Greenland Ice Has Sensitive History to Warming

May 8, 2008 -- The idea that Greenland's ice melts sluggishly in response to global warming has long been one hedge against rapid global sea level rise -- but the idea may be wrong, say researchers.

New geologic evidence from the seafloor off the southern tip of Greenland shows that during the two past periods of global warming, the melting of Greenland glaciers was right in synch with rising global temperatures -- rather than lagging behind as models have predicted.

In other words, the ice is very sensitive to global warming and recent losses of ice there could be the beginning of a much larger melt than expected.

"People had thought that there was this thermal lag," said Anders Carlson of the University of Wisconsin in Madison.

But offshore sediments that record the debris that is washed out from valleys when glaciers recede tell another story. As Carlson said, "As soon as it starts warming, it starts to melt."

The evidence, which Carlson and his colleagues present in the May issue of the journal Geology, comes in the form of titanium and iron found in cores of sediments offshore at what's called Eirik Drift.

The only sources for the two elements are land-based rocks which wash out of glacial valleys and into the sea once glaciers melt back and expose the ground to the weather. That process, the scientists figure, is a pretty good sign of a warmer climate.

Those two warmer periods were about 120,000 to 132,000 years ago and 10,000 to nearly 15,000 years ago.