Three of the planet’s four great continental ice sheets are melting at an accelerating rate. More than 225 cubic kilometres of ice have disappeared in the process, adding more than a centimetre to global sea levels since 1992.
An international study published yesterday removes all doubt about the accelerating meltdown of the ice sitting atop Antarctica and Greenland, according to those involved. It ends 20 years of contradictory evidence about whether the ice sheets were growing or shrinking.
Almost 50 researchers from 26 laboratories analysed observations from 10 different satellite missions to deliver the first consistent measurement of polar ice sheet changes. “We are able to measure this much more accurately now,” joint lead researcher Prof Andrew Shepherd of the University of Leeds told The Irish Times.
The new estimates for ice loss are more than twice as accurate as previous attempts, he said. And the ice losses revealed are staggering. The Greenland ice sheet has lost about 152 billion tonnes of ice over the past two decades.
“Greenland is now losing five times more ice than it was 20 years ago. People will be concerned about that,” Prof Shepherd said.
The research team estimates that the West Antarctic sheet has lost 65 cubic kilometres of ice and the Antarctic peninsula another 20 cubic kilometres of ice. Only the East Antarctic ice sheet has shown signs of growth, adding about 14 cubic kilometres of ice since 1992, the researchers found. This is nowhere near being able to offset the overall loss of ice however, producing meltwater that adds to rising sea levels.
It is difficult to conceive of a cubic kilometre of ice, but picture a huge block covering most of central Dublin to a height almost 17 times that of Liberty Hall.
The research paper, published this morning in the journal Science, does not attribute blame for the losses but the processes affecting the ice are clear, Prof Shepherd said.
The West Antarctic ice sheet is melting faster because of warmer seas but also because of faster ice flow from the land into the sea caused by melting where the ice meets the ocean. The Antarctic peninsula and Greenland both have this faster flow but also increased ice melting from their surfaces.
The East Antarctic ice sheet is growing because of increased snowfall in the region, again caused by increased water temperatures there, Prof Shepherd said. These effects are all associated with rising global air and ocean temperatures.
Together the ice losses are three times faster than in the early 1990s and the resultant meltwater is raising sea levels by almost a millimetre a year.
Over just a few decades this is enough to increase the risk of storm-driven flooding in many coastal cities and towns, including Dublin and Cork.
