Angela Merkel’s Chancellery in Berlin is said to run entirely on renewable energy. That is more than can be said for 10 Downing Street, or for Germany and Britain as a whole. They will have to do a great deal better over the next 13 years to have a prayer of meeting what No 10’s current occupant called, with some understatement, the “ground-breaking, bold, ambitious” energy and emissions targets agreed yesterday in Brussels.

By 2020 carbon emissions from the world’s largest trading bloc are to be cut by a fifth, compared with 1990 levels. The proportion of the EU’s power generated from renewable sources is to rise to a fifth, and biomass must account for 10 per cent of all transport fuel. These are grand goals to declare; Herculean to accomplish. Mrs Merkel’s achievement in forging an EU climate change agreement should not be underestimated. She has, after all, persuaded Austria, which produces nearly 60 per cent of its electricity from renewable sources, and Estonia (1.1 per cent) to sign the same document. But she did so by effectively allowing nuclear power to be categorised as “noncarbon”, and by assuring the union’s poorer eastern members that they would shoulder a lighter burden than richer western countries. The arm-twisting on “differentiated national overall targets” starts now. But this much is already clear: big economies still heavily dependent on fossil fuels — like the UK — will have to change most.

Renewable energy companies have hailed yesterday’s deal almost as enthusiastically as did Mr Blair. In fact, its clearest winners are nuclear energy and the countries that depend on it most heavily, namely France and Finland.

Nuclear power is not renewable (global uranium supplies are finite) nor noncarbon (uranium mining is a carbon-intensive industry), but it is vastly cleaner than oil, gas or coal. It is, therefore, right that nuclear capacity be taken into account in setting national renewable energy targets, however much this may look like a victory for special pleading by President Chirac. And Mr Blair will be right to reiterate his belief in an expanded role for nuclear energy in Britain when the climate change White Paper is published next week.

How to set different national emissions targets depending on “different national starting points” is much less clear. Western Europe may have broken the historic link between growth and energy consumption, but the EU’s newest members have not. Poland, Hungary and the Czech Republic remain heavily dependent on coal and gas for power, and on carbon-intensive manufacturing for growth. If they are to leapfrog the energy extravagance that built the most advanced economies, it will only be with significant subsidies in the form of low-carbon technology or cross-border power supplies. Whether “rich” Europe will pay this price remains to be seen.

The EU summit did not discuss the science of climate change, but the scientific debate, rightly, goes on. Serious questions remain about why temperatures fell as carbon emissions rose after the war, and whether changes in carbon levels precede or follow temperature fluctuations over the long term. Scientists who raise these questions should not be demonised. Flaws in climate change models, if not explained, will only embolden emerging economies to abandon the greenhouse gas consensus and use relatively cheap, convenient fossil fuels to power the development that their impoverished billions desperately need. Finding true consensus on climate change within Europe will be hard. In the looming energy showdown with China, India, Africa and Brazil, it will be far harder.