New Greens leader Richard Di Natale has vowed to get climate change policy "back on track" and champion "mainstream progressive values" after the surprise resignation of Christine Milne.

But the appearance of smooth generational change to an unopposed Senator Di Natale was diminished by claims the transition was orchestrated to thwart any bid by Senator Milne's deputy, Adam Bandt, to assume the top job.

Senators Milne and Di Natale repeatedly refused to be drawn on assertions that he and new deputies, Scott Ludlam, from Western Australia, and Larissa Waters, from Queensland, had been given advance warning of Senator Milne's decision to end her 25-year political career.

Fairfax Media understands that Mr Bandt expressed his annoyance that he was not given the opportunity to canvas support before the vote was called within 90 minutes of Senator Milne informing Greens senators of her decision at a party room meeting on Wednesday morning.

The senators had been called to Canberra ostensibly to discuss their approach to next Tuesday's federal budget and to support Senator Milne when she addresses the National Press Club on Thursday.

Senator Di Natale played down complaints about the process, telling reporters it was identical to when Bob Brown stepped down three years ago: "Someone may have been disappointed with the outcome. Surprise, surprise. That's politics, right?"

Mr Bandt, the only Green in the House of Representatives, also refused to be drawn, tweeting: "Congrats Richard & new team! V happy to hand over Deputy to focus on new baby (due in few wks!) & winning further Reps seats in Vic & NSW."

Senator Di Natale's elevation signals a more pragmatic leadership approach, with the 44-year-old former GP repeatedly saying he wanted to "get things done" and was willing to re-visit issues.

"There's an opportunity with the new leadership to talk about a whole lot of things. I'm not going to do things on my own," he said.

Senator Sarah Hanson-Young, the party's high-profile spokesperson on immigration, described his elevation as a "massive opportunity to re-shape how we engage with the community to put us on a strong path to winning more seats at the next election".

Tony Abbott and Bill Shorten paid generous tributes to Senator Milne, who was elected to the Tasmanian parliament as an independent in 1989, became the leader of the Greens in that state in 1993 and the Federal Parliament's most unflinching advocate of action on climate change after becoming a senator in 2005.

The Prime Minister described her willingness to serve as testament to her commitment to Australia. "Even though we have far more often than not been on opposite sides of most political arguments, I respect her commitment [and] we've always had good and cordial relations," he said.

Mr Shorten concurred. "I haven't always agreed with every policy she has had or every position she has taken, but I can certainly respect the conviction and passion which she has taken to advance her issues and I congratulate her on two and a half decades of distinguished public life."

Defence Minister Kevin Andrews was not so gracious, tweeting: "Does it really matter who will lead the freedom hating @Greens? Their anti-family & community destroying policies remain."

While Senator Di Natale said the Greens would be challenging the government on issues from health and education to public transport, he said: "If we do not address climate change as a nation and as a planet, well then everything else is sort of redundant, isn't it?"

He said he was keen to talk to Mr Abbott, but played down the prospect of an accord: "I'm going to talk to him and see if there are areas where there is common ground. Sadly, I think there aren't many."

Senator Milne, who will turn 62 and become a grandmother this year, said she felt it was "absolutely the right time" to be retiring from Parliament, but insisted she would remain active on climate change. She also indicated she would be departing before next year's election.

Senator Di Natale, a former VFA footballer with Coburg and Oakleigh, keen surfer and the son of Italian migrants, made it clear he would not be changing his plain-speaking approach to politics.

"I think people are sick of the sort of the nonsense that goes on in this place and, you know, if they want someone who is not going to play the game in that way, well great! And, if that doesn't work out well, I'll go back to growing some veggies at home."

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