Climate change in Australia - the unpleasant reality

By Trisha Cashmere.

Key Points:
Changes projected for the period 2050-2070 may vary depending on the emissions trajectory from now and going forward.

The CSIRO has released a report, "Climate Change in Australia - technical report 2007" which provides an assessment of the observed climate change over Australia, considers the likely causes, and provides projections of future climate changes. The report is based on international climate change research and includes research completed within the Australian Climate Change Science Program by the CSIRO and the Australian Bureau of Meteorology. The report includes conclusions from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

Although climate change knowledge has improved markedly over the past several decades and continues to improve, the issue is still clouded by uncertainty. The sources of uncertainty are many and diverse but can be grouped into:

• socio-economic uncertainties associated with the current and future activities of humans
• scientific uncertainties associated with our understanding of how the Earth’s major biophysical systems behave; and
• fundamental uncertainties associated with the behaviour of complex systems.

The report sets out what the CSIRO considers to be the hard facts, and is intended to provide sufficient information for businesses and individuals to assess and manage their exposure to climate change risk.

Past climate change

The CSIRO report concludes that since 1950:

• average temperatures in Australia have increased by 0.9°C
• the frequency of hot nights also has increased
• Southern Ocean temperatures have increased to a depth of 1000m
• sea levels have risen at all Australian monitored sites; and
• rainfall trends have demonstrated a increase in the relatively unpopulated north-west regions with contrasting drying along the east coast exceeding 50mm per decade.

In addition to those changes, the CSIRO notes that recent droughts are the hottest on record and with higher minimums and maximums recorded than in previous drought periods.

There has also been a 17 cm increase in global sea levels during the 20th century. The observed rate of increase since 1993 has been 3 mm per year. There has been substantial warming of the oceans surrounding Australia to a depth of up to 1000 m, and this is associated with a southward migration of the Antarctic Circumpolar Current[1]. There has also been a reduction in the salinity near the bottom of the ocean near Antarctica.

Causes of past climate change

Climate change can be a result of both natural and anthropogenic factors. However the CSIRO considers that the significant increases in Australian surface temperature since the 1950s are most likely to be due to anthropogenic causes.

The post 1950 rainfall decreases in eastern Australia and rainfall increases in north-Western Australia cannot yet be attributed to human activities, unlike the decrease in rainfall since the mid 1970s which is stated to be at least partly due to anthropogenic increases in greenhouse gases. Recent droughts have been accompanied by higher surface temperatures. It is stated that the higher temperatures which have exacerbated the impact of the droughts due to increases in water demand and surface water loss have been due to anthropogenic warming.

The report also concludes that the increasing number of warm days and nights and decreasing number of cool days and nights is likely due to human activity.

Climate projections

The report provides global and regional climate change projections through to 2070, which will assist businesses in their risk management analysis and planning.

Near term projections of changes in climate vary little with different emissions scenarios because the majority of these changes will be the result of emissions that are already in the atmosphere. It is those changes projected for the period 2050-2070 that may vary depending on the emissions trajectory from now and going forward.

At 2030 the best estimate is a temperature increase of 1ºC relative to 1990, with slightly lower increases in coastal regions and higher increases inland. For the period 2050 to 2070 the variability in the forecasts becomes greater as the projections are dependent upon the future emissions trajectory. In 2050 with a low emissions trajectory it is anticipated that the average warming around Australia will be around 1.2ºC, while a high emissions trajectory would see average temperatures increase by around 2.2ºC. By 2070, the increase in the low emissions trajectory is around 1.8ºC, with the high emissions trajectory seeing average temperature increases of 3.4ºC (range 2.2 to 5ºC).

The regional variations follow those seen in the 2030 projections, with the south and north-east experiencing less warming, and inland areas experiencing more.

Rainfall projections for 2030 suggest reductions of 2% to 5% in majority of the country, with little change in the far north. Seasonal variations are greater, where decreases of around 10% are expected in the south west. There is significant variation in the various models to 2050, however the best estimate is decrease of 5% in southern areas using the low emissions scenario. High emissions projections are for decreases of 7.5% through the southern parts of the country. Again there are seasonal variations, with the decrease of rain in winter of up to 30%.

In 2070 the low emissions projections mirror those of the low emissions 2050 scenario. The high emissions projections are for rainfall decreases of around 10% with seasonal variations on the south-west of up to 40%. However, though there won't be many wet days, when they do occur the intensity of rain will increase.

Extreme weather

The CSIRO opines that:

• future weather will be characterised by increasing drought, decreased humidity, increased wind speed, especially in coastal areas and a substantial increase in fire weather risk in south-eastern areas;
• global sea level rise in projected to be 18-59 cm by 2100. This could increase by a further 10 to 20 cm for ice sheet melting. These conditions will exacerbate the impact of storm surges which will inundate further inland causing increasing damage to the natural and built environments; and
• the intensity of cyclones is expected to increase, though there may be some reductions in frequency. There may be some increase in hail risk.

Implications

At present the focus of much of the business community appears to be emissions reductions. This is important and the outcomes achieved will have impacts on the climate outlook from 2050 going forward. However, changes to our climate are happening, and will continue. The CSIRO's recent report demonstrates that managing climate change risk does not just mean factoring a price of carbon into the balance sheet, but also managing the risk that will come with the consequential changes to the climate and environment.

 

[1] The Antarctic Circumpolar Current is the most important current in the Southern Ocean, and the only current that flows completely around the globe, according to Ryan Smith, Melicie Desflots, Sean White, Arthur J. Mariano, Edward H. Ryan. "The Antarctic CP Current." Ocean Surface Currents (accessed 23 November 2007).

 

For further information, please contact Brendan Bateman.