Heat waves have increased both in length and in frequency in almost every part of the world since the 1950s, according to what is described as the first study to examine the problem regionally.
The study found that the escalation of heat waves varied across the planet, with the Amazon, northeastern Brazil, western Asia (including parts of the subcontinent and central Asia) and the Mediterranean, all experiencing a faster change than, for example, southern Australia and northern 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 growing trend in the total number of days of heat waves within and between regions and that heat waves were lengthening in the past 70 years.
The only measure related to heat waves that had not increased on a global scale was the average intensity, which is the average temperature of all heat waves per season. The only places where they increased were southern Australia and parts of Africa and South America.
But the research also looked at a new measure known as cumulative heat – or cumulative intensity – which evaluated the amount of additional heat present in a single extreme heat event beyond the traditional threshold that defined the beginning of a heat wave .
It turned out that the amount of cumulative intensity in the heat wave seasons has increased across the planet and over the decades. The average increase per decade was between 1 ° C and 4.5 ° C (an increase between 1.8 ° F and 8.1 ° F), although in some places – the Middle East and parts of Africa and South America – the rise was closer to 10 ° C a decade.
Sarah Perkins-Kirkpatrick, of the Australian Center of Excellence of the Research Council for Climate Extremes and lead author of the study, said that not only have there been increasingly long heat waves worldwide over the past 70 years, but the trend is greatly accelerated.
He 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 have been a “call for clarification” for policy makers who urgent action was needed to prevent the worst impacts of the climate crisis.
“The time for inaction is over,” said Perkins-Kirkpatrick. “The dramatic change region by region in the heat waves we have witnessed and the rapid increase in the number of these events are unequivocal indicators that global warming is with us and is accelerating.”
The worst recorded heat waves regularly align with catastrophic events. In southeastern Australia, the worst heat wave season was the summer of 2009, when about 374 people died in three days from the extreme heat and, two weeks later, the black Saturday fires killed 173 people.
The most severe heat wave that hit the Mediterranean was in the summer of 2003, when it was estimated that there were 70,000 excess deaths in Europe due to the extreme heat which also caused damage of over 13.1 billion euros (£ 11.8 billion) to agriculture and forests.