Greenhouse gas emissions need to be reduced far more quickly than was previously thought, says a climate change research institute.
A report by the Tyndall Centre said a UK government target of a 60% cut in emissions by 2050 is insufficient and needs to be 70% by 2030.
But it requires a major programme of action within the next four years.
It also calls for a climate change bill to commit ministers and business to making the target a reality.
Kevin Andersen from the Tyndall Centre for Climate Change Research, based at the University of Manchester, said the government had no time to waste.
"For the UK we've seen emissions in carbon dioxide going up year on year since 1990 and we don't envisage an immediate change in that trend.
"The government needs to set some policies in train now and I literally mean now within the next few months so that say by 2010/2012 we have reversed our current growth in emissions and we then start to see very significant reductions year on year for the next 20, 30 and 40 years.
"We need this if we are to make our fair contribution."
The study was commissioned by Friends of the Earth and the Co-op Bank.
Signal
A Friends of the Earth spokesman said the 70% target could be achieved through technology such as solar power, wind energy and biofuels.
The former energy minister, Brian Wilson, said the government should set up a separate department to tackle these challenges.
He said: "Why is there no signal from government that this is the greatest policy imperative of the 21st Century?
"Why is there not a department of energy and carbon reduction?"