The UK has been asked to significantly reduce its greenhouse gas emissions and boost renewable energy within 12 years.
The aim is for 20% of EU energy to come from renewables by 2020
As part of a wider European Commission plan to cut overall emissions by 20% by 2020 - Britain has been asked to reduce its share by 16%.
And it has been given a target to make renewable energy account for 15% of all UK energy. In 2005 it was just 1.3%.
The final targets are still subject to negotiation. The government said the UK would play its part "in full".
On Wednesday European Commission president Manuel Barroso announced plans which he hopes will make Europe "the first economy for the low-carbon age".
Total energy mix
The aim is to cut the EU's total greenhouse emissions by 20% by 2020 - and plans include extending the Emissions Trading Scheme to include more industrial sectors from 2013.
Richer nations like Britain and Denmark were told to cut emissions, while poorer countries like Bulgaria and Romania will be allowed to increase them.
And each country was given a target for the percentage of its total energy mix to come from renewable energy, like wind and solar power.
At 15% the UK target is lower than the EU average, but means it would have to achieve the biggest increase of any country - because it is starting from such a low base.
But there will be a new trading scheme for renewable energy certificates so Britain could buy in extra renewable power from other member states.
Environment Secretary Hilary Benn told the BBC: "The increase in renewables is going to be a big step up from where we are now, but we are confident we can do it - we're going to have to work very hard on it."
He said a tidal barrage across the River Severn - a feasibility study into which was announced on Tuesday - could supply 5% of Britain's electricity while plans for the world's biggest offshore wind farm, the London Array, had been formally approved.
Business Secretary John Hutton said a major review of Britain's domestic climate change strategy was under way and Britain was committed to meeting its share of the EU's target for boosting energy from renewable sources.
But he said the final figure was still to be determined in negotiations between ministers.
"Whatever the final outcome, the UK is already exploring a vast expansion of wind energy offshore, and tidal power on the Severn, and we are already thoroughly reviewing our strategy to drive progress further," he said.
He added that it was important to agree the plan as soon as possible to give businesses confidence in planning low carbon investments.
Maria McCaffery, head of the British Wind Energy Association described the plans as "a revolution for the UK's energy supply" but said it would require a "step change" in government policy.
"Wind energy is the next North Sea Oil. Britain could be a world leader in renewable energy if we have the will to make this vision a reality," she said.
Chairman of the Engineering Employers' Federation, Martin Temple said he was relieved that Mr Barroso had said energy-intensive industries would be give emission allowances free of charge.
Mr Temple said: "Our concern has always been that if a badly-designed Emissions Trading Scheme forced European companies to incur extra costs this would damage our competitiveness and increase emissions by forcing companies to relocate elsewhere."
The UK challenge to cut greenhouse gas emissions by 16% applies to sectors of business and industry which are not already covered by the Emissions Trading System for big businesses. The UK's overall cut should be higher than 16%.