Global wind-shift caused Earth’s last ice age to end

A global shift in winds is what led to the end of Earth’s last ice age— an event that ushered in a warmer climate and the birth of human civilization.

It is believed that, 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 they could not explain how the south dealt with the shift so fast.

And now a team of researchers looked for an answer towards a global shift in winds and proposed 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,” he added.

"It's the great global warming of all time. We're trying to answer the puzzle: why does the Earth, when it appears so firmly in the grip of an ice age, start to warm?" said the study's lead author, George Denton, a glaciologist at the University of Maine.

Scientists have long suspected that carbon dioxide played a major role in the last ice age but have had trouble explaining the early warming in the southern hemisphere, where glaciers in Patagonia and New Zealand were melting before carbon dioxide levels rose significantly.

Some scientists suggest that a change in ocean currents, triggered by the freshening of the North Atlantic, caused this early warming.

But computer models using ocean circulation to explain the rapid warming in the south have been unable to recreate the large temperature jumps seen in the paleoclimate record.

Now, with the evidence for shifting southern hemisphere westerlies, the rapid warming is readily explained.

The study has been published in the journal Science.