Heat waves have increased in both length and frequency in almost all parts of the world since the 1950s, according to what is described as the first study to analyze the problem at the regional level.
The study found that heat wave escalation varied across the planet, with the Amazon, Northeast Brazil, Western Asia (including parts of the subcontinent and Central Asia), and the Mediterranean, all experiencing faster change than eg South Australia and North Asia. The only inhabited region where there was no trend was in the central United States.
Published in the journal Nature Communications, the study found a clear upward trend in the total number of heat wave days within and across regions, and that heat waves became longer in the past 70 years.
The only measure related to heat waves that had not increased globally was the average intensity, which is the average temperature in all heat waves per season. The only places where that increased were southern Australia and parts of Africa and South America.
But the research also examined a new measure known as cumulative heat, or cumulative intensity, that assessed the amount of additional heat in an individual extreme heat event beyond the traditional threshold that defined the onset of a heat wave.
The amount of intensity accumulated in heat wave stations was found to increase across the planet and over the decades. The average increase per decade was between 1C and 4.5C (an increase of between 1.8F and 8.1F), although in some places, the Middle East and parts of Africa and South America, the increase was closer to 10C per decade.
Sarah Perkins-Kirkpatrick, from the Australian Council of Research Center for Excellence in Climate Extremes and lead author of the study, said that not only had there been more and more heat waves around the world in the past 70 years, but the trend had accelerated remarkably.
She said it was consistent with what climate scientists had long predicted, that an increase in heat waves would be a clear sign of global warming, and that the results should be a “wake-up call” to those responsible for the formulation of policies that urgent measures were needed to prevent the worst impacts of the climate crisis.
“The downtime is over,” said Perkins-Kirkpatrick. “The dramatic region-by-region change in the heat waves we’ve witnessed, and the rapid increase in the number of these events, are unequivocal indicators that global warming is with us and accelerating.”
The worst regularly recorded heat waves line up with catastrophic events. In Southeast Australia, the worst heat wave season was the summer of 2009, when an estimated 374 additional people died over three days due to extreme heat and, two weeks later, Black Saturday forest fires killed 173 people. .
The most severe heat wave to hit the Mediterranean was in the summer of 2003, when it is estimated that there were 70,000 excess deaths in Europe due to the extreme heat that also caused more than € 13.1bn (£ 11.8bn) of damage to agriculture and forests.
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