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From a natural disaster perspective, Australia is having a much worse year than New Zealand, despite our apparent penchant for earthquakes, volcanic eruptions, flooding, and the occasional crippling winter storm on this side of the ditch. To date, the Insurance Council of Australia has officially declared three natural disasters in 2013 (the Tasmanian bush fires, New South Wales bush fires, and cyclone Oswald). But is Australia’s exceptional season for extreme weather just a blip on an otherwise “normal” climate regime, or is it perhaps a harbinger of worse things to come as our climate continues to warm?

Worse than the Queensland flooding of 2011?

Our poor neighbours across the ditch have been enduring scorching temperatures and raging bush fires for nearly a month, and now the east of the country is being thrashed by extreme weather, this time of the wet variety, courtesy of cyclone Oswald.  Just over a year after Australian Prime Minister Julia Gillard called the Queensland floods (December 2011 version) “the worst natural disaster in our history” , Queensland and northeastern NSW are once again being battered by extremely stormy weather, including widespread flooding and tornadoes.

Four people have been already been killed by flooding and storm-related hazards in Queensland, since cyclone Oswald made landfall. Communities such as Bundaberg in Queensland and Grafton in New South Wales are experiencing the worst flooding on record, while parts of Sydney have seen the heaviest rainfalls in over a decade.

The link between extreme weather and climate change

So do these recent extreme-weather-related natural disasters indicate that Australia’s climate is becoming more extreme in a broader sense? After all, heat waves and bush fires have historically been a regular fixture of the Australian climate; the same can be said for tropical storms which affect the east coast of Australia.

Actually, these types of extreme weather have become more frequent, and more severe in recent decades. A few decades ago in Australia, the number of new record high temperatures each year was approximately balanced by the number of new record low temperatures. Recently, the ratio of new record highs to new record lows has increased to 2:1. In 2010, 19 countries set new all-time record highs, but no new low temperature records were set.

Climate warming doesn’t directly cause natural disasters like heat waves, bush fires and tropical storms, but it can contribute to more extreme weather in several ways, including:

  • A warmer atmosphere can hold more water vapour, increasing the risk of extreme precipitation,
  • Higher temperatures increase the rate of evaporation from soil and water surfaces, as well as evapotranspiration by plants, increasing the frequency and intensity of droughts,
  • Higher sea-surface temperatures can cause changes in oceanic and atmospheric circulation patterns, which are driven by gradients in temperature and salinity,
  • Warming oceans provide more energy for the development of tropical storms,
  • Rising sea level due to melting ice means that many populated areas are increasingly at risk from tsunami and storm surges.

Weather now develops in different climatic conditions than it did just a few decades ago; heat waves are longer and hotter, tropical storms are more frequent and more intense, as are periods of drought.  The cold(?) hard reality is that extreme weather events that can contribute to natural disasters are on the increase.

The graph below illustrates why a small increase in mean annual temperature can shift the climate curve so that extreme heat events become more severe, and much more frequent. Case in point; the extremely hot conditions of this Australian summer are difficult to attribute to a simple blip on an otherwise normal climate regime; far from just a few days of unusually hot weather, much of Australia has been baking for months. A new record was set for average maximum daytime temperatures during the last 4 months of 2012 (which were 1.6 degrees above average ).

Solomon et al. 2007

 

The hottest day ever in Australia: blistering heat and bush fires

Since the new year, fire-fighting crews have battled hundreds of bush fires in south-east Australia, including in New South Wales, Victoria and Tasmania. Prolonged extreme heat combined with high winds to create ideal fire conditions. Average maximum temperatures across the country soared to 40.33 degrees on 7 January, the hottest day ever recorded over the Australian continent; even the Tasmanian capital Hobart reaching nearly 41 degrees. For the first time ever, the continent recorded five consecutive days with an average temperature exceeding 39 degrees; each of the first six days of 2013 were amongst the 20 hottest days on record.

The heat dome over Australia, 7 Jan, 2013 (Image courtesy of Australia’s Bureau of Meteorology)

1.6 degrees above average is a startling increase when averaged over a four month period, but it isn’t just Australia that has been experiencing a warmer climate: according to the Climate Change Research Centre (University of NSW), the number of very warm days (defined by the warmest 5% of days between 1950 and 1980) has increased by nearly 40% globally since 1983.

Whatever the sceptics may say, our climate is becoming more extreme, and Australia is merely the latest place to suffer from the effects of global warming.