There is a reason to be concerned as a new study has thrown up evidence that the Greenland ice sheet melted off completely at least once in the last 2.6 million years. It is a hint that such a possibility cannot be ruled out in this era of global warming.
This follows an analysis of a piece of bedrock excavated from the bottom of the ice summit.
The findings have been published in the journal Nature.
"Our study puts Greenland back on the endangered ice-sheet map," commented Joerg Schaefer, co-author, and Palaeoclimatologist at Columbia University's Lamont-Doherty Earth Observatory, Palisades.
This implies a risky proposition — the current global warming could sink the ice sheet faster than thought earlier and many unknown mechanisms could also be abetting rapid melting.
Endangered Ice Sheet?
Adding to the worry is that such an ice sheet erosion already took place and Greenland ice sheet melted to bedrock when temperatures were less warm than today.
As of now, Greenland contains 684,000 cubic mile mantle of ice and if it melts completely, global sea levels may rise by 24 feet.
The instability of Greenland ice sheet was reiterated by the authors.
The revelation casts doubt on many of the current assumptions that affirm Greenland as a stable ice formation with a long geological legacy.
"Unfortunately, this makes the Greenland ice sheet look highly unstable," added Schaefer.
The study's significance needs to be seen in the background of the human-induced warming already doubling the loss of the Greenland ice. According to the report, since the 1990s, Greenland has shed more than a trillion tons.
Ice loss from Greenland has been a principal cause of a quarter of the current sea-level rise, at the rate of 3 millimeters a year. Projections of sea-level rise during this century are around 3 or 4 feet.
Isotope Analysis Of Bedrock Sample
The analyzed geologic sample was retrieved from the ice sheet's base 23 years ago. Recovered in July 1993 by a U.S. scientific team from the highest part of the ice sheet, the sample was taken out after drilling through 10,000 feet of ice and sediment.
The American team punched 5 feet of solid bedrock to get to the GISP2 bedrock samples.
After keeping in storage for nearly 25 years, the sample was subjected to analysis under high-resolution accelerator mass spectrometers for tracing atoms that can suggest the history of the land surface.
According to the authors, chemical isotopes indicated that the surface was under the open sky for at least 280,000 years during the last 1.4 million years.
Co-author Richard Alley of Pennsylvania State University said the study is not saying that tomorrow, Greenland will sink into the ocean.
Obviously, the message is that heating up the world at the current rate may invite a lot of sea-level rises, though it may take centuries or millennia to manifest.
