Greens leader Richard Di Natale says Bill Shorten will almost certainly be Australia's next prime minister and promises to hold him to account in the Senate over climate change.
Dr Di Natale made the comments in Perth while announcing a plan to move thermal coal industry workers into renewable energy jobs.
He suggested the Greens were Labor's most reasonable option for cooperation in the upper house.
"At this stage, it looks highly likely that we will see Bill Shorten as the next prime minister of this country," Dr Di Natale told reporters on Tuesday.
"But if he is to deliver his agenda, who is he going to be negotiating with in the Senate? The Greens will hold him to account, push the Labor party further on climate change.
"Or is it going to be Bill Shorten talking to Pauline Hanson or Cory Bernardi?"
Dr Di Natale said voters were desperate for serious climate change policies.
"Neither party has a plan to transition out of coal," he said.
"We've got two parties stuck in the past, we've got this embarrassing debate about electric vehicles. I mean this is wacky stuff, it is bonkers."
Australian Associated Press