Shrinking glaciers blamed on reduction in snowfall

NZ's glaciers have shrunk this year, in contrast to the previous three years when they actually grew. Picture / Gottlieb Braun-Elwert

New Zealand's glaciers shrank last summer but the retreat may have more to do with the lower snowfall than global warming.

"Much less snow fell in the Southern Alps," said National Institute of Water and Atmospheric Research senior climate scientist Jim Salinger.

The loss of ice mass last year was in contrast to the previous three years, when the glaciers actually grew.

Glaciers are affected by two climatic conditions: Snowfall, which adds to their mass during winter, and warm temperatures, which spur melting in summer. Increased anticyclone weather patterns in the six months to last Christmas produced drier and milder conditions, and temperatures above average.

"These conditions produced less snow in winter, and the warmer temperatures in spring resulted in early snowmelt," Dr Salinger said.

The annual survey of 50 glaciers by Niwa showed that snow lines in March, at the end of summer, were on average 50m higher than where they needed to be to maintain a constant supply of ice to the glaciers.

"The higher the snowline, the more snow has been lost to feed the glacier."

The heavier seasonal snowfalls this past winter - the coldest in a decade - may mean the glaciers will regain some of their mass, but much will depend on the conditions over the coming summer.

Dr Salinger said that worldwide, glaciers were regarded as a canary in the coalmine in terms of global warming.

The world's many thousands of glaciers have been stable or in slow retreat for more than 100 years, but since about 1980 most have been retreating drastically, most rapidly in the Himalayas, the Arctic, the Alps, the Rockies and the tropics.

Most glaciologists believe this is being accelerated by global warming, but Dr Salinger said the behaviour of glaciers in New Zealand was a little more complicated.

"Our glaciers - particularly those west of the main divide - are very sensitive to the rain and snow that falls as well as the temperature. Those to the west have not been retreating to the same extent as glaciers worldwide."

- NZPA