Former prime minister Malcolm Turnbull has likened climate change deniers within the Liberal Party to "terrorists", and argued for a "green new deal" to shift the economy off fossil fuels.

Speaking in Sydney at an event hosted by the Coalition for Conservation, Mr Turnbull and his wife Lucy said Australia should use the "black spring and black summer" of huge bushfires as a "turning point" to take serious climate action.

Malcolm and Lucy Turnbull have spoken out about the need to act on climate change during an address in Sydney to the Coalition for Conservation. Credit:60 Minutes/Channel Nine

"If ever Australians were under any illusion that the consequences of a hotter and drier climate were not real, harsh and dangerous, those illusions have been shattered this summer. These bushfires are utterly without precedent in our history," Mr Turnbull said.

The Turnbulls, who were in south-east Asia during some of the peak of the bushfires, said the effect on Australia's image abroad had been profound.