Tony Abbott has given his strongest indication that he would sooner fail to meet Australia's emissions reductions target than spend more money on his climate change policy.

The Opposition Leader was asked on Saturday whether he was prepared to spend more money to honour his promise to cut Australia's greenhouse gas emissions (on the levels they were in 2000) by 5 per cent by 2020.

Estimates by Treasury and independent modeling companies suggest that the Coalition's Direct Action funding will fall several billion dollars short.

''If it comes down to it,'' a journalist asked Mr Abbott, ''and you need to spend several billion more than you budgeted, which do you do? Do you let the targets slip out or spend more money?''

Mr Abbott replied: ''I want to just say of our Direct Action policy that it's funded, it's costed and it's capped.''