Tropics
in trouble as rising heat, humidity push populations to the edge:
study
SMH,
20
June, 2017
Rising temperatures and
humidity will make the world's tropics increasingly unliveable by
pushing more people to the thresholds of their physical tolerance and
beyond, a new international study finds.
As
of 2000, about 30 per cent of the world's population lived in
regions where the climate exceeds deadly threshold levels – based
on temperature and relatively humidity levels – for at least 20
days a year, researchers publishing in the Nature
Climate Change journal estimate.
Earth's killer heat will get worse
A
new global study says deadly heat waves will grow in frequency,
intensity and duration, affecting 75 per cent of the world's
population if greenhouse emissions are not reduced.
Even with the most
optimistic scenario for greenhouse gas emissions reductions, that
share will rise to about 48 per cent by the end of the century. If
so-called business as usual emissions continue, that share would
climb to 74 per cent by then, the paper found.
"You are going to
have all of those people in the tropics 'cooking' there because they
are not going to have any possibility to cope with this [increase in
heat and humidity]," said Camilo Mora, the paper's
lead author and an associate professor in the Department of
Geography at the University of Hawaii, Mano.
The research examined
studies of 783 cases of excessive human deaths from heatwaves between
1980 and 2014. These included the 70,000 deaths from a huge
European heatwave in 2003 and more than 10,000 deaths in Russia in
2010.
Professor Mora noted that
identifying heatwave mortality rates was difficult because the causes
– such as heart attacks and other organ failure – may only
surface some time after the event.
"I think there is a
huge underestimate of that even in developed countries," such as
in Europe, North America and Australia, he said. For developing
nations with poorer record keeping, the deaths could be larger still.
Even
though tropical areas, including northern Australia, were not
projected to warm as much as regions further from the equator,
conditions are already near tolerance levels with further warming
forecast.
"For
many of these tropical places, the whole year becomes a heatwave,"
he said.
Air-conditioning offered
some relief but would make people "prisoners of their own homes"
– so long as electricity supplies didn't fail, Professor Mora said.
;
People
cool off in a spray from a broken water pipe during a heat wave in
Karachi, Pakistan last month. Photo:
AP
Sophie Lewis, a heatwave
specialist at the ARC Centre of Excellence for Climate System
Science, said the study highlighted how poorer populations in
particular were going to struggle.
"If we're seeing an
increase of 100 days a year that might be deadly in places that rely
on subsistence agriculture, it's going to be pretty hard for people
to be outside working," Dr Lewis said.
The
paper provided an
interactive graphic that
estimated the populations most at risk under different emissions
scenarios.
The chart [below] shows
the risks under the most ambitious scenario of cuts out to
2100, based on the so-called 2.6 representative
concentration pathway (RCP).
At the highest pollution
scenario, the RCP8.5 pathway, most of the world's tropics face high
risks by the end of the century.
(See chart below.)
The heatwave report comes
as much of south-western US faces a severe heatwave in coming days,
particularly California and Arizona.
For populations at higher
latitudes – such as Perth, Adelaide, Melbourne and Sydney –
humidity levels may decline with future warming but those gains
would be at least partly reversed by rising temperatures.
Soils, for instance, are
becoming drier in those regions, reducing the moisture available for
evaporative cooling, Professor Mora said. The process works much
like a human loses heat through sweating.
"Unfortunately the
mid-latitudes are drying out so much, the energy is retained
there like a rechargeable battery," he said
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