Prime Minister Malcolm Turnbull's "courage has deserted him" on climate action, respected former government adviser Bernie Fraser says, predicting the federal Coalition's policies will fail to meet even modest targets to reduce greenhouse gas emissions.

The criticism comes as Senator David Leyonhjelm signalled a crossbench revolt if the Coalition, whose attitude to renewable energy has become more favourable since the leadership change, reneges on a move to ban government investment in wind and household solar.

Mr Fraser, an ex-Treasury head and former Reserve Bank governor, resigned as chairman of the government's Climate Change Authority this month, two years before his tenure was due to end.

Believed to have had a fractious relationship with the Abbott government, he said on Tuesday that Mr Turnbull's climate action rhetoric was disappointing.