Figure 1: Examples of extreme weather records broken during Australian summer 2012-13. (Source: Climate Commission)
Australia is recovering from its hottest summer on record, dubbed the “Angry Summer” by the Australian government’s independent Climate Commission.
Australia has been experiencing record heat since September 2012. Central Australia suffered a spate of heatwaves during spring, culminating in late November 2012 with inland temperatures more than 10°C above average. This last heatwave then moved southeast, causing on 29 November Victoria’s highest spring temperature on record (45.8°C in Ouyen), warmth in NSW rivaled only by the February 2009 heatwave (46.2°C in Pooncarie), and extreme heat in South Australia (46.0°C in Marree, with a record-breaking overnight minimum of 32.3°C in Oodnadatta). That was followed by record high overnight temperatures in Tasmania (22.1°C in Hobart) and record humidity in Victoria.
The peak of the summer was a heatwave in January 2013 that was unprecedented in degree, extent, and longevity. It began in Western Australia: in the last week of December 2012, Perth equaled its record of 7 days in a row over 37°C. As the heatwave spread, temperature records were broken across Australia. Every capital city except Brisbane and Darwin reached 40°C at least once. On 4 January, the hottest day in the southeast, Hobart suffered a record-breaking 41.8°C, also the second highest temperature ever recorded in Tasmania. Australia as a whole experienced a record hot temperature of 40.3°C on 7 January, the sixth of seven consecutive days over 39°C (compared to the previous record of four consecutive days).
Catastrophic fire warnings were issued in most of populated southeastern Australia. Fires indeed occurred in every state and territory. On 4 January up to 40 bushfires occurred in Tasmania, burning 25,000 hectares, and up to 140 in NSW on 8 January.
Figure 2: Tasmania on 7 January 2013. Red areas indicate fires. (Source: NASA)
After 8 January the eastern states cooled temporarily, but a second wave of heat swept across the continent, beginning in Western Australia which experienced its hottest temperature on record (49.0°C at Leonora on 9 January). When adjusted for the cooling effect of elevation, the highest temperature ever recorded in Australia occurred at Wiluna, Western Australia on 8 January (48.0°C at 521 metres above sea level). As the heat moved east, parts of South Australia, NSW, and Queensland suffered temperatures above 48°C, including 49.0°C in Birdsville, Queensland’s hottest January temperature. 12 January saw the hottest temperature of the summer: 49.6°C in Moomba, South Australia, the eighth hottest temperature ever recorded in Australia. On 14 January Queensland experienced its highest overnight minimum since 2006 (34.1°C in Bedourie). In a final wave of extreme heat in the southeast, Sydney experienced a record-breaking 45.8°C on 18 January. The heatwave finally ended on 19 January, the first day since 31 December on which no part of Australia reached 45°C.
Figure 3: Map of highest maximum temperatures observed in each part of Australia during 1-14 January 2013. (Source: The Conversation)
During the January heatwave, over 70% of Australia experienced extreme heat. The worst and longest-lasting heat was in central Australia, where maximum temperatures were more than 6°C above average. Birdsville had a record 31 consecutive days over 40°C, and Oodnadatta had a record 7 consecutive days over 45°C. For 5 consecutive days temperatures exceeded 48°C somewhere in South Australia. 44 weather stations set new all-time maximum temperature records (and another 15 set January records), and 7 recorded their all-time warmest night (plus 13 January records). Some stations broke records multiple times during the heatwave. Overall, January 2013 was Australia’s hottest month since records began in 1910.
The extreme heat continued in February 2013. February was unusually hot in northern and western Australia. Parts of Victoria had 20 or more consecutive days above 30°C.
Sea surface temperatures surrounding Australia were the second warmest on record in January and February. Tropical Cyclone Oswald brought extreme rainfall to the east coast in late January, breaking all-time daily rainfall records at 11 locations. Parts of southern Queensland received 700 mm in 24 hours. The Burnett catchment in Queensland and the Clarence catchment in NSW reached record flood peaks, with the former breaking its daily rainfall record by 70%. The Brisbane catchments saw a similar rainfall event to the 2011 floods, except fortunately this time the soil was dry enough to absorb it. This was followed by further intense rainfall and flooding in northern NSW in late February. However, most of Australia had a relatively dry summer: Victoria and South Australia saw their driest summers since the 1980s, and many weather stations experienced record low rainfall.
The summer continued into March 2013. Southeast Australia suffered a long heatwave from 1 to 13 March. Maximum temperatures during the first 12 days of the month were almost 7°C above average in Tasmania and Victoria, and up to 10°C above average around Mount Gambier. Mount Gambier had a record-breaking 11 consecutive days above 30°C. Melbourne had 9 consecutive days above 32°C, its longest spell above 30°C in any month since records began in 1855. Adelaide had 10 consecutive days above 32°C, rivaled only by the March 2008 heatwave. Even if the rest of the month has normal weather, it will easily break the record for Tasmania’s hottest March. Most of southeast Australia also suffered minimum temperatures 5-6°C above average. Melbourne had 7 consecutive nights with minimum temperatures above 20°C, also the longest in any month. On the morning of 13 March, Melbourne had its highest minimum temperature on record, 26.5°C. The extreme heat was combined with high relative humidity and low wind speeds which made it feel even hotter.
Australia’s summer as a whole was the hottest on record, 1.1°C above the 1961-1990 average and 0.1°C above the previous record set in 1997-98. This summer is particularly notable in that it has occurred despite neutral Southern Oscillation conditions, unlike 1997-98 and other previous hot summers which occurred during El Niño events. 97% of Australia was warmer than average, an extent that is unprecedented. Climatologists estimate the chance that natural variation caused all these records is one in 500.
The Climate Commission report says “Australia’s angry summer shows that climate change is already adversely affecting Australians.” This is because all the extreme weather that happens today is occurring in the context of a climate system warmer than it was 50 years ago. An increase in average temperature causes a dramatic increase in extreme hot weather:
Figure 4: Illustration of how increasing average temperature increases extreme high temperatures. (Source: Climate Commission)
If an athlete takes steroids, for example, their base line shifts. They’ll do fewer slow times and many more record-breaking fast times. The same thing is happening with our climate system. As it warms up, we’re getting fewer cold days and cold events and many more record hot events.
Australia has warmed by 0.9°C since 1910. Six of the ten hottest Australian summers have occurred this century. Record hot extremes in Australia in the last decade outnumber record cold extremes by three to one.
Figure 5: Australian summers since 1910. (Image source: The Conversation)
As well as making heatwaves worse, climate change is exacerbating fire risk. Fire risk conditions have also been increasing since 1973; the scale had to be extended upward after the Black Saturday fires of February 2009.
Climate change is also increasing intense precipitation, because there is more water vapor in the atmosphere now than there was 25 years ago:
Figure 6: Illustration of how global warming has changed the water cycle. (Source: Climate Commission)
Southern hemisphere land areas together had their 2nd hottest summer in 2012-13. Many parts of the world have had extreme hot summers in recent years. Almost everywhere in the world there is a trend towards more frequent extreme heat.
Figure 7: Temperature anomalies by percentile around the world. (Source: US National Climatic Data Center)
The events that are occurring now are in the context of just 0.8°C of global warming. The consequences of the ~7°C by 2100 that would result from continuing of business-as-usual would be unimaginably catastrophic. Under a mid-to-high emissions scenario, this summer would become the average Australian summer by 2050.
The Climate Commission concludes:
In Australia and around the world we need to urgently invest in clean energy sources and take other measures to reduce emissions of greenhouse gases. This is the critical decade to get on with the job.