Emissions blow-out risk as safeguard bid up in the air

The political future of the government's planned safeguard mechanism hangs in the balance as modelling shows its emissions budget is at risk of blowing out.

The Greens and a key crossbench senator have raised concerns about the scheme proposed by the federal government to cut emissions.

Greens leader Adam Bandt has challenged the government to come to the negotiating table on the mechanism with concessions on the proposal, indicating the party would support the measure if new coal and gas projects were stopped.

The concerns over the mechanism coincide with new modelling showing the emissions budget was at risk of blowing out.

The modelling by the firm RepuTex for the Climate Council and Australian Conservation Foundation showed emissions from 16 new coal and gas projects would be about 25 per cent of what the mechanism would aim to reduce.

While companies would be required to reduce emissions by 4.9 per cent each year until 2030 under the mechanism, modelling has shown declines of 8.9 per cent may be needed by the end of the decade to keep within the emissions budget.

The government's proposed mechanism means the emissions of the biggest 215 polluters would be capped.

Companies that breach the limit would be forced to buy carbon offset credits or trade their emissions with other firms.

Mr Bandt said opening coal and gas plants would not allow climate targets to be reached.

"The government is going to need to shift a bit, they want to get legislation through the Senate," he told reporters in Canberra.

"We've offered to compromise on targets, we've offered to compromise on offsets with just one thing: the government stops opening new coal and gas mines.

"The penny does not seem to have publicly dropped with the government, they are still publicly advocating for more coal and gas projects, but that is ultimately just an untenable position."

Independent senator David Pocock said limits needed to be placed on heavy industries offsetting their emissions.

"As it stands, we will join Kazakhstan as the only two countries in the world that allow 100 per cent of emissions to be offset using carbon credits," he told ABC Radio.

"I'm not approaching this with red lines, I want to make sure that this policy is as good as it can be that it will deliver the reductions that we need."

For the mechanism legislation to pass the upper house, the government will need the support of the Greens and two crossbenchers.

Climate Change Minister Chris Bowen said the safeguard mechanism would be critical to reaching the legislated climate target of reducing emissions by 43 per cent by the end of the decade.

"Our reforms will reduce emissions by 2030 by 205 million tonnes, which is very important to achieving those targets," Mr Bowen told parliament.

The Climate Council's head of advocacy Jennifer Rayner said the emissions modelling showed further work was needed to fine tune the mechanism.

Mr Bandt said the modelling reinforced the need to move away from fossil fuel projects.

"Industries like lithium and steel and aluminium should not be asked to do more, because Labor wants to keep opening coal and gas mines," he said.

"We will continue to have discussions with the government to see if we can reach a point where we start to cut pollution in this country."