Too late to avoid warming

Too late to avoid warming

Sydney could face an annual temperature rise of up to 4.3 degrees by 2070, and a tripling of the number of days a year when the thermometer soars above 35 degrees, if global greenhouse gas emissions are not cut steeply, a new report has found.

It is too late for the city to avoid a warming of about 1 degree by 2030 as well as a 3 per cent reduction in annual rainfall because of polluting gases already in the atmosphere.

More droughts, fires, and severe weather events, and less rain and snow across the country are also on the horizon, according to the report, Climate Change in Australia, which contains the most detailed and up-to-date climate projections produced by the CSIRO and Bureau of Meteorology.

Its findings, released at the Greenhouse 2007 conference in Sydney this morning, include projections of up to 20 per cent more drought months over most of Australia by 2030.

By 2070 this could rise to 40 per cent more drought months in eastern Australia and 80 per cent more in south western Australia.

The report also spells out the impact that human activity has already had on Australia's climate.

A warming of 0.9 degrees since 1950 and an increase in hot nights have been mostly due to greenhouse gas emissions, it concludes.

These higher temperatures have "exacerbated" the effects of drought and led to a decline in snow cover, including a 40 per cent reduction in snow depth in Spring in the Snowy Mountains in the past 45 years.

Weather patterns and ocean currents have changed, reducing rainfall to south-west Australia and leading to a warming of waters off the east coast of Tasmania that is occurring at triple the global rate of ocean warming.

"The message is that global warming is real, humans are very likely to be causing it and that it is very likely that there will be changes in the global climate system in the centuries to come larger than those seen in the recent past," the report says.

It is based on conclusions of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, released earlier this year, and climate research conducted on the Australian region since the last CSIRO projections were released in 2001.

Co-ordinator of the CSIRO's climate change science program, Paul Holper, said improvements in computer modelling of climate meant the new projections were more accurate than the last ones, which warned national temperatures could rise as much as 6 degrees by 2070.

"Over the past five or six years we have learnt so much more about the atmosphere and the oceans, and our ability to use super computers to simulate climate has improved immensely," he told ABC Radio.

Nationally, temperatures will rise by about 1 degree by 2030, and rainfall will decline by up to 5 per cent, according to the report.

The impact of human activity beyond that will depend on how quickly greenhouse gas emissions are reduced, with worst-case scenarios including a 5-degree warming and a 30 per cent reduction in annual rainfall by 2070.

If carbon dioxide levels can be stabilised at 550 parts per million by 2100, however, the temperature rise in Australia could be kept to about 1.8 degrees by 2070, and rainfall decline to about 7.5 per cent.