I don't expect many Ecologist readers to agree with this, so am grateful to the editor for the chance to put my case.

I'm one of the "self proclaimed pro-nuclear environmentalists" criticised in Jim Green's article: 'Can PRISM solve the UK's plutonium problem?'. I spent 20 years campaigning against nuclear, then decided I'd been wrong, and said so.

I'm not sure who else would have 'proclaimed' this if I hadn't. Or maybe Green means that we're only self proclaimed as 'environmentalists'. Well, I've worked on green issues for a quarter of a century, and led two green organisations, so I think I could call myself an environmentalist if I wanted to.

It's humans I want to protect

But actually I don't. I work on climate change mainly because I want to do all I can to protect humans, and climate change is the greatest threat that we have ever faced. To misquote Orwell: all animals are important, but some (humans) are more important than others.

Nuclear power is not perfect, and certainly not cheap. But it is low-carbon, even when its full life cycle is taken into account. A Parliamentary Office of Science and Technology note shows that the carbon footprint of nuclear is the same as that of wind, and well below the carbon footprints of marine renewables, solar and biomass.

And nuclear generates large quantities of low-carbon electricity. The benefits of nuclear power are best summarised by James Hansen. Hansen has been a key figure in climate policy making for three decades. He was head of the NASA Goddard Institute for Space Studies from 1981 to 2013.

In 1988 he told a US Senate committee that ''It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here." Hansen's congressional evidence was pivotal in making world leaders address climate change and sign the UN Framework Convention on Climate Change.

In 2013 he and Pushker Kharecha, also of NASA's Goddard Institute, published a paper which calculated that the use of nuclear power rather than fossil fuels has prevented about 1.84 million deaths, from air pollution and climate change.

We can't do it without nuclear

Nuclear power is not the whole answer to the climate threat. Energy efficiency, renewables and carbon capture and storage are needed too, But nuclear is part of the answer. Environmental groups often argue that nuclear will deliver 'too little, too late'.

The new Hinkley nuclear power station will not start generating until the mid-2020s. In a best case scenario, how much UK energy (not just electricity) could be from renewables by then? The UK's target under the EU renewables directive is 15% by 2020 (which in the real world rather than the best case scenario we probably won't meet).

Let's assume that in the following five years we doubled renewables to 30% of total energy. That still leaves 70%. Petrol and diesel vehicles should be replaced by electric vehicles. Much of heating should be provided by electricity - with the rest coming from biogas.

So however well we do on energy efficiency, we'll need a lot more electricity. And it must be low-carbon. As David MacKay's excellent book Sustainable energy - without the hot air shows, without nuclear the numbers just don't add up.

PRISM

Green also describes me and others such as George Monbiot and Mark Lynas as cheerleaders for PRISM. I can't speak for George or Mark (and they are pretty effective at speaking for themselves), but in my own case I'm not a very fervent cheerleader.

My answer to the question "can PRISM solve the UK's plutonium problem?" is: I don't know, but it's worth a try. Green points out that it would be a new technology. It might not work. But it might. Will it be another nuclear white elephant, like THORP and MOx? Again, I don't know.

However, it was pretty clear even in advance that MOx would be a waste of money. I spent the years 1997-99 as adviser to the then Environment Minister Michael Meacher. We both did all we could to prevent consent being given to MOx. But we failed.

Nuclear technologies are not all doomed

I regret that, because I haven't changed my view on reprocessing. It's a waste of money, and leads to unnecessary levels of radioactive pollution - much higher than levels from nuclear power stations. But the fact that the UK wasted money on MOx and THORP does not mean that all new nuclear technologies will be "white elephants".

As Green notes, the UK has the highest stockpile of separated plutonium of any country in the world. This needs to be managed in some way. Green says that "PRISMs could theoretically provide a more cost-effective means of partially addressing plutonium problems than other proposals." So why not give them a go?

Or would he rather leave the stockpile where it is? Or put it down a deep disposal facility? Green doesn't answer this question, other than to say that we should stop producing more plutonium. That wouldn't get rid of existing plutonium. The stockpile can't just be wished away.

Molten Salt Reactors

The UK should also build a Molten Salt Reactor (MSR). This is not an untested technology: an MSR was built in the US in the 1950s, and another in the 1960s.

The research programme was closed down in the 1970s, probably because it did not produce plutonium which the US wanted for nuclear weapons. MSRs can in fact use plutonium as a fuel, so one could be used to reduce the stockpile.

They can also use spent nuclear fuel, getting more energy from it. Or they can use thorium, an abundant element. They reduce - though do not eliminate - the proliferation risk. And because they use liquid rather than solid fuel, they don't melt down.

Nuclear power is not perfect. But we don't live in a perfect world. To control climate change, we don't have time to make the best (energy efficiency and renewables) the enemy of the good (nuclear and CCS). We must use all of them.

Green dreams are not enough

Technology tribalism - my technology is better than yours, so I will oppose yours - should be abandoned. In theory, we could completely re-organise society, replace capitalism / competition with co-operation, and change behaviour so much that much less energy is needed.

But that won't happen any time soon. The green movement is good at dreaming, and dreams have their place. Prashant Vaze and I began our 2011 book Re-powering communities: small scale solutions to large scale energy problems with an outline of our dream. (Prashant doesn't support nuclear, so at least in writing the book we overcame tech tribalism.)

But dreams are not enough to control climate change. The green movement must become more practical and more pragmatic. That is not as poetic as deep green philosophy can be, but will be much more effective.

Stephen Tindale (@STindale) is a climate and energy consultant and Associate Fellow at the Centre for European Reform, as well as a former executive director at Greenpeace UK. He blogs at Climate Answers.

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