Bill Shorten has accused Tony Abbott of “stubborn isolationism” on climate change that could hurt Australia’s international trade in the long term.

Responding to the significant post-2020 greenhouse gas reduction commitments by the US and China, the prime minister said he was “not focusing on what is happening in 16 years’ time” but rather on what his Direct Action scheme might achieve straight away. Australia will have to unveil a similar post-2020 commitment next year.

Citing Abbott’s reaction, the Labor leader said: “I fear it will not be long before this stubborn isolationism takes a toll on our international competitiveness.”

In a speech to the Sydney Institute, he said it was impossible for Australia to “expect the rest of the world to do the heavy lifting on greenhouse gas pollution, while ignoring our inaction”.

“Sooner rather than later, Australia’s refusal to act on climate change will affect our trade negotiations. I would not be surprised if future international trade agreements included a carbon-price equivalent as a mandatory condition.”

And he attacked Abbott’s insistence that the G20 is not an appropriate forum to discuss climate because it should focus on economic issues.

Asked about Australia’s reluctance to discuss climate at the Brisbane meeting, despite the urging of many other G20 countries, Abbott said; “There are lots of venues to deal with climate change … there’s a conference coming up in Lima which will be a climate change conference. There’s a conference coming up in Paris next year which will be a climate change conference. The UN is a forum which is regularly dealing with climate change – that’s as it should be.

“But this is a major economic conference; it is the world’s premier economic conference. And I certainly expect that the focus will be on economic reform, economic growth, how we drive growth and jobs.”

But Shorten pointed out that the US and Chinese presidents had used Apec – also an economic forum – to make their climate policy announcement.

And he accused the Coalition of “abandoning internationalism” when it suited its political agenda.

“It is not good enough to say yes to Iraq, but no to action on Ebola,” he said. “It is not good enough to say yes to free trade agreements, but no to global action on climate change. It is not good enough to attack the unemployed, yet ignore tax havens.”

Australia has been resisting a last-ditch push by the US, France and other European countries for G20 leaders at next week’s meeting in Brisbane to include climate change on the leader’s agenda for discussion, and to back contributions to the Green Climate Fund.

The prime minister has previously rejected the fund as a “Bob Brown bank on an international scale” – referring to the former leader of the Australian Greens.

The fund aims to help poorer countries cut their emissions and prepare for the impact of climate change, and – along with national greenhouse reduction pledges – is seen as critical to securing developing-nation support for a successful deal on reducing emissions at the UN meeting in Paris next year.

As reported by Guardian Australia, Australia has reluctantly conceded the final G20 communique should include climate change as a single paragraph, acknowledging that it should be addressed by UN processes. Australia’s original position was that the meeting should focus solely on “economic issues”.

An early text read “We support strong and effective action to address climate change, consistent with sustainable economic growth and certainty for business and investment. We reaffirm our resolve to adopt a protocol, another legal instrument or an agreed outcome with legal force under the United Nations framework convention on climate change that is applicable to all parties at the 21st conference of the parties in Paris in 2015.”

This has been further negotiated by officials in the leadup to the weekend meeting.

Australia had previously insisted the G20 should discuss climate-related issues only as part of its deliberations on energy efficiency, but the energy efficiency action plan to be agreed at the meeting, revealed by Guardian Australia, does not require G20 leaders to commit to any actual action.

Instead it asks them to “consider” making promises next year to reduce the energy used by smartphones and computers and to develop tougher standards for car emissions.