It's likely human influence has been the dominant cause of the observed global warming since the mid-20th century, due to increases in greenhouse gases.

Last week, South-eastern Australia roasted under another heatwave. Adelaide had 5 days between 42 and 45°C, Melbourne had 4 days over 41°C (a new record) and Canberra had 5 days over 37°C.

Sequence of temperature maps from the Bureau of Meteorology showing the movement of hot air from western to eastern Australia from 11-17 January 2014.
Sequence of temperature maps from the Bureau of Meteorology showing the movement of hot air from western to eastern Australia from 11-17 January 2014.

The cause was a blocking high pressure system in the Tasman Sea which funnelled hot winds over the region. This air had been cooking for a while – it was hotter than 39°C when it moved from WA into northern SA on 10 January, then into western NSW on 11 January, southern SA and western Victoria on 13 January, and the rest of Victoria and Canberra on 14 January (Figure 1).

This heatwave followed on from the heat of 2013, which was Australia’s warmest year on record since measurements began in 1910 (Figure 2). Over the past decade, the number of extreme daytime heat records in Australia outnumbered extreme cold records by almost 3 to 1. These increasing temperatures are part of a global warming trend.

According to the Intergovernmental Panel on Climate Change (IPCC), it is extremely likely that human influence has been the dominant cause of the observed global warming since the mid-20th century, due to increases in greenhouse gases. An increasing number of studies have partly attributed the rise in extreme heat events to this increase in greenhouse gases.

Next time it will be worse

In the future, heatwaves are very likely to be longer and occur more often, according to the IPCC.

Annual Mean Temperature Anomalies for Australia 1910-2010. BoM.
Annual Mean Temperature Anomalies for Australia 1910-2010. BoM.

CSIRO and the Bureau of Meteorology have estimated that the annual average number of days over 35°C may increase from 9 days at present in Melbourne to 12-26 days by 2070 (Table 1).

Adelaide will go from 17 days over 35°C to 24-47 days by 2070.

Perth will go from 28 days over 35°C to 36-76 by 2070 and Canberra will go from 5 days to 8-26 days by 2070.



Current average days per year over 35°C Medium emissions (2030) Low emissions (2070) High emissions (2070)
Perth 28 36-43 36-46 48-76
Alice Springs 90 102-118 112-138 132-182
Sydney 3.5 4.1-5.1 4.5-6.6 6-12
Melbourne 9 11-13 12-17 15-26
Brisbane 1 1.5-2.5 2.1-4.6 4.0-20.6
Canberra 5 7-10 8-14 12-26
Adelaide 17 21-26 24-31 29-47
Hobart 1.4 1.6-1.8 1.7-2.0 2.0-3.4
Table 1. Current and projected annual-average number of days over 35°C at selected Australian cities. The current period is defined as 1971-2000. Projections are for 30-year periods centred on 2030 and 2070, for low (B1), medium (A1B) and high (A1FI) IPCC greenhouse gas and aerosol emissions scenarios. Projections for medium emissions in 2030 are very similar to those for low and high emissions.

Heatwaves cost us

Heatwaves have significant impacts for health, infrastructure, ecosystems and agriculture, and these are likely to grow in the future.

For example, the heatwave in southeast Australia in late January 2009 caused 374 excess deaths. This heatwave set up conditions for the February 2009 bushfires in Victoria which caused 173 deaths and about $4.4 billion in damage.

Since 1994, more than 30,000 flying foxes died in heatwaves at sites along the east coast of Australia. Over 3,500 flying foxes were killed in January 2002 along the New South Wales coast due to extreme heat. While in January and February 2009, nearly 5,000 flying foxes died at Yarra Bend Park in Melbourne.

Agricultural productivity and profits decline when livestock suffer heat stress. Extreme temperatures also reduce crop yield and quality.

Blackouts and infrastructure breakdown

Heatwaves can lead to black-outs due to increased energy consumption for air conditioning. For example, during the January 2009 Victorian heatwave, electricity demand soared and the Basslink electricity cable between Tasmania and Victoria had to be shut down for safety reasons. Around 500,000 people were without power, breaking all previous records for Victoria. Water consumption also increases during heatwaves.

Extremely hot days can cause transport delays due to fires, buckling train lines and air conditioning faults. On 30 January 2009, approximately one quarter of Melbourne train services did not run due to buckled train lines and equipment faults. Financial losses from heatwaves can run into many millions of dollars.

Protecting ourselves

In the short term, we need improved early warning systems and better preparation of communities, emergency services, health and medical services, transport and energy services. We also need to educate the community on how they can reduce their exposure to heat stress, including making sure they stay cool and drink lots of water, head to shopping centres to take advantage of the air-conditioning, and never leave children or pets alone in a car.

Benefits of future proofing our cities and farms

In the longer term, we can build more resilient cities by increasing vegetation to reduce urban heat islands, providing incentives for better designed homes that are cooler and more energy-efficient, and improving management of peak demand loading on the electricity grid.

Our cites will need to be built differently using improved engineering design standards, with less heat-sensitive materials and better maintenance routines for essential services.

We also need to implement emergency response plans that encourage adaptability through collaboration across agencies.

In agriculture, we can develop and select more heat-tolerant crops, and provide shade and water for livestock.

These and other actions are included in the National Strategy for Disaster Resilience, and some are already being implemented. Our challenge is to identify and overcome the remaining barriers to prevention, preparedness, response and recovery.