In the geological blink of an eye, ice sheets in the northern hemisphere began to collapse and warming spread quickly to the south, says a study. Most scientists say the trigger was an orbital shift that caused more sunlight to fall across Earth's northern half. But how did the south catch up so fast?
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, moved to the south, ending an ice age. Finally, we have a clear picture of the global teleconnections in Earth's climate system that are active across many time scales," said study co-author Bob Anderson, geochemist at Columbia University's Lamont-Doherty Earth Observatory (CULDEO).
"These same linkages that brought the earth out of the last ice age are active today and they will certainly play a role in future climate change as well," Anderson added.
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, said a university release.At the peak of the last ice age, about 20,000 years ago, with 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.