Climate change is an increasingly important and pervasive pressure on all aspects of the Australian environment. Although our climate and its high natural variability from year to year have always been a major influence on the state of the Australian environment, strong evidence shows that the climate is changing at a rate unprecedented in the geological record. Climate change is altering the structure and function of natural ecosystems, and affecting heritage assets, economic activity and human wellbeing. It also exacerbates the impact of other pressures.
The impacts of climate change are likely to worsen, and some of these impacts may be irreversible. For example, a Queensland Government report released in May 2016 noted the probable extinction of the Bramble Cay melomys (Melomys rubicola)—a species of rodent—from its only known island home in Torres Strait as a result of climate change (Gynther et al. 2016). The key factor responsible for the extinction was the increased frequency and intensity of weather events, which have produced extreme high-water levels and damaging storm surges, and caused dramatic habitat loss and, possibly, direct mortality.
The many consequences of climate change, such as changes to species distributions, restriction of agricultural growing seasons, threats to heritage values and intensification of bushfire conditions, pose the greatest medium-term pressure on Australia’s environment.
Climate change observations and projections for Australia are frequently reported by the Australian Government Bureau of Meteorology, and the Commonwealth Scientific and Industrial Research Organisation (CSIRO; e.g. Whetton et al. 2015). Except where otherwise noted, the following sections have been drawn from these sources.
The average surface air temperature across Australia has increased by 1 °C since 1910, with increasing atmospheric concentrations of greenhouse gases contributing to this rise through the enhanced greenhouse effect. Because heat and carbon dioxide (CO2) from the atmosphere are absorbed by the oceans, the oceans have also warmed, and their chemistry has changed. Sea surface temperatures are continuing to increase nationally, with waters in the South-east Marine Region and the South-west Marine Region increasing the most at more than 0.4 °C per decade from 1982 to 2015. As CO2 dissolves in sea water, it forms a weak acid, resulting in a gradual decrease in the alkalinity of sea water and in the amount of disolved carbonate ion in the water-—a process known as ocean acidification..
Since 2001, the number of extreme heat records in Australia has outnumbered extreme cool records by a factor of almost 3 to 1 for daytime maximum temperatures and almost 5 to 1 for night-time minimum temperatures. The frequency of record high sea surface temperatures across Australian waters has also increased.
In recent years, heatwaves, floods and storms have occurred more frequently in many cities. Since 2001, heatwaves have increased in duration, frequency and intensity in many parts of the country. Major heatwaves are Australia’s deadliest natural hazard, particularly for cities. They have caused more deaths since 1890 than bushfires, cyclones, earthquakes, floods and severe storms combined (DITMCU 2013).
It is not only Australia that has experienced increases in temperature, but also, on average, large areas of the globe. The regions showing the largest change are in the Arctic and Antarctic. In the Antarctic Peninsula region, some areas are showing the largest temperature rises anywhere on Earth (approximately 2 °C since the late 1950s).
Since the 1970s, rainfall has increased in northern Australia, mainly because of an increase in wet-season rain, and declined during the cooler months in the south-east and south-west of the continent.
The weekly frequency of bushfires in Australia increased by 40 per cent from 2007 to 2013 (Dutta et al. 2016). Some care needs to be taken when interpreting an increase associated with such a short time period, but this increase in frequency is likely to be deleterious to some, even fire-dependent, ecological communities (Murphy et al. 2010). Recognition of the cost of bushfires in terms of ecosystem function and environmental services, not just human life and property, has increased (Stephenson et al. 2013).