Tony Abbott has told a G20 leaders’ discussion on energy he was “standing up for coal” as the Queensland government prepares to unveil new infrastructure spending to help the development of Australia’s largest coal mine.

Abbott opened the closed-door discussion on energy on Sunday morning by telling the world leaders that “as the world’s largest producer of coal, I’d like to stand up for coal”, sources told Guardian Australia.

Several leaders, including the French president, François Hollande, made strong statements in support of immediate action on climate change and commitments to the green climate fund, to which Barack Obama pledged $3bn on Saturday. Abbott then wrapped up the climate discussion he had hoped not to have by saying he was glad the leaders had had a chance to discuss energy efficiency.

He remarked that a “good economy is good for the environment” and urged countries to focus on the development of “clean coal” technology and efficient coal and energy use.

After bitter behind-the-scenes discussions and fierce opposition from Australia – as revealed by Guardian Australia – a reference encouraging countries to promise money to funds such as the green climate fund was included in the G20s final communique.

Abbott, who recently said coal was “good for humanity”, also endorsed the mine, proposed by the Indian company Adani, to the meeting.

On Saturday the US president stole the G20 limelight with a hard-hitting speech demanding action on climate change. But Abbott’s comments, as well as Joe Hockey’s insistence on Sunday that global warming did not pose a threat to economic growth, show the Australian government is unmoved by pressure from the G20 leaders on the issue.

The Queensland premier, Campbell Newman, has told his local newspaper he is preparing a major infrastructure announcement to help coal development in the Galilee basin, which has been under a cloud because of the declining coal price.

Newman did not give a figure to the Courier Mail, but the announcement is expected to be made during the visit of the Indian prime minister Narendra Modi, who is addressing federal parliament on Tuesday, and the chairman of the Adani group Gautam Adani.

“We are prepared to invest in core, common-user infrastructure. The role of government is to make targeted investments to get something going and exit in a few years’ time,” Newman told the newspaper.

“It will be open access [infrastructure]. We want a new coal basin to open.”

In an interview from Brisbane with the Indian Express, Adani said the Australian government had given all environmental and regulatory clearances for the $7.5bn coal, rail and port project.

Australia sought to keep climate change off the G20 agenda, and then fought efforts until the last minute by the United States and Europe to strengthen the language in the communique.

Speaking to the media at the conclusion of the event, Abbott emphasised the energy efficiency discussions, adding “all of us support strong and effective action to address climate change ... of course we will all work constructively towards the climate change conference in Paris next year”.

In an ABC interview on Sunday morning, Hockey said climate change was no impediment to economic growth, and downplayed the significance of pledges by the United States and China to cut emissions.

The Labor opposition attacked the government’s handling of the climate issue at the summit.

The Labor leader, Bill Shorten, said Abbott needed to “act like the prime minister of Australia” on such important matters.

“We’ve seen him furiously and desperately behind the scenes ask and shush and hush everyone from talking about climate change but unsurprisingly ... leaders of the rest of the world are determined to act on climate change ...

“It’s now time for Australia to join the rest of the world to face our future honestly and to start taking the necessary steps to ensure that our children and our grandchildren don’t suffer worse damage as a result of us neglecting climate change”, Shorten said.

The Carmichael mine in the Galilee Basin is the one of the largest thermal coal mines in the world, and the largest in Australia. It requires a 388km rail line to a new terminal at Abbot Point.

But the project has been under pressure as coal prices fall to five-year lows.

Adani told the Indian Express a South Korean firm, Posco, had been given the contract to build the railway line and sources suggested the Newman government might be preparing to underwrite the project.

“[Posco] has been given the contract to build the $2.2bn railway network from the pithead in Carmichael to the Abbot Point port,” Adani said.

The director of energy finance studies for the Institute of Energy Economics and Financial Analysis, Tim Buckley, said the Newman government’s plans were “absolutely farcical”.

“I have not spoken to a single person in finance who thinks this can proceed or that it is commercially viable. Eight major international banks have said they won’t go near it,” he said.

Adani says it has already invested $2bn in Australia, but it has no equity here. It bought the rights to the Abbot Point port with loans from a syndicate headed by the Commonwealth Bank and Westpac, and another loan from the State Bank of India.