ACT Environment Minister Simon Corbell said greenhouse emissions would decrease after a peak in 2013 but deferred committing to a 2020 figure until next year.

He announced the goals yesterday as part of the Government's response to a Legislative Assembly interim report into greenhouse gas reduction targets for the territory.

But the Greens and the Property Council of Australia criticised the lack of firm targets.

Greens' environment spokesman Shane Rattenbury welcomed the policy but said a 2020 target was crucial. ''I think these long-term targets are important aspirations but the real measure of a government is what they do over the next five to 10 years because that's going to determine the long-term trajectory,'' he said. The next decade was the ''crunch point''. ''If we don't cut our emissions by 40 per cent by 2020, we'll never achieve those long-term aspirations.''

Canberra emits about four million tonnes of carbon each year and emissions have increased by more than 25 per cent from 1990 levels.

The ACT executive director of the Property Council of Australia, Catherine Carter, said businesses needed a road map.

''Almost 75 per cent of emissions in the ACT come from stationary buildings, so residential homes and commercial buildings. There will be a direct financial cost to anyone who has property of any kind,'' she said.

A greenhouse gas emissions target is one of the items in the Labor-Greens parliamentary agreement, forged after last year's ACT election.

The interim report of the Legislative Assembly made 31 recommendations. The Government agreed in full to 13 recommendations and 16 were agreed to in principle.

The Government did not agree with two recommendations that suggested short-term emissions reduction targets of 5 per cent by 2015 and 40 per cent by 2020.

Mr Corbell said the Government would set a 2020 target by the middle of next year regardless of the outcome of the United Nations climate change meeting in Copenhagen.