Australia's greenhouse gas cut targets quietly tripled on Saturday night, from a 5 per cent cut by 2020 to a cut of more than 18 per cent.

The failure of the federal government to repeal the carbon price has triggered a far more ambitious emissions reduction target.

Environment minister Greg Hunt. Credit:Alex Ellinghausen

As of midnight May 31, the Clean Energy Act 2011 passed by the Gillard government sets a default target that is more than triple the previous 5 per cent goal.

Under the existing legislation, the government of the day was supposed to have decided on an emissions cap to enable the start of a carbon emissions market in 2015. Since no cap has been set, a default target is automatically generated.