Glaciers are disappearing globally faster than at any time since records began 100 years ago. Most of those in central Asia could be gone by 2050.

The Celestial mountains of central Asia, the Tien Shan range, are thought to be where apples originated. But they have lost 27 per cent of their glacier mass since 1961, thanks to rising summer temperatures, and could lose a further half of what remains by 2050, according to research by Daniel Farinotti of the Swiss Federal Institute for Forest, Snow and Landscape Research in Birmensdorf, Switzerland.

Because meltwater from the glaciers supplies the Fergana Valley, one of the largest irrigated areas on earth, the impact on farmers could be immense. The snow and glacier melt from Tien Shan also provides water to northern China, Kazakhstan, Uzbekistan, Turkmenistan and Kyrgyzstan. “It’s like a huge water tower,” says Farinotti.

 Dramatic drop

The melt there is four times the global average, but rapid melting is no exception. Another study published earlier this month, which looked at the fate of all glaciers over the past century, excluding the troubled Greenland and Antarctic Ice sheets, which are affected by different dynamics, paints an equally gloomy picture.

“The first decade of the 21st century, from 2000 to 2010, saw the greatest decadal loss of glacier ice ever measured,” says lead author Michael Zemp of the World Glacier Monitoring Service at the University of Zurich, Switzerland. “It’s without precedent.”

The analysis relied on 45,000 observations taken since 1894 of 2000 glaciers. Alarmingly, it shows that in the decade from 2001 to 2010, they lost on average 75 centimetres of their thickness each year.

This rate was twice the rate in the 1990s and treble that in the 1980s, demonstrating that the losses are accelerating fast.

“It means that globally, we’re now losing treble the total ice volume of the European Alps each year,” says Zemp. “We were shocked.”

The largest retreats were seen in the European Alps, Alaska and the north-western areas of the US and Canada.

Zemp says that although the central Asian mountain study is more localised, it has tremendous value in validating the estimates and conclusions of the global study, which also found a prominent loss of ice in that area.

“It’s perfect timing that our two studies have come out at the same time,” says Zemp. “It gives us confidence that we can safely apply such measurements to all glaciers.”

Farinotti used ground and meteorological data going back to 1961, and two types of satellite data between 2003 and 2009.

One type of satellite data relied on changes in gravity that depend on the mass of the glaciers, and the other relied on measuring the distance between the satellite and the surface of the glacier. When Farinotti compared the three methods, the estimates they gave of annual ice loss were remarkably close, averaging out at 5.4 gigatonnes per year.

The upshot is that the estimates of global glacier retreat, which mainly use historical ground data of ice thickness are likely to be accurate too, says Zemp. “They confirm at a regional level what we found at global level,” he says.

The gloomiest news of all, says Farinotti, is that even if we halted emissions of carbon dioxide tomorrow, the glaciers would continue to melt for several decades because of the carbon dioxide already in the atmosphere.

Journal references: Nature Geoscience, DOI: 10.1038/ngeo2513; Journal of Glaciology, DOI: 10.3189/2015JoG15J017

Source : newscientist.com