Deadly South Asia heatwave a once-in-3,000-year event before climate change, experts say
- The heatwave, which has claimed at least 90 lives across India and Pakistan in recent months, was made 30 times more likely by climate change, scientists said
- ‘This is a sign of things to come,’ said one of the authors of the World Weather Attribution study, adding it could occur every 5 years if warming continues
Before the onset of human-caused climate change, the chances of such an event occurring would have been roughly once every 3,000 years, said senior author Friederike Otto, a scientist at Imperial College London’s Grantham Institute.
Global warming to date of 1.2 degrees Celsius (2.2 degrees Fahrenheit) has shortened the so-called return period for extreme heat of similar duration and intensity in South Asia to once-a-century, she and colleagues in the World Weather Attribution (WWA) consortium found.
But as the planet continues to heat up, the interval between such killer heatwaves will shrink even further.
If warming increases to 2 degrees Celsius then heatwaves like this could occur twice in a century or even once every five years, said Arpita Mondal, a climate scientist at the Indian Institute of Technology in Mumbai, who was part of the study. “This is a sign of things to come,” she said.
A 2 degrees Celsius world is an unsettlingly plausible scenario: current national commitments to curb carbon pollution under the Paris Agreement would see global warming of 2.8 degrees.
“Whether today’s most impactful heatwaves could have occurred in a pre-industrial climate is fast becoming an obsolete question,” Otto said.
“The next frontier for attribution science is to inform adaptation decision-making in the face of unprecedented future heat,” she said by email.
“This means the most important aspect of our study is what it says about a 2C world.”
The March-April period was the hottest on record for that time of year in Pakistan and India.
It will be months before the full toll of lives lost and economic damage can be calculated, including hospitalisations, lost wages, missed school days, and diminished working hours.
More than 90 deaths have been directly attributed to the heatwave, but earlier hot spells over the last decade suggest that number will climb far higher, perhaps into the thousands.
One impact was immediate.
The withering heat combined with 60 to 70 per cent less rain than usual turned what promised to be a bumper wheat crop in India into an agricultural disaster.
The unprecedented duration of the heatwave, which saw power outages as temperatures soared into the high 40s, suggests climate vulnerable countries are racing against the clock to prepare for a climate-addled future, the report said.
Already today, “the limits to adaptation are being breached for a large, poor population of the region,” cautioned Islamabad-based climate scientist and co-author Fahad Saeed.
“One can imagine how bad it would be even for a 1.5C-warmer world,” he said, referring to the aspirational Paris treaty target for capping the rise in global temperatures.
Any warming beyond 1.5 degrees, he added, would pose an “existential threat” for vulnerable populations without access to air conditioning or other ways to keep cool.
The new report – which was released on Monday and calculated the average of daily maximum temperatures in March and April across a large swathe of northwestern India and southern Pakistan – may underestimate the frequency of such heatwaves, today and in the future, the authors noted.
Indeed, an assessment by Britain’s Met Office using somewhat different methods concludes that warming to date increased the likelihood of the South Asia heatwave 100-fold.
Scientists have long predicted such impacts, but only recently has more data, better models and increased computing power made it possible to calculate to what extent is a particular weather disaster is made worse by global warming.
The WWA determined, for example, that the heatwave that gripped western North America last June – sending temperatures in Canada to a record 49.6 degrees – would have been “virtually impossible” without human-induced climate change.
“As long as greenhouse gas emissions continue, events like these will become an increasingly common disaster,” said Otto.
Heatwaves, she noted, are today the deadliest of extreme weather events.
Additional reporting by Associated Press