Australasian Science: Australia's authority on science since 1938

Record Summer a Sign of Things to Come

By Stephen Luntz

The record-breaking heat waves of last summer and autumn were not isolated incidents. Dr Sarah Perkins of the Centre of Excellence for Climate System Science at the University of NSW has revealed a trend towards periods of unseasonably warm weather.

Definitions of heat waves vary by city so Perkins defined a heat wave as at least 3 days falling into the hottest 10% recorded at the relevant location and time of year. This enabled her to look not only at the summer months but exceptional periods year-round.

“Interestingly, the anomalous warming events during the cooler months revealed through our research were increasing faster than summer heat wave events,” she says.

Warmer winters have appeal, but Perkins notes that many fruits need cold conditions in winter to reproduce and may be threatened by these conditions.

The pattern has not been even across the country. In some areas heat waves have become more frequent, but in Victoria and South Australia the number is unchanged while the average length has expanded.

Australian temperatures have risen faster than the global average, which Perkins says is probably because continents heat up faster than oceans. However, she is unsure why the number and extremity of peak events seems to be growing faster than the mean temperature.

“We need to be aware that a lot of the impacts of climate change come from the extreme events, so we need to concentrate on these as well as the mean,” Perkins says. She is also unsure why the winter records are falling faster than those in summer.

While publication of the research in the Journal of Climate made a splash after south-eastern Australia’s extraordinary summer, Perkins’ data stretched from 1951 to 2008, missing not only this year’s records but those that triggered the 2009 bushfires.