The draft climate change bill published this week recommended that an expert committee explore whether the target should be revised.
The committee could also look at the impact of other greenhouse gases and international aviation and shipping emissions, while five-yearly carbon budgets may be introduced.
But Friends of the Earth director Tony Juniper said: "It is ludicrous that the government intends to set the UK carbon budget for the next 15 years based on targets that are under review."
The Green Party added that the bill should set binding targets to cut at least six per cent a year. WWF-UK said there should be an 80 per cent cut by 2050 and argued that excluding aviation will undermine the bill.
Meanwhile, the Commons environmental audit committee this week urged the government to identify areas that could suffer climate change impacts such as flooding by 2050. This should be used to inform planning policies, particularly for major housing growth, it said.
The committee also recommended that a specific secretariat should be appointed to co-ordinate the climate change programme. The government should investigate climate change skill and knowledge gaps across its own departments, the report adds.
The draft climate change bill is available at PlanningResource.co.uk/doc.