Scientists still puzzle over how Earth emerged from its last ice age, an event that ushered in a warmer climate and the birth of human civilization. In the geological blink of an eye, ice sheets in the northern hemisphere began to collapse and warming spread quickly to the south. Most scientists say that the trigger, at least initially, was an orbital shift that caused more sunlight to fall across Earth's northern half. But how did the south catch up so fast?

Sea ice in the North Atlantic may have reorganized Earth's winds, spreading warmth from the northern hemisphere to south at the end of the last ice age. (Credit: NASA.)

In a review paper published June 25 in the journal Science, a team of researchers look to a global shift in winds for the answer. They propose a chain of events that began with the melting of the large northern hemisphere ice sheets about 20,000 years ago. The melting ice sheets reconfigured the planet's wind belts, pushing warm air and seawater south, and pulling carbon dioxide from the deep ocean into the atmosphere, allowing the planet to heat even further. Their hypothesis makes use of climate data preserved in cave formations, polar ice cores and deep-sea sediments to describe how Earth finally thawed out.

"This paper pulls together several recent studies to explain how warming triggered in the north moves to the south, ending an ice age," said study co-author Bob Anderson, a geochemist at Columbia University's Lamont-Doherty Earth Observatory. "Finally, we have a clear picture of the global teleconnections in Earth's climate system that are active across many time scales. These same linkages that brought the earth out of the last ice age are active today, and they will almost certainly play a role in future climate change as well."

Earth regularly goes into an ice age every 100,000 years or so, as its orientation toward the sun shifts in what are called Milankovitch cycles. At the peak of the last ice age, about 20,000 years ago, with New York City and large parts of Europe and Asia buried under thick sheets of ice, Earth's orbit shifted. More summer sunlight began falling on the northern hemisphere, melting those massive ice sheets and sending icebergs and fresh water into the North Atlantic Ocean.

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Science 25 June 2010:
Vol. 328. no. 5986, pp. 1652 - 1656
DOI: 10.1126/science.1184119

The Last Glacial Termination

G. H. Denton,1 R. F. Anderson,2,3,* J. R. Toggweiler,4 R. L. Edwards,5 J. M. Schaefer,2,3 A. E. Putnam1

A major puzzle of paleoclimatology is why, after a long interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric CO2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres.

1 Department of Earth Sciences and Climate Change Institute, Bryand Global Sciences Center, University of Maine, Orono, ME 04469, USA.
2 Lamont-Doherty Earth Observatory of Columbia University, Post Office Box 1000, Palisades, NY 10964, USA.
3 Department of Earth and Environmental Sciences, Columbia University, New York, NY 10025, USA.
4 Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, Princeton, NJ 08542, USA.
5 Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA.

* To whom correspondence should be addressed. E-mail:


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