Heatwaves have been increasing in frequency and duration since the 1950s in nearly every part of the world, a study has found.
Australian experts made a global assessment of the weather events and developed a new metric — cumulative heat — to show how much heat is packed into heatwaves.
They found that during its worst heatwave season in 2009, Australia experienced an additional 144°F [80°C] of cumulative heat across the country.
The most extreme seasons in the Mediterranean and Russia, however, clocked up more than 360°F [200°C] of extra cumulative heat.
The researchers studied heatwaves between 1950 and 2017, to pick out reliable, long-term trends from temporary, local variability.
‘Not only have we seen more and longer heatwaves worldwide over the past 70 years, but this trend has markedly accelerated,’ said paper author Dr Sarah Perkins-Kirkpatrick from the ARC Centre of Excellence for Climate Extremes.
In the Mediterranean, for example, the duration of heatwaves has been increasing by around two days per decade since the 1950s — but this rate increases to 6.4 days per decade when looking at the period between 1990 and 2017 alone.
Cumulative heat shows a similar acceleration, increasing globally on average by 1°C-4.5°C [1.8–8.7°F] each decade but in some places — like the Middle East and parts of Africa and South America — the trend is up to 10°C [18°F] a decade,’ Dr Perkins- Kirkpatrick added.
The team determined that certain regions of the world — including the Amazon, north-east Brazil, west Asia and the Mediterranean — are experiencing the most rapid changes in heatwave occurrence.
Other areas — like North Asia and South Australia — are also seeing significant changes, albeit at a slower rate.
Regardless of the nature of the changes, however, the team warned that vulnerable nations with less resilient infrastructures will be hardest hit by the changes.
‘Climate scientists have long forecast that a clear sign of global warming would be seen with a change in heatwaves,’ said Dr Perkins-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.’
‘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 full findings of the study were published in the journal Nature Communications.