Greenland’s ice-free past exposes future risks
Print Edition
THE massive Greenland ice sheet has melted away at least once during the last 1.4 million years, according to a study published on Wednesday, raising fears that manmade climate change could provoke dangerous sea levels.
Bedrock samples retrieved through more than three kilometers (two miles) of ice reveal for the first time that the island’s surface was exposed directly to the atmosphere in the not-so-distant past.
It may have been a single period of up to 280,000 years, or several shorter ones, researchers reported in the journal Nature.
But either way the evidence shows that the island was largely ice-free.
“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said lead author Joerg Schaefer, a palaeoclimatologist at Columbia University in New York.
Covering an area larger than France, Spain and Germany combined, the northern hemisphere’s largest ice block on land is kilometers thick and holds enough frozen water to lift the world’s oceans by more than 7 meters.
Even a couple of meters would swamp cities that are home to hundreds of millions of people and planted with many of the crops that feed them.
The rate of Greenland’s ice loss has doubled since the 1990s.
Taking advantage of new lab techniques, Schaefer and his team detected rare, radioactive chemicals — produced by interactions with cosmic rays from space — in the Greenland bedrock samples, which were collected more than two decades ago.
The two isotopes identified have well-known decay rates which mark their age, and could only have come into being if the ground was ice-free, the researchers said.
It means that the entire, gargantuan ice sheet must have melted down to less than 10 percent of its current size if moonlight or sunlight could shine on the soil from which the sample was extracted.
“This study really nails it down,” said Thomas Stocker, a professor at the University of Bern in Switzerland and co-chair of the UN’s Intergovernmental Panel on Climate Change.
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