They are one of New Zealand’s biggest attractions. Hundreds visit the Fox and Franz Josef Glaciers each day. Scores of helicopter and light aircraft flights fly people up to see one of the great natural marvels of the South Island’s West Coast, situated in the Southern Alps and surrounded by lush temperature rainforest. But as the climate warms, the glaciers are in retreat once more and there may be a steep price to pay for it.
Anyone who has driven up the access road to the Franz Josef Glacier will know that along the several kilometres of its route, there are markers showing where the glacier has been in the past. Perhaps the most impressive is not actually a man made marker, but the terminal moraine left behind several kilometres west of Franz Josef and only really appreciated from the air. It was left behind from the last ice age when the sea level was much lower than it is now, the climate much colder and the glaciers much bigger.
As recently as 2007 the glaciers were advancing again after a sustained period of retreat. On some days the Franz Josef Glacier was pushing forward several centimetres every hour. However in 2008 that trend was reversed after particularly warm summers with little snowfall in the catchment. Glaciologists and climatologists agree that the long term outlook based on current trends is grim, with several kilometres of retreat back up the Waiho River valley likely in the next 80-100 years.
It therefore quite disturbing to know now that whereas 20 years ago most heavy precipitation events coming off the Tasman would normally fall as snow during winter, in the upper Waiho River valley they now largely fall as rain. Whereas 10 years ago heavy rainfall events of 400 millimetres in 2 days was considered substantial, earlier this year there was a Metservice warning issued for up to 700 millimetres over three days. Whereas 20-30 years ago heavy rainfall events, unless they came as part of low pressure systems moving out of the tropics, largely stopped on the West Coast and in the Canterbury high country lakes and headwaters during winter, now a 200 millimetre/24 hour rainfall warning is not out unheard of.
The changing hydrology of the glaciers pose problems for Franz Josef and Fox Glacier townships, which both sit close to the Waiho and Cook Rivers that flow out from underneath the glaciers. A changing climate does not help either. One of the problems is that heavier and bigger rainfall events mean the flood risk in both towns is increasing, particularly as the outwash fans process the large amounts of alluvium moving through the river systems. That means events such as the outbreak in March where the river flooded a large part of Franz Josef and caused millions of dollars in damage may become more frequent and sudden avulsion events causing the river to suddenly move across its bed may become more severe.
But it will be the economic impact that most New Zealanders will notice. Most visitors to Fox and Franz Josef Glaciers are now having to fly up to the glaciers instead of walking across the river bed from carparks at the end of the respective access roads. Whilst good for helicopter and light aircraft tours, these are quite expensive for the average tourist, limited in time that can be spent over the glaciers and causing concerns about increasingly crowded. The hits to the pocket may also help determine how long the average tourist spends in Fox and Franz Josef townships, which largely exist because of the existence of the glaciers.
Whether this is happening or not, is not the subject of debate any any longer. How bad it will get and how humans can deal with it is. But are we willing to acknowledge this? As yet, I am not confident we are.