The terrible disaster in Nepal isn鈥檛 a one-off event, but a harbinger of things to come. There will be more catastrophes of this kind as mountainous regions around the world continue to warm fast, researchers warn.
鈥淚n coming years, we can expect more of these events happening,鈥� says at Newcastle University in the UK. 鈥淢aybe this is just a trailer.鈥�
Initial analyses suggested the cause of the flash flood in Tibet and Nepal on 26 August was the collapse of a glacier. Better satellite images now show that an entire slope collapsed, with huge amounts of rock below and around the glacier also falling.
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鈥淚t鈥檚 not just a glacier detachment; it鈥檚 like a large landslide with a glacier on top of it,鈥� says , also at Newcastle University.
The rock and ice plummeted into the valley below, leading to a catastrophic wave of water and debris that swept down the river. It is still not entirely clear where such a huge volume of flood water came from, says at the University of Calgary in Canada. But it appears the falling rock and ice landed on other ice left by retreating glaciers.
鈥淪o the ice in the valley bottom, as well as the ice on the glacier, is probably a lot of the water that we鈥檙e seeing in those videos,鈥� says Shugar.
Researchers are now discussing to what extent global heating contributed to this disaster in informal online forums. Davies, who has been studying glaciers in the area with Silwal and others, thinks climate change could have played a substantial part. 鈥淲e do know the area is warming very rapidly,鈥� she says. 鈥淧ictures from the 1970s show a much more substantial glacier.鈥�
That glacier would have helped support the rock slope down which it was flowing, so its thinning and retreat may have destabilised the slope to the extent it gave way. 鈥淭he term we use is debuttressing,鈥� says Davies.
Another factor could be the degrading of permafrost. Ice in cracks helps hold rocky slopes together, and helps glaciers stick to the surfaces they flow over. 鈥淭he permafrost acts like a glue that holds everything together,鈥� Davies says.
The glacier involved in this disaster is just one of many retreating glaciers in the region. What鈥檚 more, 鈥� it was 1.5 times higher from 2000 to 2023 than from 1964 to 2000.
The large glaciers on valley floors are relatively stable because of their size, but the smaller ones that flow down steep slopes and feed the valley glaciers are more vulnerable. In many cases, their lower parts are vanishing, disconnecting them from the valley glaciers. 鈥淲e鈥檙e seeing this really significant fragmentation, and that鈥檚 leaving lots of glaciers perched high up in the same way as this one that collapsed was,鈥� says Davies.
The fundamental problem is that the region is warming fast, at around 0.3掳C per decade compared with a global average of under 0.1掳C per decade, says Silwal. The same is happening in other mountainous regions around the world, a phenomenon called elevation-dependent warming.
There are three reasons for this, says at the University of St Andrews in the UK. Firstly, land areas in general warm faster than the seas.
The second reason is the loss of snow and ice cover. High-elevation areas are usually covered in snow, even in the tropics, which reflects the most sunlight. When warming melts snow, the darker surfaces absorb most of the sunlight, leading to yet more warming. 鈥淚t鈥檚 a positive feedback loop,鈥� says Silwal.
The third reason is more complex. As atmospheric carbon dioxide levels increase, more longwave radiation 鈥� heat 鈥� is being bounced back to Earth鈥檚 surface instead of escaping to space. Hot regions that are already radiating lots of heat have to warm only a little before the extra heat they radiate balances out the extra heat coming back down. This Planck feedback, as it is known, is why Earth would stop warming if CO2 levels stopped rising.
But cold regions aren鈥檛 close to radiating enough heat to balance out the extra heat arriving, so they warm more. 鈥淓levated regions, because they鈥檙e colder, somewhat counterintuitively warm up more rapidly,鈥� says Byrne.
The bottom line is that mountainous regions will keep warming fast for the foreseeable future, leading to many more disasters. 鈥淲e will continue to see bigger and more events in mountain ranges around the world,鈥� says Shugar. 鈥淲ill they be bigger than this one? I don鈥檛 know.鈥�
So what can be done to prevent them? 鈥淪topping emitting carbon dioxide would be the single most effective measure that we can deploy,鈥� says Davies.
Referring to the flood in Tibet and Nepal, Davies says, 鈥淚f this is something that鈥檚 been caused by warming, then this is something that we did, and therefore I wouldn鈥檛 call it a natural disaster.鈥�
In the absence of stopping CO2 emissions, an effective early warning system is needed so people can move to higher ground in time.
That is going to be expensive, and the high-income countries that are mostly responsible for climate change should pay, says Davies. 鈥淣epal has contributed very little to the climate crisis, yet is suffering a lot of consequences.鈥�
We tend to think of climate change as gradual, says Byrne, but events like the disaster in Nepal and Tibet and the recent wildfires in Europe show that very dramatic events can be triggered by gradual change. 鈥淚t鈥檚 been a very sobering summer in the context of climate change,鈥� he says.
