The great southern glacier retreat
THE advent of warm summer days around most of the country is good news for holidaymakers.
But at a time when many melt at the beach, lake or river, New Zealand’s glaciers will be taking another hammering.
The effects of a warming climate are erratic, and glaciers themselves will retreat, shrink, advance and thicken according to a mix of influences.
Overall, however, the picture is stark and discouraging. The shrivelling and disappearing of glaciers are clear signals of changing times.
Worse still is the accelerating rate. New Zealand’s ice loss in 201519 was nearly seven times that of 200004.
Only a generation or two ago New Zealand boasted how Franz Josef and Fox Glaciers flowed into the forest and close to the coast. Not any more.
Tasman Lake near AorakiMt Cook did not exist then. Now, tourists take boat trips and slices of ice regularly calve into the expanding lake.
A few months ago, another study revealed bad news for the glaciers.
University of Canterbury glaciologist Heather Purdie and a collaborator have been finding glaciers are melting faster than previously understood — from within rather than from the surface.
Air that is warmer than expected is being trapped within crevasses. While Dr Purdie has been studying the Tasman Glacier, the implication is that the amount of melting is being underestimated and the volume of remaining ice overstated.
Topographical maps show hundreds of glaciers and snowfields that no longer exist. Many a climbing route has become cut off. Many a mountain has become less stable as ice holding high places together melts.
There is no mystery as to the cause — hotter temperatures.
The year before last was New Zealand’s hottest on record, and last year began with the hottest January yet. Another hot year has been recorded for 2022.
Snow accumulates in the neve of glaciers and a slowmoving river of ice is created. There are, therefore, long lags for glacier change. Even with miracle cuts to greenhouse gas emissions, it would be decades before most glaciers could recover.
Sometimes, extra precipitation if it is cold enough can help the health of glaciers. Franz Josef advanced between 1983 and 2008 because of other weather phenomena.
But it has been going backwards fast since then. In 2021 it lost 1.56km in length.
Snow cover, less common these days, can also help maintain the ice underneath. And once bare rock is exposed, it is extremely hard for glaciers to reestablish.
University of Otago associate professor Nicolas Cullen has estimated glacier volume shrank about 35% between 1978 and 2020.
The phenomenon is, of course, worldwide. With each northern summer comes news of scorching European temperatures and of glaciers vanishing.
In New Zealand, glaciers help provide more consistent flows in summer and autumn into the southern lakes and Clutha and Waitaki Rivers.
Already, the landscape and beauty of the mountains have changed markedly. We had better, at least, enjoy what we now have. More change is rapidly on the way.