It's easy to understand the Japanese dream of a nuclear-free future. During last year's meltdown at the Fukushima Daiichi nuclear complex, tens of millions of residents on Japan's densely populated islands feared emergency evacuation and contamination of scarce land. Yet the government's new goal to phase out nuclear power over the next few decades would have serious costs, financial and to the climate.

Before the accident, Japan derived a third of its electricity from nuclear power. Now, most of the country’s 50 nuclear reactors sit idle. The results have been power shortages and skyrocketing imports of oil and natural gas. Not only have these taken a toll on Japanese business, harmed the nation’s quality of life and turned the country’s trade surplus into a deficit, they portend ominously for Japan’s carbon dioxide emissions. Nuclear power plants produce almost none.

Taking up an argument from anti-nuclear activists, the Japanese government claims that it will address these issues by investing heavily in renewable sources of electricity, such as solar, geothermal and wind power. But it admits that it has no details about the feasibility and cost of its goal to triple the amount of electricity the country gets from renewables, nor does it have a plan to limit the impact on emissions of burning lots more fossil fuels as renewables ramp up.

Fighting climate change is hard enough without wasting resources, and Japan's nuclear infrastructure and know-how can be valuable assets in that battle, as long as the country continues to retrofit its safety regime. A government report this year calculated that Japan might still be able to cut its carbon emissions by 25 percent of 1990 levels by 2030 without nuclear - though the government is now committing only to 20 percent. But that same report found that the country could cut those emissions by 33 percent if it got a fifth of its electricity from nuclear, and 39 percent if it derived a third of its load from nuclear. And then there is the importance of ensuring access to reliable, always-on power, of the sort nuclear used to provide the country.