Melting mountain glaciers are making sea levels rise faster now than at any time in the last 350 years, according to new research. Some mountain glaciers are melting up to 100 times faster than at any time in the past 350 years.
The findings, based on a new ice loss calculation technique developed by studying the glaciers of Patagonia in South America, have worrying implications for crop irrigation and water supplies around the world. The quantity of ice lost from Patagonia is equivalent to a fifth more than the contents of Lake Erie, one of the Great Lakes of North America.
Scientists behind the discovery claim their findings show that the rate of melting at the start of the 20th century was much slower than previously calculated, but that over the past 30 years it has been significantly faster than suspected. Universities at Aberystwyth, Exeter and Stockholm looked at longer timescales than usual for their study. They mapped changes in 270 of the largest glaciers between Chile and Argentina since the "Little Ice Age".
Studies showed glaciers have lost volume on average "10 to 100 times faster" in the last 30 years. The rapid melt rate is linked to their contribution to global sea level.
The new research was published in the journal Nature Geoscience on Sunday.
The glaciers straddle the Andes, on the border between Chile and Argentina. The northern icefield extends for nearly 200 km and covers a surface of 4,200 square km, while the southern icefield is more than 350km long, covering 13,000 square km.
Using the spread of moraines – the debris left by glaciers and the trim lines on mountainsides where the vegetation starts (effectively the high-tide mark of glaciers), a team led by Professor Neil Glasser of Aberystwyth University was able to compile a complicated series of calculations to work out the volume of ice that has disappeared.
Their survey centered on remotely sensed images of outlet glaciers of the south and north Patagonian ice fields, but used longer timescales than previous studies.
Since the Little Ice Age ended in Patagonia 350 years ago – they concluded – the 270 glaciers that now cover an area of at least one square
kilometer have lost 606 cubic kilometers of ice and perhaps another 123 cubic kilometers. It is the first time the historic volume of water lost from melting glaciers has been calculated accurately so far back in time. It relies on three-dimensional calculations of each glacier at its peak. The figures show the contribution to sea level rise is increasing, though still at a low level, but what alarmed the team most was that the rate of loss has sped up rapidly since 1980.
"The glaciers have lost a lot less ice up until 30 years ago than had been thought. The real killer is that the rate of loss has gone up 100 times above the long-term average. It's scary," said Professor Glasser, who carried out the study with the University of Exeter and Stockholm University. He pointed out the glaciers are at the same latitude in the southern hemisphere as the Alps are in the northern hemisphere. These are also known to be retreating and he suggested it is quite likely they are losing ice more rapidly than was thought: "If we looked at them, I'm pretty sure we would find they are also speeding up their loss rate."
Mountain glaciers are relied on around the world, but research suggests that, globally, they are losing mass and speeding up. In a few places some are increasing in mass due to higher precipitation. The calculations in Patagonia allowed the team to estimate sea level rises over more than three centuries.
"We knew that glaciers in South America were much bigger during the Little Ice Age so we mapped the extent of the glaciers at that time and calculated how much ice has been lost by the retreat and thinning of the glaciers."
Their calculations showed that in recent years the mountain glaciers have rapidly increased their melt rate and thus their contribution to global sea level.
Dr Stephen Harrison of the University of Exeter, added: "The work is significant because it is the first time anyone has made a direct estimate of the sea-level contribution from glaciers since the peak of the industrial revolution (between 1750-1850). "
BBC,"Glaciers in Chile 'melt at fastest rate in 350 years'",accessed April 5, 2011
The Independent, "Glaciers melting at fastest rate in 350 years, study finds", accessed April 5, 2011