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.
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.
Greens leader Christine Milne said the measure was inserted in the act to insure against ''a government like this refusing to set a cap''.
''It won't have realised because it never put its mind to the detail,'' Senator Milne said. ''By doing nothing more than we are already doing, we are getting to 18.8 [per cent] and if we put a bit of effort in, we can go even higher.''
A spokesman for Environment Minister, Greg Hunt, declined to confirm the government had overlooked the default.