They said that the chances of such a heat wave
increased by at least 30 times since the 19th century, before widespread
emissions of planet-warming gases began. On average the heat wave is about 1
degree Celsius (about 1.8 degrees Fahrenheit) hotter than a similar event would
have been in those preindustrial times, the researchers said. “Climate change is a real game changer when it
comes to heat waves,” said Friederike Otto, a climate scientist at Imperial
College London. “It’s really a major factor.” Otto is an author of a report on
the heat wave by World Weather Attribution, a collaborative effort among
scientists to examine extreme weather events for the influence, or lack
thereof, of climate change. The relentless heat, with temperatures soaring
beyond 100 degrees Fahrenheit for days, particularly in northwestern India and
southeastern Pakistan, has killed at least 90 people, led to flooding from
glacial melting in the Himalayas, contributed to power shortages and stunted
India’s wheat crop, helping to fuel an emerging global food crisis. The study found that a heat wave like this one
now has about a 1 in 100 chance of occurring in any given year. Before warming
began, the chances would have been at least about 1 in 3,000. And the chances
would increase to as much as 1 in 5, the researchers said, if the world reaches
2 degrees Celsius of warming, as it is on track to do unless nations sharply
reduce emissions. The world has already warmed about 1.1 degrees Celsius since
the late 19th century. South Asia is no stranger to heat this time of
year, but this heat wave began early, near the beginning of March, and is
continuing in some areas where little relief is expected until monsoon rains
arrive in the next few months. The scientists analysed maximum daily
temperatures for March and April, and used computer simulations of the world as
it is now and of a fictional world where emissions, and warming, never
occurred. While this study has not been peer reviewed, these model-comparison
techniques have been peer-reviewed in the past and are now widely used and
accepted. Because of the lack of a long observational
record and other uncertainties, the researchers said, the findings are
conservative, and the chances of such an event are likely more than 30 times
greater than they were before warming began. The analysis also looked at the effects of the
prolonged heat. Arpita Mondal, a climate scientist at the Indian Institute of
Technology Bombay in Mumbai and an author of the study, said gathering data
about the effects on wheat, a crop that is sensitive to extreme heat, was
difficult, despite anecdotal reports of damage. “But what has been quite startling is that
India has banned its wheat exports to the rest of the world,” she said. “That
in itself is evidence enough that our agricultural productivity has been
affected.” The ban, coupled with the effects of the
Russian invasion of Ukraine on wheat exports from there, has international
agencies concerned about the potential of a global food shortage. Another author, Roop Singh, a climate risk
adviser with the Red Cross Red Crescent Climate Center, said that, like other
heat waves, this one shows that the effects tend to fall disproportionately on
the poor. She said there have been reports of widespread
power outages, in part because the need for more cooling strains the system,
and in part because of a coal shortage in India. “This is particularly
impactful 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,” she
said. The findings of the study are consistent with
many other analyses of similar events over the past two decades, including an
extraordinary heat wave last summer in the Pacific Northwest and Western
Canada. This field of research, called attribution analysis, has contributed to
a growing understanding among scientists and the public that the damaging
effects of global warming are not some far-off problem but are already
occurring. Because emissions have raised the world’s
baseline temperature, the link between heat waves and climate change is
especially clear. Otto said that in studies of other extreme events like floods
or drought, climate change is usually only one factor among several. In a recent paper, Otto and others argued that
the influence of global warming on heat waves is now so apparent that it is
“fast becoming an obsolete question.” The “next frontier” for attribution
science, they wrote, is to provide information to help people decide how to
adapt to extreme heat. ©2022 The New York Times Company