Shifting Winds Possibly Ended Last Ice Age
28.06.2010 - Atmosphere & Space, Water & Oceans, Land & Geology, Ice & Snow, Bi-polar
As most scientists are still trying to understand how the Earth emerged from its last ice age, a review paper published this week in the journal Science suggests a global shift in winds as an answer. According to scientists, a chain of events beginning with the melting of the large northern hemisphere ice sheets about 20,000 years ago could have reconfigured the planet’s wind belts.
The paper explains the freshening of the North Atlantic triggered a series of cold spells in Greenland and northern Europe by shutting down the Gulf Stream current. Sea ice then spread across the North Atlantic and profoundly reshaped the planet’s wind belts. This then caused a southward shift of the tropical trade winds, which not only moved rain further south, but also hot air and warm seawater, heating up the southern hemisphere. In turn, the southern hemisphere westerly winds shifted south as well, bringing warm air and seawater to the mid-latitudes.
This shift in westerly winds caused heavy mixing in the Southern Ocean around Antarctica, pumping dissolved carbon dioxide from the water into the air. Ice core records show that between 18,000 and 11,000 years ago atmospheric carbon dioxide levels rose from 185 parts per million to 265 parts per million. (Today levels are 393 parts per million). The boost in carbon dioxide may have prevented Earth from falling into another ice age, the scientists say.
Although long suspecting the major role of carbon dioxide in the last ice age, scientists had been unable to explain the early warming in the southern hemisphere, where glaciers in Patagonia and New Zealand were melting before carbon dioxide levels rose significantly. While some scientists suggest that a change in ocean currents caused this early warming, computer models using ocean circulation to explain the rapid warming in the south were unable to recreate the large temperature jumps seen in the paleoclimate record. Now with the new evidence for shifting winds in the southern hemisphere, scientists have an answer.
