Climate change

2011

Climate has always been a prime determinant of the Australian environment and its condition, with droughts and floods perhaps more characteristic than for other inhabited continents. The recent drought in south-east Australia is unprecedented in both its length and intensity (lasting from 1997 to 2010 in some areas). Research has shown that changes in the large-scale weather patterns affecting south-east Australia are associated in part with climate change. Therefore, it is likely that climate change, together with natural variability—and potentially land-use change6—contributed to this drought. Similarly, research has found that the rainfall decline in south-west Western Australia since the mid-1970s is likely to be at least partly due to anthropogenic (caused by human activity) increases in GHGs.7 The drought in south-west Western Australia continues unabated. Understanding the causes and consequences of such events is crucial to any assessment of the current state of our environment and its recent trends.

There is strong and growing evidence that our climate, with its very high natural variability from year to year, is changing at a rate unprecedented in the geological record. Therefore, any outlook for the environment must incorporate our climate. The implications of climate change are potentially profound, and extend beyond the more obvious and direct impacts on inland waters, terrestrial and marine ecosystems and biodiversity, to our cultural heritage and built environment.

Forward projection of climate is scientifically challenging and inherently uncertain. There is a strong scientific consensus that anthropogenic emissions of GHGs have an impact on climate. New climate science and climate modelling is regularly published. The most robust statements on climate change since the 2006 State of the Environment report8 reside in the Intergovernmental Panel on Climate Change’s (IPCC) fourth assessment report.9 The significance of this body of work lies not only in the breadth and scope of the science contributing to the assessment, but also in the structured comparison of climate projections based on 23 of the world’s global climate models across an agreed set of emissions scenarios.10 The results of this comparison give us a picture of the strong commonalities among the global climate model predictions, as well as the uncertainties in their predictions of climate and GHG emissions. The IPCC’s scientific undertaking to produce and review the material for the fourth assessment report is impressive and unique. In the time since its release, aspects of the reporting process have been challenged, but not the underlying scientific content.

Has the science of climate change, as reported in the fourth assessment report—and now nearly four years old—significantly departed from those findings in that time? In response to the widespread interest in this general question, climate change science and data were reviewed and updated in time for the 2009 Copenhagen Climate Summit.11 The report reinforced the basic scientific linkages between human activity and climate reported by the IPCC, and found that global carbon dioxide emissions from burning fossil fuel continue to track near the highest scenarios considered by the IPCC. The Climate Commission’s 2011 report, The critical decade: climate science, risks and responses, makes the reality, certainty and implications of our changing climate clear and immediate.12

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the Bureau of Meteorology (BoM) summarised the IPCC findings with respect to Australia.13 Climate projections are available for the nation, and every state and territory, for the years 2030, 2050 and 2070. These projections include seasonal and annual rainfall and temperature estimates relative to the period 1980–99. Uncertainty in these projections for a given emissions scenario reflects the degree of disagreement among the global climate models, uncertainty in the scenarios and underlying uncertainty in our ability to capture natural processes in our climate models.

Emissions-driven climate change is obviously dependent on the anticipated use of fossil fuels into the future. The IPCC special report on emissions scenarios10 groups emissions scenarios into four families (A1, A2, B1 and B2). Each of these represent alternative development pathways and resulting GHG emissions under current policies, but with varying rates of population increase, economic growth and increases in resource-use efficiencies. The low, medium and high scenarios referred to in the CSIRO and BoM projections13 correspond to the B1 (economic growth based on clean, resource-efficient technologies), A1B (economic growth based on a balance between resource-efficient and fossil fuel–intensive industries) and A1FI (fossil fuel–intensive growth), respectively. The projected emissions from the IPCC special report are shown in Figure 2.2. Since 2005, global GHG emissions have continued to track above the middle of the IPCC’s scenario range—between A1B and A1FI, with the temporary consequences of the 2008–09 global financial crisis evident.

The estimated increase in annual average temperature by 2030 (relative to 1990) is around 1.0 °C, with warming of 0.7–0.9 °C in coastal areas and 1–1.2 °C inland. By 2050, projected annual warming ranges from 0.8 °C to 1.8 °C; by 2070, the projected warming ranges from 1.8 °C (low GHG emissions scenario) to 5 °C (high emissions scenario). Figure 2.3a illustrates the low and high probability estimates for warming in 2030. There are indications from climate modelling that temperature extremes may also be changing, with a strong projected increase in warm nights, fewer frosts and longer heatwaves.15

The IPCC climate model results indicate that rainfall is likely to be reduced in southern areas of Australia, especially in winter, and in southern and eastern areas in spring. The contraction in the rainfall belt towards the higher latitudes (Figure 2.3b) would likely cause these variations. Future changes in summer tropical rainfall in northern Australia remain highly uncertain. Nevertheless, it is likely that the most intense rainfall events in most locations will become more extreme and more frequent, driven by a warmer, wetter atmosphere.

(2011). Drivers: Climate change. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/2-drivers/2-climate-change, DOI 10.4226/94/58b659517ce65