He says the government will only achieve 60 per cent of its target for 2020, which was to reduce its emissions from 1990 levels by 150 megatonnes.
Miller says one of the reasons for the shortfall is the increased reliance on natural gas to generate electricity.
He says in his report that could increase emissions by four to 16 megatonnes, depending on factors like the weather.
He says the governing Liberals should use their review of their long-term energy plan to make sure they're keeping their targets in mind.
Miller also says they should be paying more attention to the fight against climate change because there's been little progress this year.