The UK must cut its greenhouse gas emissions by at least 34% by 2020, the committee set up to advise the Government on climate change has recommended.
The Committee on Climate Change, chaired by Adair Turner, also said emissions should be cut by even more if an international deal on reducing greenhouse gases is agreed.
If the current UN negotiations lead to a new deal on climate change in Copenhagen next December, the UK's greenhouse gases should be cut by 42% on 1990 levels by the end of the next decade.
The significant reductions can be achieved at a cost of less than 1% of GDP in 2020, and using existing green technologies, a report from the committee said.
But stronger Government policies will be needed to move the UK to a low-carbon economy.
The cuts can be achieved by cleaner power generation from sources such as wind, which could make up 30% of the UK's electricity by 2020, and measures including energy-efficiency improvements in homes and offices and developing more efficient, electric and hydrogen-powered cars.
The report said nuclear power could play a role in low-carbon electricity generation, and did not rule out new conventional coal-fired power stations in the next decade.
It recommended the Government should make clear that fossil-fuelled power plants which do not have technology to trap and permanently store carbon emissions should not be allowed to generate electricity beyond the early 2020s.
New coal-fired power stations should only be built with the "clear expectation and certainty" that they should be retrofitted with carbon capture and storage (CCS) by the early 2020s, Lord Turner said.
The climate change committee, set up under the Climate Change Act, has already recommended a cut of 80% on 1990 levels by 2050 - advice which has been accepted by the Government.
