Glacial retreat (and UV risk)

Not quite a case of every cloud having a silver lining ...

Next month, my wife and I will be returning home from Hanmer Springs via the scenic Haast Pass route down the stunningly beautiful (but often wet) West Coast of Te Wai Pounamu, Aotearoa (the South Island of New Zealand). We’re booked to have an overnight stay near the Fox Glacier tourist village so we can recharge the car. But we won’t bother to drive out to the face of the glacier or the nearby Franz Josef Glacier. Since I first saw them - as a child in the 1950s - they’ve become only shadows of their former selves. After a partial recovery around the turn of the century, they’re now back in full retreat, as you can see in the plot below.

What was once a short stroll from the car-park to their spectacular ice-faces is now a long hike from a car park much further up the valley.

Here’s a before-and-after image of the Franz Josef Glacier from a 2021 article in the Guardian. I find it rather depressing.

The photo at left was taken in 1871, and the one at right was from the same point in 2016 (before most of the rapid retreat of the last decade). The Guardian article includes several great interactive time-lapse views too. Well worth a play.

They made extensive use of data collected by colleagues at NIWA, who’ve been monitoring changes from aircraft surveys since the 1970s. This new video below, from those NIWA colleagues, gives an updated flavour of the damage wrought there by Climate Change.

Since 1978, more than a third of all the ice in New Zealand’s glaciers has melted. They say in the clip that it’s a loss of about 13 trillion litres, which is equivalent to the household water needs of all New Zealanders during that time.

The loop adds to the even longer record captured in the historic paintings of several glaciers in Te Wai Pounamu.

Bad news. But does this have anything to do with UV, you might ask? Well, it turns out that is does. Glacier-walkers, like those pictured in the Guardian article are exposed to much higher levels of UV radiation than they’d experience at sea level. In a paper led by my colleague Martin Allen a few years ago, we showed that the UV levels at Mount Hutt ski field (altitude 2 km) were about 25 percent greater than nearby sites near sea level. About half of that difference is due to the snow-covered surface, so those retreating glaciers will eventually lead to reductions in UV exposure.

In clean air like New Zealand’s, the UV increases by only 5 or 6 percent per kilometre of elevation change, so that accounts for only half the increase we observed at the ski field. The remainder is due to the highly reflecting surface. Snow and ice are among the few natural materials that reflect a large proportion of the incoming skin-damaging UV radiation in sunlight. Once reflected, much of it is then re-scattered back towards the surface by molecules of air.

Those lower future UV doses may be tiny glimmer of better news. But I’d much rather have kept the glaciers as they were for my great grandchildren. Too late now …☹

The time to sideline the fossil fuel industry is long overdue, and (without mentioning any names) the views of its ‘champions’ should be consigned to history. Fossils belong in the ground.