Politicians are getting away with flagrant dishonesty as a shift from fact to opinion colours the political debate around climate change, former Liberal leader John Hewson says.

Key points: There's a a lack of evidence in public debate, John Hewson says

There's a a lack of evidence in public debate, John Hewson says He says politicians either ignore climate change or attempt to use issue to score points

He says politicians either ignore climate change or attempt to use issue to score points Australia has reached a point where facts are of lesser value than opinions, he says

Dr Hewson was speaking in the run-up to today's Global March for Science, with gatherings taking place in 12 Australian cities and towns as well as in Washington DC and other centres worldwide.

He told AM he initially decided to get involved because he was concerned about the "the lack of evidence being used as the basis of public policy".

"I think science is probably more useful and more relevant to society today than it's probably ever been. But there's been a widening gap between science and the public," he said.

"We see science funding being cut. We see, obviously, a lack of evidence in public debate. We see attacks on scientists, as we've seen in the climate change debate.

"And I think we need to stop and recognise the significance of science and the importance of funding it properly and using the evidence that it produces as the basis of good public policy."

He said climate change was the most significant challenge faced by society today, but said politicians were playing politics with it.

"Our political process basically plays short-term politics with it, ignores it when it wants to, scores points on it," he said.

"None of us would know that climate was an issue if the scientists hadn't told us. You can't look out the window and see it's a problem.

"It's non-climate scientists, for example, have to take the word of the scientists. So it's easy for a small group to play politics.

"People like John Howard in the past have admitted that they did deliberately play short-term politics and they remain an agnostic when it comes to climate. But you know, it's not a question of religion. It is a question of science and scientific fact."

Asked if Australians were seeing "more flagrant dishonesty" from their politicians", he said "yes".

"Often people say to me in the business community, for example: 'We can go to jail for false and misleading behaviour. We have truth in advertising laws. How come they don't apply to politics?'

"It's a pretty good question because of the extent to which we have got to this post-truth, fake news world.

"There's a very significant shift, I think, away from fact to opinion. You make up your own facts to back your argument. You quite often see that in public debate.

"The whole debate has become seriously distorted and misrepresented. And so, it's a bit of a plea, really — let's go back to the evidence.

"Let's go back to the significance of science in schools, in education, in funding it properly, in recognising the value of it — the contribution that it can and should make to our society."