An Environment Department source said the greenhouse trigger would be proposed by a panel of five independent experts in a discussion paper next week as part of an official review of Australia's national environmental laws. The trigger would be "interim", and would be removed if an emissions trading scheme started in Australia.

The proposal would automatically refer large projects which emit high amounts of carbon for an environmental assessment by the office of the Environment Minister, Peter Garrett.

The official review, which reports its final recommendations in October, is headed by the former ANU chancellor Alan Hawke. It is not yet known how the trigger would fit into the existing laws if eventually accepted by Mr Garrett, and the cabinet.

The national laws, called the Environment Protection and Biodiversity Act, review industry and residential developments that could adversely affect the "national significant environment", such as endangered species and national parks.

The prospect of an Australian greenhouse trigger was raised as a recommendation in a March Senate committee report into the national environmental laws who recommended it should be considered "in the light of" the national review and the emissions trading scheme.

The Government's carbon trading legislation remains stalled in the Senate after the Opposition yesterday began delaying the vote by passing several motions, disrupting Senate procedures and speaking for long lengths of time in the debate.

The Opposition also lost a motion to "reorder" the Senate business to give the emissions trading scheme a lower legislative priority. However, Independent Nick Xenophon will change his vote today when the same motion is put up again by the Opposition if the Government does not agree on a new Senate timetable.