Chapter 4 Climate Impacts and Responses

Impacts of Climate Change on Australia > Natural Systems

There is a complex inter-relationship between climate and environment, with changes in each impacting on the other, often interactively. The second comprehensive and independent national assessment of Australia’s environment, the Australian State of the Environment Report 2001, concluded that while environmental protection has progressed significantly, there are still threats to natural systems. In 2001, the Commonwealth Government declared land clearance as a key threatening process to the environment and biodiversity, observing that the rate of land clearance has accelerated with as much land cleared in the last 50 years as in the 150 years prior to 1945. Only four other countries exceeded the estimated rate of clearance of native vegetation in Australia in 1999. Greenhouse gas emissions associated with changes in land use have been a key contributor to global warming, albeit at a lower level than fossil fuel emissions.

The wetlands of Australia are already under threat from dams, irrigation, coastal urban development, and pollution of waterways. The Murray-Darling Basin Commission has reported that the quality of wetlands has been significantly reduced in the Murray-Darling Basin, particularly between the Hume Dam and Mildura. Climate change and sea level rise would add to the vulnerability of wetlands. If sea levels rise significantly, the vast freshwater floodplains of northern Australia will be subject to significant saltwater inundation (CSIRO, 2002).

Researchers at the Cooperative Research Centre for Freshwater Ecology surveyed the health of the Murray-Darling River Basin and found the environment and biology to be degraded throughout the river system, particularly at the river mouth. This is supported by other research finding the Murray-Darling River is degraded, with vegetation, fish and macro-invertebrate populations in poor condition. A wider survey of 14,000 reaches of rivers by the National Land and Water Audit in 2002 found one third of the reaches have impaired aquatic life and substantially modified nutrient and sediment loads, and 80% of them are affected by catchment disturbance.

Macquarie University researchers reported on the current distribution of 77 species of Australian native butterflies, and the potential changes in distribution of 24 species in response to climate change. They found that even species with currently wide climatic ranges may still be vulnerable to climate change – under a very conservative climate change scenario of a temperature increase of 0.8-1.4°C by 2050, the distribution of 88% of species would decrease and 54% of species distributions would decrease by at least 20%. Under an extreme scenario (temperature increase of 2.1-3.9°C by 2050) 92% of species distributions decreased, and 83% of species distributions decreased by at least 50% (Figure 4.1). Other research at Macquarie University found a moth introduced to Australia to control the Paterson’s curse weed, Dialectica scalariella, showed longer development times, higher mortality and reduced adult weight when fed foliage grown under elevated carbon dioxide conditions.

Figure 4.1 Change in 24 butterfly species distributions in response to a very conservative (top) and extreme (bottom) climate change scenario. (From Beaumont and Hughes, Global Change Biology).