New Report Questions Ice in Greenland

By Jeff Nesbit for US News and World Report.

A new study in Nature indicates that the bedrock at the bottom of Greenland may not have been covered with ice for hundreds of thousands of years during the recent geological past. It’s a finding that, if true, holds huge implications for coastal cities all around the world.

Nearly every scientific estimate of Greenland’s ice sheet stability – as in, how much of the ice sheet remained there at the end of previous ice ages – has said that ice would remain covering Greenland no matter how much the planet warms. Major scientific bodies don’t even take Greenland’s ice sheet into account in predicting future sea level rise.

The new Nature study says that the conservative scientific estimate might be wrong, and that the bedrock of Greenland has been ice-free many times in the past million years.

“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said lead author Joerg Schaefer, a paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory.

As a result of human activity, the loss of ice since the 1990s has doubled, and in the last four years more than a trillion tons of ice have melted into the oceans. But despite these sorts of ice loss rates in recent years, scientists have been exceedingly cautious on this subject. They’ve believed, and written, that there would always be at least some ice on Greenland.

This new study says, no, it’s been bedrock over and over and over for the past million or so years – 280,000 years worth to be exact. Which means that it might not take as much warming as we thought to melt it to bedrock, and that we are almost certain to hit a tipping point a lot sooner than anyone had previously thought. It could take hundreds of years – or it could occur much more rapidly, even over the span of decades. The truth is that no one knows how long it might take for the entire ice sheet to collapse, and the temperature threshold at which it might tip into irreversible decline.

“(This study) doesn’t say that tomorrow Greenland falls into the ocean. But the message is, if we keep heating up the world like we’re doing, we’re committing to a lot of sea-level rise,” Alley said.

The question of Greenland’s ice sheet instability is controversial. Besides questions about when and how much the ice sheet has melted in the immediate past, scientists also continue to argue about what causes it to melt. Is it from water percolating from the surface that literally creates a series of ice rivers underneath, or do massive ice streams cause big icebergs to calve off into the ocean?

“This study shows we are missing something big about how the system works, and we need to find out what it is, fast,” Schaefer said.

Jeff Severinghaus, a paleoclimatologist at Scripps Institution of Oceanography who was not involved in the study, but he said the new evidence of Greenland ice sheet instability was “very direct and incontrovertible.”

The study “challenges some prevailing thought on the stability of the ice sheet in the face of anthropogenic warming,” he said. “We can now reject some of the lowest sea-level projections, because the models underpinning them assume continuous ice cover during the last million years.”

The critical question is the point at which we reach a tipping point – in other words, when has the planet warmed enough so that the entire ice sheet in Greenland starts its inexorable march to the ocean, raising the oceans by 24 feet and inundating every coastal city. Is it when the planet has warmed by about 3.6 degrees Fahrenheit (two degrees Celsius), for instance, which may very well happen in our lifetime at the rate we’re going?