He has a point of course: governments will seize any excuse not to confront the electorate with hard choices, and to assist a powerful and none-too-scrupulous nuclear industry. But I feel we have a duty to be as realistic as possible about how we might best prevent runaway climate breakdown.

It’s true that my position has changed. As the likely effects of climate change have become clearer, nuclear power, by comparison, has come to seem less threatening. Three things in particular changed my view:

- reading the technical report by the Finnish radioactive waste authority Posiva -  http://www.posiva.fi/raportit/POSIVA-2002-01.pdf. This seems to me to be a convincing demonstration that the long-term storage of nuclear waste could, in principle, be carried out safely.

- reading the Sustainable Development Commission’s paper on nuclear safety and security -  http://www.sd-commission.org.uk/publications/downloads/Nuclear-paper6-SafetyandSecurity.pdf . I was also struck, reading all the papers in this series -  http://www.sd-commission.org.uk/pages/is-nuclear-the-answer.html - by the gap between the evidence the SDC amassed and the conclusions it came to. The technical papers suggested that modern nuclear power production is safe, sustainable in terms of uranium supply and a source of low-carbon electricity. The SDC’s position paper, however -  http://www.sd-commission.org.uk/publications.php?id=344 - came out strongly against it. I found this hard to understand.

- discovering that routine discharges of ionising radiation from coal plants are higher than from nuclear power stations -  http://www.sciam.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste

But I have not, as many people have suggested, gone nuclear. Instead, my position is that I will no longer oppose nuclear power if four conditions are met:

1. Its total emissions - from mine to dump - are taken into account

2. We know exactly how and where the waste is to be buried

3. We know how much this will cost and who will pay

4. There is a legal guarantee that no civil nuclear materials will be diveerted for military purposes.

None of them are insuperable. In the UK Condition 4 already applies: as long as chapter 7 of the Euratom Treaty is rigorously enforced -  http://eur-lex.europa.eu/en/treaties/dat/12006A/12006A.htm
The big block is Condition 2. The most fundamental environmental principle, taught to every child before their third birthday, is that you don’t make a new mess until you have cleared up the old one. It seems astonishing to me that we could contemplate building a new generation of nuclear power stations when we still have no idea where the waste from existing nukes will be buried.

In these respects my position differs from Mark Lynas’s. He would impose fewer barriers to building new nuclear power stations -  http://www.marklynas.org/2008/9/19/why-greens-must-learn-to-love-nuclear-power.

So why contemplate nuclear power at all? Why not, as Merrick suggests, decarbonise our economy solely through energy efficiency and renewable power?

In principle it could - just about - be done, as Mark Barrett at UCL -  http://www.cbes.ucl.ac.uk/projects/energyreview/Bartlett%20Response%20to%20Energy%20Review%20-%20electricity.pdf - and the authors of the ZeroCarbonBritain report - www.zerocarbonbritain.com - suggest. But as you load more renewable energy onto the grid, it becomes more expensive and harder to manage. As Mark Barrett, ZeroCarbonBritain and the German government -  http://www.dlr.de/tt/Portaldata/41/Resources/dokumente/institut/system/projects/TRANS-CSP_Full_Report_Final.pdf - have shown, you could have a balanced, reliable electricity supply consisting largely of renewables. But the balancing costs will rise a good deal as the penetration of renewables increases beyond, say, 60 or 70%. It is also worth noting that some of the more ambitious renewables proposals will take at least as long to implement as a new nuclear programme. We could decarbonise the electricity supply quicker and more cheaply if we complement renewables with other sources.

So what should these be? My priorities are as follows:

1. Gas with carbon capture and storage (CCS).
2. Nuclear power.
3. Coal with CCS.
4. Gas without CCS.
5. Coal without CCS.

I have listed them, in other words, in terms of their impacts on both the climate and the wider environment. While gas comes top of the list, we cannot ignore the threats to its security of supply (though this could possibly be ameliorated by means of underground coal gasification).

All I am seeking to do is to be clear about the opportunities and obstacles. I realise that this will provoke hostile responses from almost everyone - including my friends - but we do our cause no favours by obscuring the choices we face.