A new study from the Australian National University warns that the world needs to cut greenhouse gas emissions beyond the level of the Paris climate agreement.
A new study from the Australian National University warns that the world needs to cut greenhouse gas emissions beyond the level of the Paris climate agreement. DAVE HUNT

50-degree days inevitable: study

AUSTRALIA'S largest cities need to prepare for unprecedented extreme heat events with temperatures potentially reaching 50C in "just a few decades,” researchers say.

A new study led by the Australian National University (ANU) has warned that Sydney and Melbourne will need to be prepared to deal with the crippling level of heat as global temperatures continue to rise by the end of the century.

Climate scientist Dr Sophie Lewis said the study assessed the potential magnitude of future extreme temperatures in Australia under the conditions outlined in the Paris Climate Accord.

The global agreement which Australia committed to when Tony Abbott was Prime Minister aims to restrict greenhouse gas emissions and limit the increase in global temperatures to between 1.5 and 2 degrees Celsius above pre-industrial levels.

But at the top end of that range, Australian cities could have 50C days as early as 2040 to 2050, Dr Lewis said.

"Over the past couple of years we've had record broken after record broken,” she told news.com.au.

"To be best prepared for future climate change we really need to know what are the extremes of the future, what are these record breaking events going to look like in 10, 20, or 30 years time.”

Co-researcher Andrew King from the University of Melbourne's School of Earth Sciences and the Centre of Excellence for Climate System Science said most climate studies looked at how current temperature extremes had been impacted by climate change, or how the frequency of these current extremes would change.

"This study takes a different approach and examines how the severity of future temperature extremes might change in the future,” Dr King said.

The researchers used data from the Bureau of Meteorology and two sets of climate models - the same ones used by the Intergovernmental Panel on Climate Change to assess how the magnitude of record-breaking events may change in the coming decades.

Dr Lewis said: "We found that we might be expecting those 50C days by 2040.

"But we can delay that if we make drastic cuts to our greenhouse gas emissions that are more ambitious than those outlined in the Paris agreement.”

If not, "one of the hottest years on record globally in 2015 could be an average year by 2025”, she said.

The researchers looked at Sydney and Melbourne due to their large populations and the potential impact extreme heat events could have on the functionality of our large cities.

"If we're having heatwaves that are three to four degrees warmer than now, it's going to be a real challenge to move people across the city. It's going to be a real challenge for our hospitals to cope with the larger number of admissions,” Dr Lewis said.

"Something as simple as sending young children to school on a 50C day is something we have to start talking about and preparing for.”

Potentially contributing to the high temperatures in cities is a phenomenon called the Urban Island Heat effect. According to the Centre for Science Education some cities are regularly up to 5C warmer than surrounding areas.

UCAR says large cities have become hotter as plants and natural vegetation has been replaced by a concrete jungle of buildings and roads.

"These surfaces absorb - rather than reflect - the sun's heat, causing surface temperatures and overall ambient temperatures to rise,” UCAR said.

"Displacing trees and vegetation minimised the natural cooling effects of shading and evaporation of water from soil and leaves. Waste heat from vehicles, factories, and air-conditioners may add warmth to their surroundings, further exacerbating the heat island effect.”

While the researchers did not look at specific locations within an area, the heat-trapping potential of cities is an "additional factor” to consider when it comes to future extreme heat events, Dr Lewis said.

"That is something that has to be a part of the conversation about how we prepare our cities and allowing people to have access to well-ventilated, green areas could really help with coping with extreme temperatures,” she said.

The research, supported by the Centre of Excellence for Climate System Science, was published this week in the journal Geophysical Research Letters.

- Nick Whigham