More droughts, more flooding rains for Australia

by Dr Peter Whetton, CSIRO DAR

Australia will be hotter and drier in coming decades according to CSIRO's latest climate change estimates. "Rising concentrations of greenhouse gases are the culprit," says Dr Peter Whetton from CSIRO Atmospheric Research.

In 2001. CSIRO released these projections regarding the likely extent of climate change in Australia and the expected impacts across the country."Warmer conditions will produce more extremely hot days and fewer cold days," says Dr Whetton.Over most of the continent, annual average temperatures will be 0.4 to 2°C greater than 1990 by 2030. By 2070, average temperatures are likely to increase by 1 to 6°C. The temperature ranges quoted indicate the scientific uncertainty associated with the projections.

"The warming won't be the same everywhere," he says. "There will be slightly less warming in some coastal areas and Tasmania, and slightly more warming in the north-west." South-western Australia can expect decreases in rainfall, as can parts of south-eastern Australia and Queensland. Wetter conditions are possible in northern and eastern Australia in summer and inland Australia in autumn.

In areas that experience little change or an increase in average rainfall, more frequent or heavier downpours are likely. Conversely, there will be more dry spells in regions where average rainfall decreases."We may also see more intense tropical cyclones, leading to an increase in the number of severe oceanic storm surges in the north. Rises in sea level would worsen this effect," says Dr Whetton.

Sea level is likely to rise at a rate of between 0.8 and 8.0 cm per decade, reaching 9 to 88 cm above the 1990 level by the year 2100."Evaporation will increase over most of the country. When combined with changes in rainfall, there is a clear decrease in available moisture across the country," says Dr Whetton.

Changing climate is likely to have a profound effect on Australia, with many winners and losers.

"A better understanding of the likely impacts of climate change can contribute to adaptation strategies designed to minimise adverse impacts and optimise benefits," says Dr Whetton. "Natural ecosystems most at risk are coral reefs, alpine ecosystems, mangroves and wetlands. Also under threat are tropical forests, savannas, deserts and native grasslands. "Natural systems have little opportunity to adapt to climate change. Higher temperatures and lower rainfall will be a threat. Climate change and sea level rise will add to the vulnerability of many of Australia's wetlands."

Higher carbon dioxide concentrations will increase plant productivity and the efficiency with which plants use water. A moderate rise in temperature will increase plant growth in temperate areas but may reduce it in the north. Warmer conditions will reduce frost damage to many crops. However, fruit trees need cold weather to set fruit, so some fruit yields may decline. Wheat yield will rise with warmer conditions if rainfall doesn't change. A rainfall decline of 20 per cent with temperature increases of more than 1°C will lower yield.

"The net effect on agriculture will be a trade-off between the positive impact of higher carbon dioxide and the negative effect of lower rainfall and higher temperatures," says Dr Whetton. Forests will benefit from a carbon dioxide-enriched atmosphere, but gains may be offset by warmer conditions. "Some tropical pests, like the Queensland fruit fly, may spread southwards. Other temperate pests, like the light brown apple moth, may move to cooler areas," says Dr Whetton. "We're also likely to experience more water shortages and less snow."

CSIRO scientists contribute to the Intergovernmental Panel on Climate Change, which is the international group charged with assessing the latest science on greenhouse. CSIRO's new projections incorporate IPCC findings. CSIRO issued its last climate change projections in 1996. These new projections suggest a greater temperature increase than was proposed in the past. Rainfall changes are similar in direction but greater in magnitude than those released five years ago.

May, 2001
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