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VENbyAustralianstandards,lastsummer tornadoes combined. By some estimates, the close in July 2015 with the conjunction
wasascorcher.January2017wasthe 2003 heatwave centred on France killed over of 50 per cent humidity and 46°C. But it is
EhottesteverrecordedinSydneyand 70,000. Another that struck Moscow in 2010 only a matter of time.
Brisbane,andgreatswathesofthesouth-east resulted in 10,000 deaths. “Both temperature and humidity are
enduredtemperaturesthatoftenexceeded In October, The Lancet published a report going up,” says Steven Sherwood, an
40°Cforweeksonend.InSouthAustralia, featuring research by 26 global institutions atmospheric scientist at UNSW. The highest
soaringelectricitydemandcausedanoutage including the World Health Organization and risk is in places that are already humid, such
thatleft90,000homesswelteringthrougha World Bank, which concluded that we face as the Amazon, the Indus valley and many
blackoutwithnoairconditioning.AcrossNew a“looming public health emergency”. This tropical countries.“It only takes a 6°C to 7°C
SouthWales,87bushfiresblazed.Itwassohot came hot on the heels of research looking increase in temperature before some of
thatdairycowsdroppeddeadinthefields. specifically at“lethal heat”. Already, 30 per theseregions become physically uninhabitable,”
This kind of heatwave isn’t a blip. It is part cent of the world’s population experiences says Sherwood. He calculates that, unless we
of a trend that saw Sydney’s temperature potentially deadly temperatures for at least drastically reduce global warming, some
climb to over 47°C earlier this month – the 20 days every year. A team led by Camilo Mora regions will exceed this limit in 100 to
highest recorded in the city for 79 years – and at the University of Hawaii in Manoa reported 200 years.
could see both it and Melbourne experiencing in June that this will rise to nearly 75 per cent This may even be an underestimate.
mega-heatwaves with highs of 50°C by 2040. Research published in August 2017 showed
“Going out to 40 or 50 years, basically the “The 2003 heatwave that parts of India, Pakistan and Bangladesh
summer we just had will be normal,”says could occasionally exceed a wet bulb
Sarah Perkins-Kirkpatrick at the Climate centred on France killed temperature of 35°C by the end of this century.
Change Research Centre of the University This region is home to 1.5 billion people,
of New South Wales (UNSW) in Sydney. over 70,000 people” Zabout a fifth of the world’s population,
“It hasn’t really sunken in yet in Australia.” most of whom are poor and exposed to the
Australians are not alone: most of us fail by 2100 if we do little to limit greenhouse full force of lethal heat. Subsistence farmers
to take the“warming”in global warming gas emissions. So how hot is too hot? will be disproportionately affected by crop
seriously. If you live somewhere temperate, What matters is not the air temperature, failures. Yields of wheat, rice and maize –
you might even welcome a rise of a few but the temperature you experience. You can which together with soy generate nearly two-
degrees as offering more opportunity for survive for a while at well above 50°C, as long thirds of all calories consumed by people– are
picnics, barbecues and relaxed afternoons as you can sweat effectively. The problem is forecast to fall by between 3 and 7 per cent for
in pub gardens. That is unwise. Even humidity.“The only way you lose heat when each 1°C rise in global temperatures. And,
now, heatwaves are deadly, and as global you sweat is by turning liquid into vapour. in a double whammy, rising temperatures
warming increases so will the death rate. It has to evaporate,”says Graham Bates at also impact the productivity of rural
Human physiology is not designed to cope Curtin University in Western Australia.“With labourers. Since 2000, global warming has
with the temperatures predicted for large a humidity of 90 per cent, the air is almost effectively reduced the workforce in India by
swathes of the globe and many areas could saturated, and when you sweat it just drips 418,000, according to The Lancet report.
become uninhabitable. Fortunately, there off, and you won’t lose heat.” What’s more, even temperatures below
are things we can do to make our bodies The combined effect of heat and the theorised limit for human survival could
and our environments better adapted to humidity, otherwise known as the apparent render places uninhabitable, and we will reach
a warming world. temperature,canbegaugedusinga“sweating” this long before the end of the century. In fact,
With a few notable exceptions, we are thermometer: one wrapped in a damp cloth. the US National Weather Service classifies any
wet bulb temperature above 31°C as “extreme
A“wet bulb temperature”of 35°C – equivalent
SIRICHAI RAKSUE/ALAMY STOCK PHOTO consequences, so it is somewhat surprising 100 per cent humidity or 40°C and 75 per cent own heat. At rest, it generates some 100 watts,
all aware that anthropogenic warming
has widespread and sometimes severe
to an ambient temperature of 35°C and
danger”. That’s because your body produces its
about the same as a small incandescent light
humidity – is considered the limit for human
that we are only just waking up to the fact
bulb. During brief bursts of intense exercise,
survival. Above this, even a healthy person
that it can kill us. This oversight doesn’t stem
such as running, however, it can produce
in the shade won’t live longer than 6 hours.
from lack of evidence. In the US, extreme heat
more than 1000 watts, equivalent to the heat
caused more fatalities between 1978 and 2003
Nowhere on earth has experienced it yet,
although Bandar Mahshahr in Iran got very
than earthquakes, hurricanes, floods and
produced by a microwave oven. “Muscles in >
20 January 2018 | NewScientist | 37