God and the green movement are battling for the hearts and minds of middle Australia.

As record numbers desert religion, environmentalism is increasingly being used to fill the void, KPMG demographer Bernard Salt said. The green movement advocates ideas such as salvation, damnation and atonement that are similar to those of traditional faiths.

In the five years to the 2006 census, more than 800,000 additional Australians listed themselves as non-believers, making a total of 3.7 million, Mr Salt said.

Environmentalism and religion were similar, he said. “You need to repent now, you need to modify your behaviour now so as to avert damnation.”

Younger people are most likely to claim no formal belief system, but Mr Salt said environmentalism cut across generations.

The Australian Conservation Foundation and Anglican Archbishop of Melbourne, Philip Freier, said many people adhered to religion and environmentalism.