The coalition's net zero assumptions rely partly on using developments in soil carbon to support broader emissions offsets.

Soil carbon storage is one of the priorities identified in the government's "technology roadmap", saying it will get Australia 40 per cent of the way to net zero emissions.

It suggests landholders could earn around $400 million through the sale of accredited soil carbon sequestration in the middle of the century.

The government is also relying on broad domestic and international offsets to reduce emissions by another 10 to 20 per cent.

Intergovernmental Panel on Climate Change vice-chair Mark Howden warned a reliance on soil carbon to cut emissions was risky and problematic as the climate warms.

"With soil carbon, as things get hotter and drier, which is the prediction for southern Australia, then the soil carbon is likely to go down," he told AAP.

"So if you're relying on carbon sequestration, from a policy perspective, (it) may actually be problematic and risky."

The Australian National University's climate change institute director does not think domestic policies sufficiently factor in the risk of soil carbon being rendered significantly less effective.

How degraded soil carbon becomes depends on the rate of warming.

"I could say with strong confidence that if our rainfall goes down and our temperatures go up, we will lose soil carbon from those landscapes," he said.

"That would only be countered by potential activities that might increase soil carbon."

Australian Associated Press