EU leaders today agreed to combat climate change by ordering 20% of Europe’s energy mix to come from renewable sources by 2020.

The agreement is being hailed as “landmark” deal and a breakthrough by politicians and the green lobby alike, came ahead of a crucial EU summit on Thursday, at which 27 prime ministers and presidents aim to finalise the ambitious package to slash greenhouse gas emissions by 20% by 2020.

The agreement was reached this afternoon in negotiations between government officials from across the union, the European parliament, and the European Commission paves the way for a new law obliging all EU countries to meet national targets for renewable energy.

Two contentious points had threatened to derail the legislation – the insistence that biofuels comprise 10% of transport fuel by the 2020 deadline, and an attempt by Italy to loosen the law by ordering a review of renewable energy progress in 2014. The review date was retained, but the compulsory nature of the overall target and the national quotas also survived.

The 10% biofuels target was retained, despite serious misgivings about their current development, but the equation was changed to include cars and trains running on electric power while the European Commission is to report within two years on the impact on land use of biofuels and on their “sustainability.”

To count towards the 10% quota, the biofuels used in the transport sector must save a minimum of 35% of greenhouse gases compared with their fossil fuel equivalent.

Experts also argue that using the crop-based products as a petrol or diesel substitute is also misplaced as much greater energy savings can be had by, for example, heating buildings with biofuels.

Greenpeace, usually a fierce critic of the EU climate change policies, described the agreement as a “landmark.”

“A ray of light amid the gloomy stone age positions of the EU member states on other elements of the climate package,” the campaigners said. “We give the EU 8 out of 10 for its renewables deal.”

Frauke Thies, Greenpeace’s renewables expert, voiced reservations only about the biofuels factor.

Claude Turmes, the Luxembourg Green MEP who led the negotiations for the European Parliament, said he had “mixed feelings” about the biofuels factor.

“Despite mounting scientific evidence on the dangers of biofuels, we were unable to completely revise this wrongheaded target… renewable energy will be put at the very heart of EU energy policies.”

The European Wind Energy Association, a lobby group, said today’s deal put Europe in the lead of “the energy revolution the world needs”. It calculated that, if the law is properly implemented, more than a third of Europe’s electricity will be generated from renewable sources by 2020.