50C Temperatures are Coming to Sydney and Melbourne

Sydney and Melbourne can expect summer days when the mercury climbs to 50 degrees Celsius within a couple of decades if greenhouse gas emissions continue to rise, new research has found.

By NICK MOIR/SMH

The study, led by Sophie Lewis at the Australian National University, analysed new models being prepared for the Intergovernmental Panel on Climate Change (IPCC) to examine the difference between a 1.5C and 2C warming limit compared with pre-industrial times.

At the upper end of the range – which would amount to a 1.1-degree rise from current global warming levels – NSW's record extremes would increase 3.8C compared with existing records. Those in Victoria would rise by 2.3C, the simulations showed.

ZAK KACZMAREK/GETTY

Fifty degree temperatures are coming for Sydney and Melbourne, all thanks to climate change.

For Sydney and Melbourne, populations could swelter in 50C weather even if the 2C global warming limit agreed in the 2015 Paris accord were achieved, according to the research co-authored by Andrew King from Melbourne University and published Wednesday in Geophysical Research Letters.

MICK TSIKAS/REUTERS

A bushfire burns through a forest near Melbourne on Black Sunday in February, 2009.

The current records for the two cities are 45.8C for Sydney, set on January 18, 2013, and 46.4C for Melbourne on Black Saturday, 7 February, 2009. Such hot days increase the risks of bushfires.

"If we warm average temperatures, we shift the whole distribution of temperatures, and we see a really large percentage increase in the extremes," Lewis said. 

"What seems like a small increase in average temperatures, say 1 degree, can lead to a two- or three-fold acceleration in the severity of the extremes."

RECORD HIGHS

Temperature records are being broken frequently in Australia, with hot records 12 times more likely to be set than cold ones since 2000,

A heatwave last month smashed many records across eastern Australia with more than half the NSW stations with more than 20 years of data registering their hottest September day, the Bureau of Meteorology said.

Under a high carbon emissions scenario, 50-degree days could arrive "as early as the 2040s", Lewis said, adding that even with a concerted reduction in pollution, those temperatures could be reached by about 2060. Dr King said hospitals, electricity systems and infrastructure would all struggle during such heat spikes.

"For summer heat extremes in the future, there probably aren't any winners," King said. 

REEFS AT RISK

Along with other Australian regions which could see 50-degree days, the researchers also examined the temperature increases in the Coral Sea.

Even with less variability than land, oceans are also seeing significant warming. For temperature-sensitive coral reefs, the past few years of ocean heatwaves has triggered mass bleaching including on the Great Barrier Reef. 

The researchers estimated autumn extremes of 0.3-0.8C above the devastating 2016 record in the Coral Sea with the lower target of the Paris accord. At the 2C warming goal, the Coral Sea will warm 0.6-1.2C above the 2016 extreme.

Lewis said the recent bleaching had "really smashed the reef", killing as much as half the Great Barrier Reef corals.

"If that's occurring now and we have additional warming on top of that - which will lead to an increase in seasonal temperatures - then that's a real worry for whether we'll have a reef at all, she said.

'STARTLING SPEED'

Dr King was also a co-author of a separate paper out recently in Environmental Research Letters that examined the impact on Europe if global temperatures reached that 2C upper limit agreed at Paris.

The paper found a heatwave of the scale of 2003 which killed 70,000 Europeans rapidly becomes more likely as the planet warms.

"What is startling is the speed of the change," Dr King said. "At 2C, events like the 2003 heatwave could become so commonplace that they occur every second year."

While trends in regional seasonal rainfall levels are less clear, a warming world is likely to make single-day extreme rainfall events more likely. In Britain's case, a repeat of the July 2007 severe flooding would be 70 per cent more likely at 2C warming compared with current conditions, he said.

 - Sydney Morning Herald

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