Heatwaves are becoming more frequent around the world, a new paper reports.

A worldwide analysis of heatwave patterns on the regional level reveals that these have been increasing in length and frequency in the last 70 years. Cumulative heat — the total amount of heat in individual heatwaves and heatwave seasons — has also been increasing. This property signifies the intensity of the heatwave season and represents “the product of all seasonal heatwave days and average heatwave intensity.”

Catching some (heat) waves

“Not only have we seen more and longer heatwaves worldwide over the past 70 years, but this trend has markedly accelerated,” said lead author Dr. Sarah Perkins Kirkpatrick from the ARC Centre of Excellence for Climate Extremes in Australia.

For the study, the researchers looked at heatwave trends over multi-decade intervals between 1950-2017 and found some very telling signs.

The Mediterranean region, for example, saw an overall increase in heatwave duration of two days per decade. When looking at the 1980-2017 time frame specifically, the team found an increase in heatwave days of 6.4 days per decade. This suggests that most if not all of the increase is focused during these last decades.

Regions like the Amazon, north-east Brazil, and West Asia are also experiencing a rapid increase in heatwaves and their intensity while areas like South Australia and northern Asia are seeing a slower rate of increase.

Virtually all areas of the globe are seeing longer, hotter heatwaves more often, but every region is affected differently. For example, Australia experienced an additional 80°C of cumulative heat during its worst heatwave season, whereas western Russia logged a mighty 240 °C of extra heat during its worst season.

The longer a heatwave season is, and the more intense its temperatures, the higher this cumulative heat value will be. On a global level, cumulative heat is rising by roughly 1°C-4.5°C per decade, according to the authors. Some areas are experiencing rises of “up to 10°C a decade,” according to Kirkpatrick.

Such changes will impact the lives of all of us, but poorer countries with more fragile infrastructures are bound to be hit hardest, the team believes. Furthermore, they explain that longer, more intense, more frequent heatwaves have “long” been identified as “a clear sign of global warming“, according to Kirkpatrick.

“The dramatic region-by-region change in heatwaves we have witnessed over the past 70 years and the rapid increase in the number of these events, are unequivocal indicators that global warming is now with us and accelerating,” he adds.

“This research is just the latest piece of evidence that should act as a clarion call to policymakers that urgent action is needed now if we are to prevent the worst outcomes of global warming. The time for inaction is over.”

The paper “Increasing trends in regional heatwaves” has been published in the journal Nature.