Research by the Australian Bureau of Meteorology and the CSIRO has found that bushfire seasons will start earlier, end slightly later and become more intense in coming decades.

A climate study of south-east Australia by the agencies in 2007 found the number of days with "very high" or "extreme" fire danger ratings would increase significantly. The worst changes were predicted for northern NSW.

By 2020, days of extreme fire danger are forecast to increase by 5 to 25 per cent if climate change is low and by 15 to 65 per cent if it is high.

An author of the report, Kevin Hennessy from the CSIRO, told the Herald yesterday: "There does seem to be a human element to bushfire risk. In terms of human contribution it is clear that most of the global warming since about 1950 is likely due to increases in greenhouse gases. Higher temperatures clearly increase the risk of bushfires."

Professor Mark Adams, dean of the faculty of agriculture at the University of Sydney, said higher levels of carbon dioxide in the atmosphere had increased the risk of bushfires and added to the likelihood that their intensity would also increase.

"I think the immediate concerns outweigh the longer term issues such as an increased incidence of fire days and their severity," said Professor Adams, program leader at the Bushfire Co-operative Research Centre.

"Here in Australia fires are probably the thing that needs to be very high on our priorities list when we are concerned about possible effects of climate change. We are just facing a very dangerous decade or decades as our ecosystem recalibrates to the new climatic conditions."

Professor Adams said there was not enough evidence to conclude whether climate change had already begun affecting the number and severity of fires.

"We don't have the evidence to test those assertions. We cannot do anything about the weather in the short term. The only things we can manage in relation to climate change and fire risk now is on the ground, such as management options and reducing fuel use, keeping fire trails clear and having adequate numbers of people to run planned fires."

The Greens leader, Bob Brown, said climate change was not necessarily the cause of bushfires but was "making them worse, making them more intense, more destructive and more extensive".

"The predictions on climate change are for worse bushfires with greater intensity as we go down this century. That means that if we are looking to minimising these tragedies in the future we very much have to turn around this catastrophic potential of climate change and take action now in our own time."

Senator Brown said the Government should set up an international wildfire centre and take a tougher stance towards people who light fires on days of extreme risk.

"These fires are occurring with increasing frequency around the planet - witness the fires in Greece and California, Spain and Portugal, in recent times. I think most Australians would be in favour of … trying to work out how best we can prevent infernos like we have seen yesterday and continuing today.

"We have to look at laws that make it easier to have people who light fires in periods of extreme fire danger to be not only caught but to be prevented from doing it again."