Globe: Rapid melt shrinks Greenland's ice cap
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Friday, February 17, Rapid melt shrinks Greenland's ice cap, Martin Mittelstaedt, Globe and Mail
The ice sheet sitting atop Greenland is the world's largest storehouse of ice outside Antarctica, and the coldest region of the Northern Hemisphere, but even it appears to be under duress from global warming.
Although the vast ice cap has been melting in fits and starts since the end of the last glaciation, researchers using satellite data and other observations have made an alarming discovery: The rate at which it is shrinking has suddenly begun to accelerate.
It more than doubled between 1996-2005, due mostly to glaciers sliding more quickly into the ocean. Greenland is now adding a volume of water to the North Atlantic every two years that is about equal to the total in Lake Erie.
The finding is significant because it suggests that current estimates of Greenland's contribution to rising sea levels may be far too low.
"The southern half of Greenland is reacting to what we think is climate warming," said Eric Rignot, a scientist at the California Institute of Technology's Jet Propulsion Laboratory. "The northern half is waiting, but I don't think it's going to take long."
The finding was announced yesterday at the American Association for the Advancement of Science annual meeting in St. Louis, Mo., and a paper outlining the research appears in today's issue of the journal Science.
At an AAAS news conference, Dr. Rignot said some of the recent changes in Greenland's ice sheet have been breathtaking. One glacier he studied had not moved much for 60 years, but has recently become one of the fastest moving in the world, sliding 14 kilometres a year.
Scientists have long taken a keen interest in Greenland's ice cap because it is such a huge reservoir of water, and holds an important piece in the puzzle of what might happen to the world as the climate warms due to greenhouse gas emissions.
The new research was based on measurements of the cap taken in 1996, 2000 and 2005. Given the short period, there is a possibility the changes could be part of a natural phenomenon scientists don't know about.
But those studying the melting of glaciers do not think so because the trend observed in Greenland is being seen almost everywhere in the world.
"This is universal, what we're seeing going on. We've never seen anything like this happening," said Shawn Marshall, a glaciologist at the University of Calgary.
Warming is having such a dramatic effect on Greenland's ice because melting water is getting between the bottom of the glaciers and the rock they rest upon, lubricating their slide into the sea.
The Greenland ice cap is almost as large as Mexico, covering most of the island up to a depth of three kilometres.
If it were to melt in its entirety, this ice would release such a torrent of water that sea level would rise by seven metres in the world's oceans, inundating almost every major coastal city in the world. No one is predicting such a deluge, which would take a millennium even in the most pessimistic assessments of the impact of global warming.
But Greenland's disappearing ice is making a measurable contribution to rising sea levels, estimated by Dr. Rignot at about half a millimetre a year, or about 20 per cent of the rise observed in the world's oceans. Over the course of the next century, this would raise sea levels by about five centimetres.
Many scientists expect sea levels will rise by about half a metre over the next century, due mainly to the melting of ice and the expansion of water as its temperature rises due to global warming.
The ice sheet sitting atop Greenland is the world's largest storehouse of ice outside Antarctica, and the coldest region of the Northern Hemisphere, but even it appears to be under duress from global warming.
Although the vast ice cap has been melting in fits and starts since the end of the last glaciation, researchers using satellite data and other observations have made an alarming discovery: The rate at which it is shrinking has suddenly begun to accelerate.
It more than doubled between 1996-2005, due mostly to glaciers sliding more quickly into the ocean. Greenland is now adding a volume of water to the North Atlantic every two years that is about equal to the total in Lake Erie.
The finding is significant because it suggests that current estimates of Greenland's contribution to rising sea levels may be far too low.
"The southern half of Greenland is reacting to what we think is climate warming," said Eric Rignot, a scientist at the California Institute of Technology's Jet Propulsion Laboratory. "The northern half is waiting, but I don't think it's going to take long."
The finding was announced yesterday at the American Association for the Advancement of Science annual meeting in St. Louis, Mo., and a paper outlining the research appears in today's issue of the journal Science.
At an AAAS news conference, Dr. Rignot said some of the recent changes in Greenland's ice sheet have been breathtaking. One glacier he studied had not moved much for 60 years, but has recently become one of the fastest moving in the world, sliding 14 kilometres a year.
Scientists have long taken a keen interest in Greenland's ice cap because it is such a huge reservoir of water, and holds an important piece in the puzzle of what might happen to the world as the climate warms due to greenhouse gas emissions.
The new research was based on measurements of the cap taken in 1996, 2000 and 2005. Given the short period, there is a possibility the changes could be part of a natural phenomenon scientists don't know about.
But those studying the melting of glaciers do not think so because the trend observed in Greenland is being seen almost everywhere in the world.
"This is universal, what we're seeing going on. We've never seen anything like this happening," said Shawn Marshall, a glaciologist at the University of Calgary.
Warming is having such a dramatic effect on Greenland's ice because melting water is getting between the bottom of the glaciers and the rock they rest upon, lubricating their slide into the sea.
The Greenland ice cap is almost as large as Mexico, covering most of the island up to a depth of three kilometres.
If it were to melt in its entirety, this ice would release such a torrent of water that sea level would rise by seven metres in the world's oceans, inundating almost every major coastal city in the world. No one is predicting such a deluge, which would take a millennium even in the most pessimistic assessments of the impact of global warming.
But Greenland's disappearing ice is making a measurable contribution to rising sea levels, estimated by Dr. Rignot at about half a millimetre a year, or about 20 per cent of the rise observed in the world's oceans. Over the course of the next century, this would raise sea levels by about five centimetres.
Many scientists expect sea levels will rise by about half a metre over the next century, due mainly to the melting of ice and the expansion of water as its temperature rises due to global warming.
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