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Author: T. Arup
Source: The Age
Date: 6th November 2015

Scientists have linked climate change to several extreme weather events that hit Australia last year, including city melting heatwaves, record hot spring temperatures and the sweltering conditions that greeted the G20 meeting in Brisbane.

They are part of a series of new studies – published in a special edition of the Bulletin of the American Meteorological Society – examining the emerging scientific area of extreme weather “attribution”

Dr Andrew King, from the Centre of Excellence for Climate System Science, said attribution was a new area of science.

“Now we can say the likelihood of the hot days in Brisbane or Adelaide, or the hot springs across Australia, are being increased significantly and substantially by climate change,” Dr King, the co-author of the study into the Brisbane G20 meeting temperatures, said.

The results are largely drawn from computer modelling techniques comparing current climate conditions to pre-industrial times. They are then expressed as probabilities – a reflection that the climate system is influenced by natural and human factors, and that it is a developing area of scientific examination.

But the journal says recent scientific developments suggest that “event attribution that detects the effects of long-term changes on extreme events is possible”.

Here is a brief summary of the Australian findings.

Adelaide heatwave – 13 to 17 January 2014

The city of churches sweltered for five consecutive days with temperatures above 42 degrees. On January 16, when temperatures hit 44.2 degrees, the World Metrological Organisation declared Adelaide the planet’s hottest city that day.

To beat the heat the city council set up big fans and water mist sprays in Rundle Mall and warned people to dress light and stay out of the heat. There were reports of numerous hospital admissions for heat related health problems.

FINDING: Human caused climate change has increased the likelihood of an Adelaide heatwave like the January 2014 event by at least 16 per cent and by a best estimate of 186 per cent.

Melbourne heatwave – 14 to 17 January 2014

The heatwave that hit Melbourne was similar to the Adelaide event, but not quite as intense. All up there were four consecutive days above 41 degrees.

It resulted in an estimated 167 excess deaths and is considered to have cost city traders $37 million. Players at the Australian Open collapsed and retired from matches.

FINDING: The influence of human caused climate change on Melbourne summer heatwaves, like that in 2014, is less clear than Adelaide. Climate change increased the odds by a best estimate 89 per cent, but with high uncertainty and a 10 per cent chance it was due entirely to natural factors.

19-day heatwave across Australia – 8 to 26 May 2014

Places where temperature records were set during the Autumn 2014 heatwave. Source: Bureau of Meteorology Places where temperature records were set during the Autumn 2014 heatwave. Source: Bureau of Meteorology

For most of May 2014 the average temperature across the country was 2.52 degrees above the long term observations. The event set numerous temperature records across the country including the longest streak of May days above 20 degrees in Melbourne, Sydney and Adelaide.

While heatwaves are normally perceived as summer events, they also occur in cooler seasons. They tend to have little direct impact on humans, but can lead to the drying out of soil and vegetation exacerbating drought and bushfire risk.

FINDING: Human caused climate change has increased the risk of Australian heatwaves during late autumn, like the 2014 event, by up to 23 times.

Exceptional mean sea level pressure – August 2014

When you watch the TV weather news the mean sea level pressure is represented by those curved lines you see spread out over a map of Australia. They represent a central part of the weather system – such as highs and lows – that influence winds, and in turn how hot, cold, or wet it is going to be.

Last year there were intense and record breaking sea level pressure events in the Great Australian Bight and the Tasman Sea. West of Tasmania pressure readings were at their highest on record since 1850. Later in the month record readings were taken in the south Tasman.

The strongest events were associated with severe frosts in southern Australia, snow down to 200 metres in Tasmania and reduced rainfall in some parts of south-east Australia.

FINDING: The high sea level pressure anomaly in August was about twice as likely to occur given human caused climate change.

Record hot spring – September to November 2014

Australian mean temperatures for spring 2014. Areas which were warmest on record shown in dark orange. Source: Bureau of Meteorology

Australian mean temperatures for spring 2014. Areas which were warmest on record shown in dark orange. Source: Bureau of Meteorology

Spring 2014 saw the highest average temperatures for the season since records began in 1910. Average maximum temperatures across the three months were 2.32 degrees above the long term mean and 0.26 degrees above the previous record, set the year before.

While September was warm, October and November were scorching. The latter two months both set records for the average daily maximum temperature. However, the October record lasted for just one year and was broken again in 2015.

The 2014 hot spell also brought forward the date for the earliest seasonal recording of 45 degrees in the country by 12 days. Bidyadanga in the west Kimberley hit 45.2 degrees on October 9.

FINDING: The record warm spring of 2014 would likely not have occurred without the increases in carbon dioxide levels over the last 50 years, working in concert with the pattern of the high and lows that season.

 A hot G20 in Brisbane – 15 and 16 November 2014

As the world’s most powerful leaders met in Brisbane for the two day G20 meeting, the temperatures outside soared well over the long-term average maximum of 27 degrees.

On the first day the city hit 34 degrees. By the second, temperatures were close to 39.

At the same time climate change was a hot topic. Then Australian Prime Minister Tony Abbott controversially left climate change off the meeting’s official agenda, despite many world leaders wanting otherwise.

FINDING: Human caused climate change has very likely increased the odds of hot November days in Brisbane like those during the G20 meeting by 25 per cent (November 15) and 44 per cent (November 16).

These studies were undertaken by researchers at the following institutions: American Meteorological Society; Bureau of Metrology; ARC Centre of Excellence for Climate System Science, National Centre for Atmospheric Research, Boulder, Colorado; University of Melbourne; CSIRO.

Read the article on The Age