New papers examine Australia's weird weather

The annual extremes issue of the Bulletin of the American Meteorological Society features five papers focusing on Australia’s changing climate throughout 2014.

The papers — three from the ARC Centre of Excellence for Climate System Science (ARCCSS), one from CSIRO and one from the Bureau of Meteorology — look at the role played by climate change on the two hot days felt during the G20 World Leaders Forum; the January heatwaves in Melbourne and Adelaide; a 19-day heatwave in May; the hottest spring on record; and an unusual stalled weather pattern that contributed to severe frost across south-east Australia.

“In nearly every case we investigated, global warming was found to have had a clear impact on Australia’s extreme events,” said ARCCSS Chief Investigator Professor David Karoly, a co-author on three of the papers.

“Climate scientists have long expected an increase in extreme heat events to be the first apparent symptom of global warming. The pronounced increase in these events shows how global warming has started to change our world.”

Dr Sarah Perkins-Kirkpatrick’s paper focused on the 19-day Australia-wide heatwave in May 2014. The results suggest heatwaves like these are now almost 20 times more likely as a result of human-caused carbon emissions.

“Looking into the near future, the likelihood of a similar heatwave during May continues to climb, becoming almost 24 times more likely by 2020,” Dr Perkins-Kirkpatrick said.

Research led by Dr Andrew King meanwhile suggests that global warming may have made an appearance during the G20 Leaders Summit. He found that as a result of global warming, the 34°C temperature of the first day of the Brisbane summit was 25% more likely and 38°C November days are now 44% more likely.

Meanwhile, Mitchell Black’s investigations into the January heatwave that struck the Australian Open and Adelaide were less clear. While climate change probably increased the odds of the four days above 41°C that plagued Melbourne Park, there was a small chance that it was due to natural variability. By contrast, climate change increased the odds of the Adelaide heatwave, which had five consecutive days above 42°C, by at least 16%.

Climate change can also affect conditions linked to frosts, as a team led by CSIRO’s Dr Michael Grose discovered when they examined an unusual high surface pressure anomaly formed off the south coast of Australia in August 2014. From that position, it actually drove clear skies that contributed to severe late-season frosts across south-east Australia and were linked to snow down to 200 m in Tasmania. The researchers found climate change doubled likelihood of such conditions.

Dr Pandora Hope from the Bureau of Meteorology led the study that looked at our hottest spring on record in 2014. Her team found that global warming likely played an important role in that record-setting season, particularly as a result of extremely warm ocean temperatures.

“Together, these five papers looking at extreme events in 2014 show just how much global warming has become a part of today’s climate,” said Professor Karoly.

“We have just experienced Australia’s hottest October on record and, globally, 2015 looks likely to smash the hottest year on record yet again. These expected and obvious signals of climate change confirm as we move towards the Paris Climate Meeting that global warming is already with us.”