Heat wave trends accelerate around the world

The first comprehensive global assessment of heat waves at regional levels has revealed that in almost all parts of the world heat waves have increased in frequency and duration since the 1950s.

Research published in Nature’s Communications It has also produced a new cumulative metric heat, which reveals exactly how much heat accumulates in individual heat waves and heat wave seasons. As expected, that number is also on the rise.

In Australia’s worst heat wave season, an additional 80 ° C of cumulative heat was experienced across the country. In Russia and the Mediterranean, its most extreme stations were baked at 200 ° C or higher.

“Not only have we seen more and more heat waves around the world in the past 70 years, but this trend has accelerated remarkably,” said lead author Dr. Sarah Perkins Kirkpatrick of the ARC Center of Excellence for climatic extremes.

“Cumulative heat shows a similar acceleration, increasing globally on average from 1 ° C to 4.5 ° C every decade, but in some places, such as the Middle East and parts of Africa and South America, the trend is up to 10 ° C per decade. “

The only heat wave metric that has not seen an acceleration is the intensity of the heat wave, which measures the average temperature across the heat waves. This is because worldwide we see more days of heat waves and heat waves last longer. When the average temperature is measured in longer heat waves, any change in intensity is almost undetectable. Only southern Australia and small areas of Africa and South America show a detectable increase in the average intensity of heat waves.

The study also identified that the impacts of natural variability on heat waves can be large at the regional level. This variability can overwhelm heat wave trends, making regional trends of less than a few decades generally unreliable. To detect robust trend changes, the researchers looked at how trends had changed at intervals of several decades between 1950-2017. The changes were harsh.

For example, the Mediterranean experienced a dramatic rebound in heat waves when measured over periods of several decades. From 1950 to 2017, the Mediterranean experienced an increase in heat waves in two days per decade. But the trend from 1980 to 2017 had seen it accelerate to 6.4 days per decade.

The regional approach also showed how trends vary. Regions such as the Amazon, Northeast Brazil, Western Asia, and the Mediterranean are experiencing rapid changes in heat waves, while areas such as South Australia and Northern Asia are still experiencing changes, but at a more rapid rate. slow.

However, no matter if these changes are fast or slow, it seems inevitable that vulnerable nations with less infrastructure are the most affected by extreme heat.

“Climate scientists have long predicted that a clear sign of global warming would be seen with a change in heat waves,” said Dr. Perkins Kirkpatrick.

“The dramatic region-by-region change in heat waves we’ve witnessed in 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 investigation is just the latest evidence that should act as a wake-up call to policy makers that urgent action is now needed to prevent the worst results of global warming. The downtime is over.”

Provided by ARC Center of Excellence for Climate Extremes (CLEx)