George Monbiot caused quite a stir recently when he declared that the Fukushima Daiichi disaster had confirmed him as a supporter of nuclear power as part of the solution for reducing carbon emissions. But the costs and uncertainties of the industry cast serious doubt on the prospects for a nuclear renaissance.

Monbiot is not the first climate advocate to call for more nuclear power. Steward Brand, famous as publisher of the Whole Earth Catalog, has announced that he favours building more nuclear power because, as he puts it, "coal is so awful."

Such declarations are taken as evidence that environmentalists are becoming more hardheaded about energy economics. Monbiot complains that renewable energy advocates are using a double standard in assessing the economics, but nuclear power has never been able to stand on its own without government backup.

If the costs and benefits of nuclear power are so attractive, where are the investors? At least with wind and solar power, it is possible to see the cost curve dropping to the break-even point in the near future. Nuclear power, by contrast, may never be able to convince investors to put their money down without government guarantees.

The prospect of cost overruns, waste disposal and extended shutdowns are daunting enough. But mostly, it is the potential cost of catastrophic failure that scares away investors. Large-scale disasters, however rare, are colossally expensive, as well as dangerous. The first estimate of entombing the Fukushima plant is $12bn. And this doesn't include the other liabilities that could force the Japanese government to nationalise the Tokyo Electric Power Company (Tepco).

Several years ago, I heard Jeff Immelt, the CEO of General Electric, say that commercial nuclear power won't be developed in the US without federal liability or financing guarantees. The risks, however remote, are so expensive that investors don't want to take them on, no matter what the return.

Monbiot, Brand and others rightly point to the heavy health and environmental costs of coal power. Researchers from Harvard recently published a study titled "Full cost accounting for the life cycle of coal" (pdf) that calculates the full health and environmental costs of coal power in the US to be $175bn to $523bn annually. The costs in China, with its lax or nonexistent health and environmental protections, may well be much higher. Reducing the use of coal is perhaps the single most important thing we can do to reduce air pollution and protect our climate.

The total costs of coal may be high, but the total costs of nuclear power are, in any meaningful sense, incalculable. Investors face cost overruns that could burn through even the deepest pockets. The true cost of waste disposal still is not known. The cost of decommissioning, even decades away, is also a big unknown. And the cost of catastrophic failure is more than a company as large as GE is willing to face. How can any investor calculate the return on investment with such large uncertainties?

And yet the cynics still assert that nuclear power is more practical than renewable energy. Renewable advocates are finding ways to promote solar and wind energy – without requiring the feed-in tariffs Monbiot cites as too expensive.

Looking at the bigger picture, I don't see why I or anyone should apologise for advocating developing energy resources that don't blow up and take their investors with them. The renewable energy advocates I work with are willing, and even eager, to discuss the full costs and benefits of all sources of energy. Supporters of nuclear power should be willing to hold themselves to the same standard.