THE planet has just five years to avoid disastrous global warming, says the Federal Government's chief scientist.

Prof Penny Sackett yesterday urged all Australians to reduce their carbon footprint.

Australians - among the world's biggest producers of carbon dioxide - were "better placed than others to do something about it", she said.

"Australians can make an enormous contribution, so why would we not rise to this challenge and this opportunity," she told a business conference in Melbourne.

Prof Sackett refused to comment on the failure of the emissions trading scheme to be passed by the Senate this week.

She said her role was as an adviser to the Government and not a commentator on public policy, but she did not deny her appointment a year ago was a political one.

Asked to explain data that showed the earth had been cooling in recent years, the trained astrophysicist acknowledged air temperatures had levelled during the La Nina weather pattern, now nearing an end.

"But next time someone talks about cooler weather, ask them if they are talking about the temperature in the small amount of atmosphere above the surface of the earth or the great mass of heat retained in the world's oceans," she said.

"When scientists talk about global warming, they are referring to the temperature of the whole earth and most of the heat is stored in the oceans, which have not cooled in 10 years."

The professor said even if all the world stopped producing carbon dioxide immediately, temperature increases of 1.3C were unavoidable.

If the earth's temperature rose 2C, she warned, there would be risks that were "difficult and dangerous".

Originally published as We've got 5 years to save world