3 Atmosphere | 2 Climate | 2.5 Risks to Australia's climate

State of the Environment 2011 Committee. Australia state of the environment 2011.
Independent report to the Australian Government Minister for Sustainability, Environment, Water, Population and Communities.
Canberra: DSEWPaC, 2011.

3 Atmosphere

2.5 Risks to Australia’s climate

At a glance

For Australia, as the driest inhabitable continent and with a climate characterised by high levels of variability, climate change poses a clear and present threat. At national and regional scales, although there is inevitable uncertainty associated with projections of future climate, the most recent comprehensive review of modelling outcomes shows that a continuing, spatially variable rise in temperatures across the continent is highly likely. By 2030, annual average warming (above 1990 levels) is estimated to be approximately 1.0 °C, varying from an increase of 0.7–0.9 °C in coastal areas to 1–1.2 °C inland. Projections of rainfall are more variable, but half of the 23 models considered by the Commonwealth Scientific and Industrial Research Organisation and the Bureau of Meteorology show an increase in annual and summer rainfall in northern Australia, while nearly all show a decrease in winter rainfall in the south-west and along the south coast. Warmer and drier conditions over much of southern Australia are likely to lead to reduced soil moisture. Intense rainfall events are likely to become more extreme in response to a warmer, wetter atmosphere. Extreme events, such as floods, droughts, heatwaves and fires, are likely to increase in frequency and/or severity. However, although the number of intense cyclones may increase, the total number of cyclones is likely to decline. Such primary ‘atmospheric’ risks generate a broad series of secondary and tertiary risks, many of which are explored elsewhere in this report.

Observations and research outcomes since 2008 have confirmed and strengthened the position that the mainstream science then held with a high level of certainty, that the Earth is warming and that human emissions of greenhouse gases are the primary cause. Garnaut85

As noted in Chapter 2: Drivers, global GHG emissions have (since 2005) continued to track above the middle of the IPCC’s scenario range—between A1B (economic growth based on a balance between resource-efficient and fossil fuel–intensive industries) and A1FI (fossil fuel–intensive growth).86-87 Given the longevity of most GHGs in the atmosphere and the slow rate at which the temperature of the oceans changes, we know that the lower atmosphere and oceans will continue to warm for centuries after emissions are stabilised.88 Even if the most optimistic scenarios for carbon dioxide reductions were to be realised, increased temperatures associated with carbon dioxide emissions will be ‘largely irreversible for 1000 years after emissions stop’.75

In addition to the risks of increasing temperatures and changes in rainfall amount and seasonality, a key risk associated with climate change is the likelihood of more frequent and/or severe extreme weather events, such as floods, droughts and heatwaves, and an increase in bushfires. However, although the number of intense cyclones may increase, the total number of cyclones is likely to decline.50 Such primary ‘atmospheric’ risks generate a broad series of secondary and tertiary risks, many of which are explored elsewhere in this report. These include increased mortality and morbidity due to heatwaves and spread of disease vectors, reduced streamflows and groundwater recharge, reduced soil moisture, and changes in habitat with attendant risk to biodiversity. The summary of risks below assumes a timeframe of 30–40 years.

Assessment summary 3.3—current and emerging risks to Australia’s climate
  Catastrophic Major Moderate Minor Insignificant
Almost certain  
  • Continuing spatially variable rise in temperatures across the continent
    Not considered
Likely  
  • Reduced rainfall in southern areas, especially in winter, and in southern and eastern areas in spring
  • Increased evaporation and reduced soil moisture
  • Increased frequency and severity of wildfires
  • Increased frequency of heatwaves
  • Increased geographic range of disease vectors (e.g. mosquitoes)
  Not considered
Possible
  • One or more climate change tripping points are passed, triggering abrupt, nonlinear and irreversible changes in the climate system
  • Increased severity of extreme weather events such as cyclones
    Not considered
Unlikely       Not considered
Rare Not considered Not considered Not considered Not considered Not considered
 Not considered

Explanation of terms:
Almost certain: >90% probability of occurring during the specified timeframe
Likely: >66% – ≤90% probability of occurring during the specified timeframe
Possible: >33% – ≤66% probability of occurring during the specified timeframe
Unlikely: >10% – ≤33% probability of occurring during the specified timeframe