Heatwave trends accelerate worldwide
Frequency, duration and new metric cumulative heat reveals rapid rise in heatwave impacts

Date:
July 6, 2020
Source:
University of New South Wales
Summary:
The first comprehensive worldwide assessment of heatwaves down
to regional levels has revealed that in nearly every part of the
world heatwaves have been increasing in frequency and duration
since the 1950's. The research has also produced a new metric,
cumulative heat, which reveals exactly how much heat is packed
into individual heatwaves and heatwave seasons. As expected,
that number is also on the rise.



FULL STORY ==========================================================================
The first comprehensive worldwide assessment of heatwaves down to
regional levels has revealed that in nearly every part of the world
heatwaves have been increasing in frequency and duration since the 1950s.


==========================================================================
The research published in Nature Communications has also produced a new
metric, cumulative heat, which reveals exactly how much heat is packed
into individual heatwaves and heatwave seasons. As expected, that number
is also on the rise.

In Australia's worst heatwave season, an additional 80DEGC of cumulative
heat was experienced across the country. In Russia and the Mediterranean,
their most extreme seasons baked in an additional 200DEGC or more.

"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.

"Cumulative heat shows a similar acceleration, increasing globally on
average by 1DEGC-4.5DEGC each decade but in some places, like the Middle
East, and parts of Africa and South America, the trend is up to 10DEGC
a decade." The only heatwave metric that hasn't seen an acceleration
is heatwave intensity, which measures the average temperature across
heatwaves. This is because globally we see more heatwave days and
heatwaves are lasting longer.

When the average temperature is measured across longer heatwaves any
shifts in intensity are almost undetectable. Only southern Australia
and small areas of Africa and South America show a detectable increase
in average heatwave intensity.

The study also identified that natural variability impacts on heatwaves
can be large at regional levels. This variability can overwhelm heatwave trends, so regional trends shorter than a few decades are generally not reliable. To detect robust trend changes, the researchers looked at how
the trends had changed over multi-decade intervals between 1950-2017. The changes were stark.

For example, the Mediterranean, saw a dramatic uptick in heatwaves when measured over multi-decade spans. From 1950-2017, the Mediterranean saw
an increase in heatwaves by two days a decade. But the trend from 1980
to 2017 had seen that accelerate to 6.4 days a decade.

The regional approach also showed how the trends vary. Regions like
the Amazon, north-east Brazil, west Asia and the Mediterranean are
experiencing rapid changes in heatwaves while areas like South Australia
and North Asia are still seeing changes but at a slower rate.

However, no matter whether these changes are rapid or slow, it seems
inevitable that vulnerable nations with less infrastructure will be hit
hardest by extreme heat. "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."

========================================================================== Story Source: Materials provided by
University_of_New_South_Wales. Original written by Alvin Stone. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. S. E. Perkins-Kirkpatrick, S. C. Lewis. Increasing trends in
regional
heatwaves. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020- 16970-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200706114005.htm

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