SCIENCE Earth thawed evenly after the Big Chill

A study says Greenland is the only place that doesn't fit the warming pattern.
SCRIPPS HOWARD
Scientists who studied the last scrapes of ice-age glaciers around the world have concluded that most of Earth thawed out simultaneously at the end of the last Big Chill about 17,500 years ago.
Researchers from Columbia University and the University of Maine reported Friday in the journal Science that evidence of glacial termination is closely in sync with rock samples taken from California and New Zealand. They confirmed their results with others published earlier from places as diverse as Montana, Argentina, Australia and Switzerland.
A difficult puzzle
Climate experts have long been puzzled by ice-core records from Greenland that indicated that at least eastern North America lagged behind Antarctica and the rest of the world in warming up by at least 2,000 years.
But Joerg Schaefer of Columbia's Lamont-Doherty Earth Observatory and George Denton of the University of Maine found that almost everywhere they looked, glaciers started to retreat about 17,500 years ago, right on time to conclude a 100,000-year glacial cycle.
"It's amazing that everything fits so well and that every moraine record of the last termination seems to match with rising temperature in the Antarctic and carbon dioxide in the atmosphere," Schaefer said.
"It's especially surprising because Antarctica was classically thought to be too remote and climatically isolated to respond in a synchronous manner with the rest of the planet," he added. However, other recent research using sediment cores and other ancient climate markers have also suggested that the North and South poles have generally warmed up and frozen in tandem for millions of years.
The researchers dated when the glaciers started to retreat at the end of the last ice age using a method called cosmogenic, or surface-exposure, dating. As cosmic rays pass through Earth's atmosphere and into the scoured rock, they form an isotope of the element beryllium at a known, measured pace. The more of the isotope there is in a section of rock, the longer it's been uncovered from the ice.
The only place that does not fit the warming pattern they observed is Greenland, which lagged about 2,500 years behind the rest of the planet in starting to thaw certain glaciers. The researchers believe this may be because the North Atlantic experienced continued, hyper-cold winters during this period that prevented the region from warming year to year.