Earth's climate can be sensitive, changing after a variety of events. A volcanic eruption or meteorite impact, for instance, can send enough particles into the air to block the sun and cool the climate. A thickening blanket of greenhouse gases can trap heat. And, more commonly, according to some scientists, slight changes in Earth's orientation toward the sun can cause it to cool or warm in so-called Milankovitch cycles (named after the Serbian engineer who first described them). Now, new evidence from a marine sediment core from the deep Pacific points to warmer ocean waters around Antarctica (in sync with the Milankovitch cycle)—not greenhouse gases—as the culprit behind the thawing of the last ice age. Ice cores drawn from Antarctica and Greenland have shown that carbon dioxide (CO2) levels in the atmosphere began to rise at roughly the same time as the vast ice sheets began to melt. But it remained unclear exactly which came first: melting ice and warming seas released more CO2 or more CO2 led to melting ice and warming seas. By studying sediment cores from the deep Pacific near the Philippines, paleoclimatologist Lowell Stott of the University of Southern California in Los Angeles and his colleagues revealed that the temperatures of the deepest seas rose by around 2 degrees Celsius (3.

6 degrees Fahrenheit) at least 1,000 years before sea-surface temperatures. "Even accounting for the uncertainties of the age of CO2, the deep sea warmed substantially before the CO2 began to rise," Stott says. "The deep Pacific is such an enormously large volume of water that [this warming] reflects the input of a tremendous amount of energy into the global system."

View: Full Article | Source: Scientific American