Australia has started 2013 with a record-breaking heat wave that has lasted more than two weeks across many parts of the country. Temperatures have regularly gone above 48°C, with the highest recorded maximum of 49.6°C at Moomba in South Australia. The extreme conditions have been associated with a delayed onset of the Australian monsoon, and slow moving weather systems over the continent.
The most significant thing about the recent heat has been its coverage across the continent, and its persistence.
So, does all this have something to do with climate change?
To put it in context, we need to look at the influence of background changes in the climate system.
The planet is warming, and so is Australia
Planet Earth is warming up. Climate scientists use a range of different indicators to track global warming. These include ocean heat content, sea surface temperatures, sea level, temperatures in the lower and middle troposphere, and the rate of melting glaciers and ice sheets.
The surface of the earth, as measured by global mean temperature, has warmed by about one degree Celsius during the past hundred years, and the decade from 2001 to 2010 has been the warmest we have recorded.
This warming has been strongly attributed to increasing greenhouse gases from human activities. While there are a number of influences on the climate system, such as changing solar radiation and changing atmospheric aerosols, it is very clear that warming has been dominated by increased carbon dioxide levels.
The globe doesn’t warm uniformly everywhere, due mostly to natural regional variations in climate. In Australia, land temperatures and the temperatures of the surrounding oceans have warmed by approximately 1°C since 1910, fairly close to the global trends.
A warmer planet means a warmer atmosphere for all our weather and climate
As the climate system warms due to increasing greenhouse gases, more energy is retained in the lower atmosphere. That extra energy influences all our weather and climate.
We’re seeing more record-breaking heat events than cold events
A relatively small change in the average temperature can easily double the frequency of extreme heat events. Australia has warmed steadily since the 1940s, and the probability of extreme heat has now increased almost five-fold compared with 50 years ago.
Within the past decade, the number of extreme heat records in Australia has outnumbered extreme cold records by almost 3:1 for daytime maximum temperatures and 5:1 for night-time minimum temperature.
The duration of heat waves has increased in some parts, especially in the northern half of the continent. Put another way, the frequency of abnormally hot days (above the 90th percentile) has increased by 30% and the frequency of hot nights (above the 90th percentile) has increased by 50%.
It is worth noting the summer just gone in the US was the warmest on record, with extreme heat records broken at a rate never previously seen before. Studies here and overseas are now showing that many of the recent extreme summer heat events around the world — such as the European heat wave of 2003, the Russian heat wave of 2010, and US heat waves during 2011 and 2012 — would have been very, very unlikely without the influence of global warming.
Global warming is not only warming summer but also broadening the summer-like period of the year, creating the perfect set-up for record extreme heat.
Of great concern in Australia is the substantial increasing trend in severe fire weather — weather conducive to the spread and intensification of bushfires and grass fires — in about half of the monitoring sites studied around the country, with a concentrated increase in the southeast of the continent. The fire season is now longer, reducing the time for preparation such as fuel reduction.
Again this is not surprising, and has been predicted in advance — the combined impact of warming and cool season drying is increasing the fire danger in a region already highly fire prone.
We expect extreme warm weather events will occur more often
Future warming of the climate due to greenhouse gas emissions will very likely lead to further increases in the frequency of unusually hot days and nights and continued declines in unusually cold days and nights.
And it’s not just temperature extremes. Climate model projections indicate that the frequency of many different types of extreme weather will change as the planet warms.
As you might recall from our previous post: The most compelling investment themes for 2013 – Australia is major exporter of many resources imported by China – expect lots of volatility and investment opportunities.
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