Britain must abandon using almost all fossil fuels to produce power in 20 years' time, the government's climate change watchdog will warn today.

The independent Climate Change Committee will publish its advice to the government that the UK should set a 2050 target of cutting all greenhouse gas emissions by at least 80% - including the emissions from aviation and transport, which were previously excluded.

Because it is unlikely that emissions from aviation and shipping will be cut so dramatically, other sectors, particularly power generation, would have to reduce emissions by much more, with big increases in energy efficiency, wind and tide power, and probably new nuclear generators, Lord Turner of Ecchinswell, the committee chairman, told the Guardian.

"We have to almost totally decarbonise the power sector by 2030, well before 2050," he said.

The committee will say the far-reaching changes would cost about 1-2% of the value of the economy in 2050, although growth would still be strong. "Rather than be twice present levels, [gross domestic product] would be 1 or 2% less than that," added Turner.

In his speech to the Labour party conference last month, Gordon Brown hinted that the government would accept the new target when it responds, possibly within days, although it is not clear if it will accept the full report.

Last night Ed Miliband, the new energy and climate secretary, said he welcomed the report. "We need to act now to avoid dangerous climate change and the action we take must be guided by experts. This is a pressing issue and we'll respond to the recommendations swiftly. The hard work will be for us all to make emission reductions a reality over the coming decades."

If the report is accepted in full, campaigners said the UK target would be the most ambitious legally binding commitment of any country and would give the UK a strong position in international negotiations about a new global plan.

"It would mean finally the government would accept the advice of scientists," said Martyn Williams, climate change campaigner for Friends of the Earth. "We could say to people in international negotiations: you can do what we're doing, not just what we're saying."

However, Williams warned that in future the commitment to include aviation and shipping must also be made legally binding. "If the government [did] not accept a mechanism to make sure they and other governments were held to account, then we'd have to wonder if there was any confidence it would have to be delivered," he said.

The Climate Change Committee was set up by the climate change bill and was asked to advise government on whether to increase the target of a 60% cut in carbon emissions by 2050.

Today's report will say the new target must be "at least 80%" and extend it to include other greenhouse gas emissions such as methane and nitrous oxide. International aviation and shipping should not be part of the legally binding interim "budgets" that the committee will report on each year but should be a national target, and would "absolutely end up with an equal level of scrutiny", said Turner.

In the first decade the biggest change would be a big expansion of energy efficiency and in the second decade of renewable energy. Such a "radical" change was "do-able" but could also require new nuclear power, and carbon capture and storage (CCS) technology for coal-fired power stations and industries like cement and steel, both of which will be seen as controversial by environmental campaigners. "It's possible to do it while knocking out particular technologies [like nuclear or CCS], it just gets significantly costly and more difficult to do," said Turner.

Longer term, zero-carbon electricity would also have to be used to power cars and heat homes, says the report.

The report will increase pressure to abandon controversial plans for new coal-fired power stations in the UK before CCS is available at that scale. Ministers have previously admitted full-scale CCS might not happen before 2050. Turner said the committee's opinion would be published in a more detailed report in December.

The December report will also recommend interim targets up to 2022 and the impact of different industry sectors.