Reduction in greenhouse gases caused prehistoric global cooling: Study

February 27th, 2009 - 6:31 pm ICT by IANS  

Washington, Feb 27 (IANS) Ice in Antarctica suddenly appeared about 35 million years ago. For the previous 100 million years the continent had been essentially ice-free.
The question for science has been, why? What triggered glaciers to form at the South Pole?

Matthew Huber, assistant professor of earth and atmospheric sciences at Purdue University, says no evidence of global cooling during the period had been found.

“Previous evidence points paradoxically to a stable climate at the same time this event, one of the biggest climate events in Earth’s history, was happening,” Huber says.

However, a team of researchers found evidence of widespread cooling. Additional computer modelling of the cooling suggests that the cooling was caused by a reduction of greenhouse gases in the atmosphere.

Even after the continent of Antarctica had drifted to near its present location, its climate was subtropical. Then, 35.5 million years ago, ice formed on Antarctica in about 100,000 years, which is an “overnight” shift in geological terms.

“Our studies show that just over thirty-five million years ago, poof, there was an ice sheet where there had been subtropical temperatures before,” Huber says. “Until now we haven’t had much scientific information about what happened.”

Before the cooling occurred at the end of the Eocene epoch, the Earth was warm and wet, and even the north and south poles experienced subtropical climates. The dinosaurs were long gone from the planet, but there were mammals and many reptiles and amphibians.

Then, as the scientists say, poof, this warm wet world, which had existed for millions of years, dramatically changed. Temperatures fell dramatically, many species of mammals as well as most reptiles and amphibians became extinct, and Antarctica was covered in ice and sea levels fell.

The research team found before the event ocean surface temperatures near present-day Antarctica averaged 25 degrees Celsius, said a Purdue release.

Mark Pagani, professor of geology and geophysics at Yale University, says the research found that air and ocean surface temperatures dropped as much as 18 degrees Fahrenheit during the transition.

The study was published this week in Science.

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