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For millennia, the high peaks of the Himalayas were held together by an invisible, frozen cement – permafrost and glacial ice that bound ancient rock into seemingly unshakable fortresses. But as the planet continues to warm, this alpine glue is liquefying.
The glacial collapse and deluge in Nepal and Tibet was not a freak weather event; it was the structural failure of a mountain itself, nature’s latest commentary on the deadly consequences of human-caused planetary warming. And it was the exclamation point on a summer of extremes, illustrating with a sole unnatural disaster the apocalyptic future that lies in store if we fail to take dramatic climate action.
As the death toll continues to mount – the latest count showed more than 900 dead and more than 4,400 individuals missing – this event has crystalized the climate crisis for many.
One reason is undoubtedly the sheer horror of what unfolded here. Chilling surveillance and eyewitness footage captured the horrific moment a 40mph wall of “liquid concrete” violently overtook fleeing crowds, instantly swallowing entire families and burying them beneath feet of thick, red-soaked silt. Another reason, however, is that the connection with climate change was unassailable in this case.
The torrent was the direct result of warming-induced glacial collapse, which dumped millions of tons of rock, unleashing a high-velocity wave of mud and debris. The new reality in the era of human-caused climate change, a CNN headline put it, is that “living downstream from a glacier has become a deadly liability”.
The impact of climate change on extreme weather, by contrast, is usually established though a statistical, rather than direct causal, connection. Through what is known as attribution science, climate scientists demonstrate the influence of climate change on the characteristics of an extreme weather event. It is analogous to how epidemiologists establish a linkage between cause (eg smoking cigarettes) and effect (lung cancer), through massive statistical evidence.
In the case of climate attribution, scientists run parallel climate model simulations, including a “control” simulation that represents a counterfactual world without human impact, and a “treatment” simulation where human drivers – primarily the increase in greenhouse gas concentrations – are included. They then compare how often a particular event happens in the two cases. If there is a substantial increase in occurrence of a particular event in the “treatment” simulation relative to the “control” simulation, then the extremeness of the event – and its human, societal or environmental impacts – can be “attributed” to climate change.
Critics might say that the connection here is merely statistical – almost circumstantial. But much as we are willing to attribute causality when a lifetime smoker contracts lung cancer because they were as much as 30 times more likely to do so because of their use of tobacco products, the extreme characteristics (unusually massive precipitation totals, high temperatures or destructive winds) of the weather event can be attributed to human-caused warming.
While the tragic and deadly Tibetan flood might have been the most prominent climate change-induced disaster this summer, it followed an unprecedented series of deadly, destructive and dangerous extreme weather events that can be connected to rising carbon pollution and the warming of our planet.
This summer of extremes began early. It started out with a March “heat dome” in the south-western US that yielded extremes of heat we only expect to see in mid-summer. The unprecedented extreme March heat was found by climate scientists to have been “virtually impossible” in the absence of human-caused warming.
Then came a midsummer-like May heat dome in the eastern US that smashed temperature records in my home city of Philadelphia. And within weeks, a European heat dome brought deadly triple-digit temperatures to large parts of France leading to the deaths of more than 3,000 people in Paris and nearly 6,000 for all of France. That was just the first of four record-breaking, back-to-back heatwaves in Europe that, by summer’s end, has cost the lives of more than 35,000 people. And yes, the deadly heat was attributed to climate change.
The record July heat combined with extreme dryness over large parts of western Europe – particularly France and Spain – to generate catastrophic wildfires that dominated the headlines for weeks, along with a viral photo of vacationers calmly lounging under a colorful umbrella while apocalyptic wildfire smoke billows in the background. The fires forced the evacuation of hundreds of thousands of people from their homes. And at the risk of sounding like a broken record: yes, it was formally attributed to human-caused warming.
Back in the US, we had our own wildfire problems. A combination of very hot and dry conditions over southern Ontario and the upper midwest led to huge wildfires generating plumes of smoke that choked the east coast for weeks. Air quality was rated hazardous in my home city of Philadelphia.
And yes, these wildfires – and indeed, the Canadian wildfires we now see summer after summer – can be attributed to climate change.
The summer of extreme weather disasters wasn’t done with us yet. In mid-August a historic “derecho” (a very wide, fast-moving line of severe thunderstorms associated typically with destructive, hurricane-strength straight-line destructive winds) struck the midwestern US with winds exceeding 100mph and devastating flooding, the better part of a million people from Illinois to Virginia were left without power.
While it is a challenge to apply attribution methods to these rare events, there is emerging evidence that climate change is making them more frequent and more damaging.
This past summer’s collective extreme weather disasters were an unmistakable consequence of the continued warming of our planet. The current administration’s policies – which were written by polluters themselves – are making things worse. Donald Trump and enabling congressional Republicans continue to double down on policies favoring fossil fuel extraction and dependence at the very time we need to be moving even more quickly away from fossil fuels toward clean energy.
These extreme events underscore the urgency of taking action now, and – while there are many things we can do – one of the greatest opportunities Americans will have to affect climate policy is the upcoming midterm election. You can make support for urgent and dramatic climate action a litmus test issue as you go to the voting booth.
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Michael Mann is presidential distinguished professor and director of the Penn Center for Science, Sustainability and the Media at the University of Pennsylvania, and co-author with Peter Hotez, of the recent book Science Under Siege
