MELTING: Nasa says global warming is responsible for sea level rise in two ways: first because warmer air increases the rate of glacial melting and, second, because the ocean is absorbing most of the extra heat trapped by greenhouse gases. Warmer seas take up more space than colder seas. Picture: AP MELTING: Nasa says global warming is responsible for sea level rise in two ways: first because warmer air increases the rate of glacial melting and, second, because the ocean is absorbing most of the extra heat trapped by greenhouse gases. Warmer seas take up more space than colder seas. Picture: AP
Environment Writer
GREENLAND’S glaciers are melting at a rate of a few metres a day during summer and researchers say the total meltwater from Greenland could cause an eventual sea level rise of 7m.
Nasa said yesterday that more than 90 percent of the planet’s freshwater ice was bound up in Greenland and the Antarctic.
With global warming, meltwaters from this ice led to rising sea levels.
“All by itself, Greenland could bump up sea levels by 7m if its ice melted completely. And it’s melting,” Nasa said.
One of the reasons for the rapid thaw of Greenland’s glaciers lies in the depth of the glaciers in a warming ocean.
A University of California glaciologist, Eric Rignot, working with Nasa’s Jet Propulsion Laboratory, led a team of researchers to Greenland in August 2014 to map the ice of three glaciers. They found that the glaciers flowing into the ocean were grounded deeper below sea level than previously thought.
Rignot said in a statement that the significance of this was that the real ocean heat was at a depth of 350 to 400m and deeper.
“In polar regions, the upper layers of ocean water are cold and fresh, and cold water is less effective at melting ice,” Rignot said.
“At a depth of 350 to 400m, this warm, salty water, of subtropical origin, melts the ice much more rapidly.”
The team also found that some of Greenland’s glaciers balanced on huge earth sills underwater, which protected them for the time being. But other glaciers, not grounded on sills, were being severely undercut by the warmer ocean at a level that was out of sight from the surface.
This undercutting meant that the glaciers could collapse and melt far sooner.
Nasa has launched a five-year project, Ocean Melting Greenland – known as OMG – which takes the investigation further, examining the four corners of Greenland from the air and from ships.
Rignot, whose results have been accepted for publication in the journal Geophysical Research Letters, said he hoped the data the project collected could be a game-changer for studying the interaction between ice and the ocean in Greenland, and help modellers make better projections of its ice sheet melting.
Nasa says global warming is responsible for sea level rise in two ways: first because warmer air increases the rate of glacial melting and, second, because the ocean is absorbing most of the extra heat trapped by greenhouse gases. Warmer seas take up more space than colder seas.
The amount of carbon dioxide absorbed by the upper layer of the world’s oceans is increasing by about two billion tons a year.
Sea levels rose about 17cm last century, but the rate in just the last decade was nearly double that.
July was the hottest month recorded globally since records by the US National Ocean and Atmospheric Administration (NOAA) began in 1880.