I took part in an online debate on nuclear energy with The Economist. Below are my opening remarks to the debate for the motion This house believes that the world would be better off without nuclear power, published on 6 April 2011. To see the full debate and online vote, visit The Economist website.

Avoiding the radiological risks associated with civil nuclear power, whether in normal operation or from a catastrophe, is not the main reason the world would be better off without it. Atoms cannot be made to work for peace without making them available for war.

This is a lesson we have learned the hard way. The original five nuclear-weapons states are now nine and will soon be joined by a tenth. All the newcomers have acquired their weapons under the guise of developing civil nuclear-power programmes.

The Nuclear Non-Proliferation Treaty has only slowed, not prevented, the spread of nuclear weapons. The skills and materials used in a nuclear-power programme are indistinguishable from those needed to build nuclear weapons. A third of the nations with civil nuclear programmes have attempted to develop nuclear weapons.

There can be no argument that the world would be better off without more nuclear-armed nations. This can only be guaranteed by removing the political cover provided by civilian nuclear-power programmes. The enormity of the proliferation risk therefore demands that the case for continuing these programmes, and thus maintaining this perilous ambiguity, be overwhelming. It is not.

If there is no compelling reason to accept the proliferation risk, then the world will be better off in many other ways. Among them will be reduction of the economic risks of nuclear accidents. They are significant. The catastrophe at Fukushima is not yet over but it is already clear that the eventual cost will exceed $100 billion.

Two primary arguments are advanced for accepting the Faustian bargain offered by nuclear power. The first is that nuclear power is essential for energy security. The second is that it is necessary to avoid dangerous climate change. Climate change is without doubt the greatest threat humanity has ever faced. Ensuring energy security is one of the most urgent tasks facing any government.

If there really is no alternative, then the Faustian bargain of nuclear power will have to be managed as well as is possible. But such a force-majeure argument must be subject to the most rigorous examination before its dread conclusion is accepted.

Nuclear power currently contributes surprisingly little to energy security—about 13% of the electricity delivered globally in 2009, perhaps as little as 2% of final energy. This was rather less than the 18% delivered by co-generation and renewables. Furthermore, this share is declining. In recent years more reactors have closed than have opened.

Last year alone, not counting large dams, renewables added 50 gigawatts of new capacity—equivalent to about 40 nuclear reactors. The International Energy Agency, not known for its nuclear scepticism, projects that the number of new reactors built in coming decades will barely keep pace with the number closing.

Even that will take a heroic effort. Some 260 new reactors would have to come on line by 2025 just to stand still. This would be a significant engineering achievement and would stretch the nuclear supply chain tightly, with big implications for costs. But it is hard to see what this does for energy security and it clearly does not displace much coal or gas.

The reality is that, even in a more electricity-dependent world, the contribution of nuclear power to world energy supplies is so small that it is already being replaced by improved energy efficiency, renewables and fossil fuels. These options are cheaper, less risky and quicker than nuclear.

But they are also, at least in the case of fossil fuels, much more damaging to the climate. Nuclear is clearly a low-carbon option. Understanding what is happening in China is central to dealing with this horn of the energy-climate dilemma.

China has the most ambitious nuclear programme anywhere with more than 70 gigawatts of new capacity planned by 2020. Should it succeed, this will meet perhaps 4% of Chinese electricity demand. A quarter will come from renewables and the remaining 70% from coal and gas—mainly coal. In carbon-reduction terms, even the world’s most aggressive nuclear programme is marginal. Not even the most valiant of nuclear advocates would suggest that a significant proportion of China’s projected coal burn could be displaced by nuclear.

But if this coal burn goes ahead unabated there is no prospect of avoiding dangerous climate change. Of course, this is not just a problem for China—many other countries have large coal programmes—but rather that the message is at its clearest there.

Nuclear power cannot save the world from the necessity of deploying carbon capture and storage or facing the impossible choice of letting the lights go out or destroying climate stability. It is a high-risk distraction from what must become the central focus of the effort to deliver energy and climate security simultaneously.