They said that the chances of such a heat waveincreased by at least 30 times since the 19th century, before widespreademissions of planet-warming gases began. On average the heat wave is about 1degree Celsius (about 1.8 degrees Fahrenheit) hotter than a similar event wouldhave been in those preindustrial times, the researchers said.
“Climate change is a real game changer when itcomes to heat waves,” said Friederike Otto, a climate scientist at ImperialCollege London. “It’s really a major factor.” Otto is an author of a report onthe heat wave by World Weather Attribution, a collaborative effort amongscientists to examine extreme weather events for the influence, or lackthereof, of climate change.
The relentless heat, with temperatures soaringbeyond 100 degrees Fahrenheit for days, particularly in northwestern India andsoutheastern Pakistan, has killed at least 90 people, led to flooding fromglacial melting in the Himalayas, contributed to power shortages and stuntedIndia’s wheat crop, helping to fuel an emerging global food crisis.
The study found that a heat wave like this onenow has about a 1 in 100 chance of occurring in any given year. Before warmingbegan, the chances would have been at least about 1 in 3,000. And the chanceswould increase to as much as 1 in 5, the researchers said, if the world reaches2 degrees Celsius of warming, as it is on track to do unless nations sharplyreduce emissions. The world has already warmed about 1.1 degrees Celsius sincethe late 19th century.
South Asia is no stranger to heat this time ofyear, but this heat wave began early, near the beginning of March, and iscontinuing in some areas where little relief is expected until monsoon rainsarrive in the next few months.
The scientists analysed maximum dailytemperatures for March and April, and used computer simulations of the world asit is now and of a fictional world where emissions, and warming, neveroccurred. While this study has not been peer reviewed, these model-comparisontechniques have been peer-reviewed in the past and are now widely used andaccepted.
Because of the lack of a long observationalrecord and other uncertainties, the researchers said, the findings areconservative, and the chances of such an event are likely more than 30 timesgreater than they were before warming began.
The analysis also looked at the effects of theprolonged heat. Arpita Mondal, a climate scientist at the Indian Institute ofTechnology Bombay in Mumbai and an author of the study, said gathering dataabout the effects on wheat, a crop that is sensitive to extreme heat, wasdifficult, despite anecdotal reports of damage.
“But what has been quite startling is thatIndia has banned its wheat exports to the rest of the world,” she said. “Thatin itself is evidence enough that our agricultural productivity has beenaffected.”
The ban, coupled with the effects of theRussian invasion of Ukraine on wheat exports from there, has internationalagencies concerned about the potential of a global food shortage.
Another author, Roop Singh, a climate riskadviser with the Red Cross Red Crescent Climate Center, said that, like otherheat waves, this one shows that the effects tend to fall disproportionately onthe poor.
She said there have been reports of widespreadpower outages, in part because the need for more cooling strains the system,and in part because of a coal shortage in India. “This is particularlyimpactful for the poorest people who might have access to a fan or to a cooler,but might not be able to run it because they can’t afford a generator,” shesaid.
The findings of the study are consistent withmany other analyses of similar events over the past two decades, including anextraordinary heat wave last summer in the Pacific Northwest and WesternCanada. This field of research, called attribution analysis, has contributed toa growing understanding among scientists and the public that the damagingeffects of global warming are not some far-off problem but are alreadyoccurring.
Because emissions have raised the world’sbaseline temperature, the link between heat waves and climate change isespecially clear. Otto said that in studies of other extreme events like floodsor drought, climate change is usually only one factor among several.
In a recent paper, Otto and others argued thatthe influence of global warming on heat waves is now so apparent that it is“fast becoming an obsolete question.” The “next frontier” for attributionscience, they wrote, is to provide information to help people decide how toadapt to extreme heat.
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