The government has committed the UK to cut greenhouse gas emissions by 80% by the middle of this century.
Climate Change and Energy Secretary Ed Miliband said the current 60% target would be replaced by a higher goal.
He told MPs the government would not "row back" on green issues in the light of the current economic crisis.
He also warned the big energy companies they face a crackdown on "unfair" pricing policies in his first statement as head of the new department.
Mr Miliband told MPs the government accepted all the recommendations of the report from Lord Turner's Committee on Climate Change.
The target does not include aviation or shipping emissions - but Mr Miliband said they would "play a part" in the government's overall strategy.
It came as European Union leaders agreed to stick to their plan to cut greenhouse gases - despite a surprise demand by Poland and six other member states to drop them to ease the impact on industry struggling with the global credit crunch.
Speaking at the end of a two-day summit, French President Nicolas Sarkozy said: "The deadline on climate change is so important that we cannot use the financial and economic crisis as a pretext for dropping it".
But although all 27 leaders agreed to stick to the aim of cutting emissions by 20% by 2020, Mr Sarkozy acknowledged he faced a tough task in getting a unanimous deal on how to share out the burden of the switch to cleaner energy by the December deadline.
Mr Miliband also stressed the importance of sticking to climate change commitments despite the economic downturn.
He told MPs: "In our view it would be quite wrong to row back and those who say we should, misunderstand the relationship between the economic and environmental tasks we face."
'Tough but do-able'
He said he wanted to achieve a cross-party consensus on climate change, but added: "We all know that signing up to an 80% cut in 2050, when most of us will not be around, is the easy part.
"The hard part is meeting it - and meeting the milestones that will show we're on track."
Mr Miliband also announced that the government was ready to legislate to force energy companies to introduce fairer pricing for customers with pre-payment meters if they would not do so voluntarily.
He also signalled new help to encourage small-scale electricity generation though technology such as home-based solar panels and wind turbines.
He told the Commons the Energy Bill would be amended to introduce a "feed-in tariff" to guarantee prices for micro-generation projects which are able to supply electricity to the national grid.
Speaking later to BBC News, he said the 80% target was "tough but it is do-able" and could be met through measures including renewable fuels, nuclear power and individuals "doing things differently".
He said changes to the climate were "happening much quicker than we anticipated or even feared a few years ago" and it was "right to step up the pace".
"Our children and our grandchildren will really not thank us if we just carry on and let this problem get worse. The costs that they will face will be all the greater if we do that," he added.
In a letter to Mr Miliband, Lord Turner said the tougher target would be "challenging but feasible", and could be achieved at a cost of 1% to 2% of GDP in 2050.
He also said a cut of 80% on 1990 levels by 2050 should cover all the major greenhouse gases - not just carbon dioxide - and all sectors of the UK economy, including shipping and aviation.
But because of practical problems in allocating emissions of international transport to the UK, they should not be included in the Climate Change Bill's five-yearly carbon budgets, he said.
Instead the overall target should be "at least 80%", with greater reductions in sectors covered by the bill if aviation and shipping did not make sufficient cuts by the middle of the century, he said.
But Lib Dem climate change and energy spokesman Steve Webb said Mr Miliband's decision not to include aviation and shipping in the 80% target made a mockery of his commitments.
"It's like telling everyone you're going on a calorie-controlled diet but not counting cream cakes.
"As we saw when the government gave the green light for Stansted expansion, there is a huge gap between what ministers say on climate change and what they actually do."
Shadow climate change secretary Greg Clark, for the Conservatives, welcomed Mr Miliband's announcements.
He said: "The choice between aggressive and ambitious action on carbon reduction and a successful, powerful economy is, in fact, not a choice at all - they are one and the same."
Mr Miliband's statement was also welcomed by environmental campaigners, including the RSPB, World Development Movement, WWF and Christian Aid.
Friends of the Earth executive director, Andy Atkins, said his group was "absolutely delighted" but added: "We cannot leave the cuts in aviation and shipping emissions to chance.
"The government must listen to the concerns of the public and majority of MPs who want to see a law that covers all the UK's emissions."
But the National Housing Federation warned that unfair energy pricing would continue under Mr Miliband's plan.
A spokesman said: "It is excellent news that Ed Miliband has quickly come to the conclusion that the prepayment meter rip off is unacceptable.
"But even with the measures he envisages, prepayment meter customers will still pay as much as £88 more than others - as Mr Miliband seems to have accepted the argument by the energy regulator Ofgem that a premium for maintaining the meters is acceptable."