New Zealand’s glaciers are shrinking and twelve of the largest glaciers in the Southern Alps are unlikely to return to their earlier lengths without extraordinary cooling of the climate, according to new research.

Research released by the National Institute of Water & Atmospheric Research (NIWA) today shows that the volume of ice in the Southern Alps has reduced by about 5.8 cubic kilometres, or almost 11 per cent, in the past 20 years. More than 90 per cent of this loss is from 12 of the largest glaciers in response to rising temperatures over the 20th century.

The overall shrinkage is despite almost no change in the position of the ‘End of Summer Snowline’ at the top of the Southern Alps glaciers recorded in NIWA’s latest aerial survey.

The shrinkage is occurring further down on the trunks of the bigger glaciers which have been lowering for over a century. These have now passed a threshold, where the ice is collapsing, rapidly expanding lakes at the foot of the glaciers. The shrinkage is creating some spectacular ice cliffs that are calving into the lakes.

“With future warming, significant melting of the glaciers is likely to continue,” says NIWA Principal Scientist Dr Jim Salinger.

“The twelve big glaciers with these pro-glacial lakes have passed a ‘tipping point’. It is not yet clear whether the glaciers will disappear completely with future warming, but they are set to shrink further as they adjust to today’s climate. And it is already clear that they will not return to their earlier lengths without extraordinary cooling of the climate because the large lakes now block their advance.”

The twelve glaciers are: Tasman, Godley, Murchison, Classen, Mueller, Hooker, Ramsay, Volta/Therma, La Perouse, Balfour, Grey, and Maud.

In comparison, New Zealand’s smaller glaciers, especially those west of the Main Divide, are somewhat unusual because they have their source in areas of extremely high precipitation. So, for instance, these glaciers advanced during most of the 1980s and 1990s when the area experienced about a 15% increase in precipitation, associated with more El Niño events. In most of the rest of the world (with the exception of parts of Norway), glaciers tend to be in areas of lower precipitation, so rising temperatures are affecting the glaciers there more directly and sooner.

“The iconic Franz Josef glacier is still much shorter now than in 1900,” says Dr Salinger. “Franz Josef glacier retreated about 400 metres from 2000–2005, then advanced 170 metres to 2007, but this recent gain does not compensate for the large overall losses seen over the past century.”