German Chancellor Angela Merkel, whose country holds the rotating EU presidency, said the agreement reached at a summit in Brussels on Friday would usher in a new era in the fight against global warming.

"It has been possible to, as it were, open the door to a new dimension of European cooperation for years to come in the area of energy and combating climate change," Merkel said.

The accord's overarching achievement is to commit the 27-country bloc to reduce carbon dioxide emissions by 20 percent by 2020, when compared to 1990 levels.

The pact also obliges member countries to make renewable energies, such as solar and wind power, the source of 20 percent of the total energy consumption on average across the EU by 2020.

"These are a set of ground-breaking, bold ambitious targets for the European Union," said British Prime Minister Tony Blair, who pushed hard for a climate agreement. "It gives Europe a very clear leadership position on this crucial issue facing the world."

Each according to its ability

The talks in Brussels had broken up overnight during the two-day conference with divisions over setting a "binding" target for the use of renewable energy sources. The leaders, however, agreed on a compromise that accords member states some flexibility in meeting national goals.

Countries like Poland and the Czech Republic are heavily dependent on carbon energy sources such as coal and had complained that the binding renewable energies target was overly ambitious and prohibitively expensive. France, on the other hand, had insisted on including nuclear energy among the list of environmentally friendly options.

To bring the opposing states on board, the agreement stressed that "differentiated national overall targets" would be set, "with due regard to a fair and adequate allocation" taking into account the potential of each member state.

Thus, those countries whose exploitation of renewable energies is already well advanced would take up the slack left by the others to ensure the overall wide target is met across the bloc.

Leverage against non-EU polluters

Merkel said the pact gave her a mandate to press major world polluters into action, as the EU would offer to reduce emissions of the gases that cause global warming by an additional 10 percent by 2020 if those countries would do so as well.

"We are going into negotiations offering 30 percent if international partners are prepared to go along with that, so it is a genuine offer in what is an extremely important topic for the whole of humanity," she said, adding that it would be "a bad signal" to the rest of the world if Europe did not stick to the deal.

But tough questions must still be answered in Brussels.

The European Commission has been set the task of working out how much of the renewable energy burden each state will have to bear; a cumbersome, deeply technical and controversial task that it hopes to complete in the autumn.

Environmental nitty-gritty

"It will be a huge job, huge job from a legal and a technical point of view," acknowledged European Commission President Jose Manuel Barroso. "I have assured them that we will do this in all fairness and seeking the acceptance of each member state on these objectives."

Swedish Foreign Minister Carl Bildt said there was no one-size-fits-all solution.

"Different nations have different conditions," he said. "For instance, we can easily meet the renewable target in Sweden -- in fact we are above it. But others are having substantial difficulties."

Nuclear power part of pact

The accord represents a minor victory for France by having nuclear power -- which meets some 40 percent of its total energy needs -- recognized as one way to reduce carbon dioxide emissions.

The agreement noted the Commission's assessment of the contribution of nuclear energy in "meeting the growing concerns about safety of energy supply and carbon dioxide emissions reductions."

However, it also highlighted safety concerns, stating that "nuclear safety and security" should be "paramount in the decision-making process."

Barroso said he believed the final agreement comprised "the most ambitious package ever agreed by any institution or any group of countries" to combat climate change.

Green groups want more

It was unclear if the deal would provide for sanctions against nations that fail to meet their climate change targets.

Environmental protection group WWF said the EU deal set the "right path" to control global warming but warned that the EU must put in place laws and measures so that the goal does not remain "hot air."

"It is clear that the targets decided today will only be achieved with solid laws, measures and incentives," WWF's Stephan Singer said, adding that the targets need to be translated into a shift of investments towards green technologies, rather than to nuclear power stations.