The former federal Greens leader led the stop-Adani convoy that began in Hobart just before Easter and travelled to Clermont in central Queensland before reaching its final destination in Canberra on Sunday where a rally was held on the lawns of Parliament House.

Organisers estimated there were 2,500 people at the rally - "a bigger crowd than Bill Shorten will face today and a bigger crowd than Scott Morrison will ever face", Dr Brown said.

He told the crowd that neither of the big parties were willing to stop the Adani mine to secure the planet for Australia's kids.

"There will be no divine intervention, it is up to us," he said to applause from the crowd.

Dr Brown's appearance came after a line of supporters addressed the rally, including songwriter Paul Kelly who sang 'My Island Home'.

Booker prize-winning Australian author Richard Flanagan said he was prepared to blockade the Adani site.

"I'll be there," he said to cheers from the crowd.

Dr Brown told reporters the convoy had been peaceful and law abiding but participants had endured hardships along the route.

"We had rocks thrown at us, we had people spat on, some people were actually physically absued."

A fake Scott Morrison and Bill Shorten received boos from the audience as they went on stage to brandish posters like 'ADANI COAL MINE? YES!'

In contrast, supporters, wearing their black and red Stop and Adani tee shirts, carried banner reading: 'We are here for our grandchildren ... and the world'.

Greens leader Richard Di Natale told reporters Australia was in the midst of a climate election.

"Right now the Adani coal mine is a test of whether Liberal or Labor are serious about stopping climate change and right now," he said,

"Liberal and Labor have failed the test."

However, he said the Greens wanted to negotiate with a new Labor government and "turf this lot out", he said referring to the Morrison government.

Meanwhile, the major parties continued to bicker over their own climate policies.

In Brisbane, where Labor was holding its campaign launch, Mr Shorten said there was a clear choice at this election.

"You can have cowardice and chaos on climate change or courage and action," he said.

But Treasurer Josh Frydenberg said climate change shouldn't be seen as a binary choice between doing something and doing nothing.

"We're taking action. But what Bill Shorten has failed to do is come up with realistic targets, costed policies and practical solutions," he told ABC television's Insiders program.

"He has been very tricky. He has failed to answer the obvious question 63 times - what is the cost to the economy on the policy?"

Australian Associated Press