The CSIRO and Bureau of Meteorology State of the climate 2014 (CSIRO & BoM 2014) concluded that, in the coming decades, Australia’s temperatures are projected to continue to rise. This rise will manifest as an increase in the number of hot days and warm nights, and a reduction in the number of cool days and cold nights. By 2030, projections show average temperatures rising by 0.6–1.5 °C (compared with the climate of 1980–99), in addition to an existing rise of around 0.6 °C between 1910 and 1990. By 2070, if growth in GHG emissions continues in line with past trends, projected warming will be in the range of 2.2–5.0 °C. For low GHG emissions scenarios (which assume a significant reduction in global emissions in the coming decades), the projected increase is 1.0–2.5 °C.
Changes in average rainfall across Australia will also occur. By 2070, average rainfall across southern Australia is projected to decrease compared with the climate of 1980–99: between 0 and 20 per cent decrease under low GHG emissions scenarios, and between 30 per cent decrease and 5 per cent increase under high emissions scenarios. The largest decreases will occur in winter and spring. For northern Australia, the projected changes in rainfall range from a 20 per cent decrease to a 10 per cent increase by 2070 for low emissions scenarios, and a 30 per cent decrease to a 20 per cent increase for high emissions scenarios (CSIRO & BoM 2014).
Anthropogenic climate change may also alter the frequency and severity of extreme events, such as storms (tropical cyclones, storm surges, severe winds and hail), floods, droughts, heatwaves and fires. The IPCC has summarised the projections of climate change and some extreme events for Australia (see Reisinger et al. 2014; Figure ATM17):
- Tropical cyclones are projected (with low confidence) to decrease in occurrence, but their intensity is projected to increase. One modelling study showed (with low confidence) a 50 per cent reduction in tropical cyclone occurrence for 2051–90 relative to 1971–2000, increases in intensity of the modelled storms, and occurrence around 100 kilometres further south (Abbs 2012). Limited studies have shown a projected decrease in the frequency of cool-season tornadoes (Timbal et al. 2010), and increases in the frequency and intensity of hail in the Sydney region (Leslie et al. 2008).
- Extreme precipitation events are projected (with medium confidence) to increase in intensity. Flood risk in the north of Australia (driven by convective rainfall systems) will be greater than in the south of Australia, where more intense extreme rainfall will be offset by drier precursor moisture conditions (Alexander & Arblaster 2009, Rafter & Abbs 2009).
- Sea level rise is projected (with a high level of confidence), which will result in an increase in the frequency of extreme sea level events. Changes in storm surges will play a lesser role (McInnes et al. 2013).
- Droughts are projected (with a medium level of confidence) to become more frequent and severe in southern Australia, with projected changes being more pronounced during winter and spring (Irving et al. 2012).
- Heatwaves are likely to become more frequent, with hot days and nights projected with high confidence to become more frequent (CSIRO & BoM 2014).
- The number of days with very high and extreme fire weather is expected to increase, more so in southern Australia, where fire is weather constrained, than in the tropical savannas of northern Australia, where fire is constrained by fuel load and ignitions. The length of the fire season will also increase in many already high-risk areas, thus reducing opportunities for controlled burning (Lucas et al. 2007). In addition, higher CO2 levels may increase vegetation growth, thus increasing fuel loads in some regions (Bradstock 2010, Hovenden & Williams 2010, King et al. 2011).
A number of these changes may be attributable to a mixture of climate change and natural processes. In any case, improving our understanding of the vulnerabilities associated with such changes is an essential step in planning our adaptation to climate change.