Ancient ice cores give clues to effects of global warming

Posted by Kate Taylor

A new study indicates that the last interglacial period may give us a picture of where the planet is headed now, as greenhouse gases increase and temperatures rise.

Results from the NEEM deep ice core drilling project, led by the University of Copenhagen, show that during the Eemian period, between 130,000 and 115,000 years ago, the temperature in north Greenland was about 14 degrees Fahrenheit warmer than today.

However, the surface of the north Greenland ice sheet was only a few hundred yards lower than it is today, indicating that it contributed less than half of the total sea rise at the time.

About 128,000 years ago, the surface elevation of ice at the area surveyed was more than 650 feet higher than it is now - but the ice was starting to thin by about two inches per year. Between about 122,000 and 115,000 years ago, Greenland's surface elevation remained stable at roughly 425 feet below today's.

Calculations indicate Greenland's ice sheet volume was reduced by no more than 25 percent between 128,000 years ago and 122,000 years ago, says CU-Boulder geological sciences professorJim White.

"When we calculated how much ice melt from Greenland was contributing to global sea rise in the Eemian, we knew a large part of the sea rise back then must have come from Antarctica," he says.

"A lot of us had been leaning in that direction for some time, but we now have evidence that confirms that the West Antarctic ice sheet was a dynamic and crucial player in global sea rise during the last interglacial period."

And this loss of ice mass on the Greenland ice sheet looks a lot like changes seen there in the past 10 years. Temperatures above Greenland have been rising five times faster than average global temperatures in recent years, and Greenland's been losing more than 200 million tons of ice a year for the last decade.

The results from the Nature study provide scientists with a "road map"
"Unfortunately, we have reached a point where there is so much carbon dioxide in the atmosphere it's going to be difficult for us to further limit our impact on the planet," says White.

"Our kids and grandkids are definitely going to look back and shake their heads at the inaction of this country's generation. We are burning the lion's share of oil and natural gas to benefit our lifestyle, and punting the responsibility for it."