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California is regarded as a leader in addressing climate change. But in 2012 its carbon emissions actually increased more than 10 percent, bucking the national trend of decreases. That's in large part because California closed one of its few remaining nuclear power plants. That shift in emissions underscores the huge impact nuclear power can have in efforts to combat climate change.
NPR's Richard Harris reports.
RICHARD HARRIS, BYLINE: Back in the 1980s, Armond Cohen was decidedly opposed to nuclear power.
ARMOND COHEN: I started out as a lawyer fighting a nuclear power plant in New Hampshire. Seabrook.
HARRIS: And he says authorities did the right thing when they shut down California's aging and troubled San Onofre nuclear power station near San Diego. But he's not happy to see California lose a major source of low-carbon energy. That's because these days Cohen heads a non-profit called the Clean Air Task Force and their focus is climate change.
COHEN: San Onofre produced as much carbon free energy as all the wind power installed in California to date. So you know, that's going to be a pretty heavy lift to replace all of that nuclear with low-carbon energy.
HARRIS: Cohen has becoming a grudging proponent of nuclear power, as he looks at the scale of the problem to be sold. World energy demand is likely to double or triple in the next few decades. And while wind and solar should be expanded as fast as they can, Cohen is just plain worried about how quickly they can grow from their niche status today. It's a question of scale.
COHEN: If you drive by the San Onofre site, you see two cooling towers sitting on a few acres of property. Think about that and think about tens of thousands of wind turbines that equal that same amount of energy. And then you get what I'm talking about in terms of the tradeoff and the scalability problems associated with renewable energy.
HARRIS: Cohen points to a recent study that looked at what it would take for California to reduce carbon dioxide emissions 80 percent by mid-century. It concluded that renewable sources are important, but to hit the target and have reliable power around the clock, the state would need to get one-third to two-thirds of its energy from nuclear power. Jane Long with the California Council on Science and Technology co-authored that study.
JANE LONG: I think you can do it all with renewable energy. Just how long will it take? Can you do it by 2050?
HARRIS: The study found renewables couldn't meet that deadline, but nuclear power could. That would require bringing the industry back to its once-rapid pace of construction, building a nuclear plant every year. Right now that idea isn't just unpopular, it's downright illegal in California. The state has banned new nuclear plants until there's a permanent home for the waste, so that idea is going nowhere.
And Mark Jacobson at Stanford University says that's a very good thing. He argues that the nuclear discussion is a distraction from a much better solution, an all-out effort to expand wind and solar and a few other sources of renewable energy.
MARK JACOBSEN: It's cleaner to go wind and solar. You can put it up faster. There's a larger abundance of it. There's the potential to power the entire world many times over. And the cost is coming down, whereas nuclear costs are going up.
HARRIS: Nuclear plants take a decade or two to plan and build, so Jacobson doesn't see nuclear as a speedy solution at all. And he says there are problems of scale as well.
JACOBSEN: If you wanted to power the entire world on nuclear, you would need about 17,000 large nuclear power plants, that's 850 megawatts. And we only have 400 today.
HARRIS: Jacobson authored a study that shows a path to a 100 percent renewable energy future. There are numerous studies arguing this point, one way or the other. But Jacobson has no doubt about his conclusions.
JACOBSEN: Yeah, I'm absolutely sure we can do it. It's a question of whether we want to do it and whether we will do it.
COHEN: That may be possible, but it's not something you want to bet the planet on.
HARRIS: Armond Cohen acknowledges the risk of a nuclear accident and the dangers of proliferating nuclear weapons. But he's also looking ahead to a world likely to be transformed, possibly catastrophically by global warming, over the course of this century.
COHEN: Unfortunately we're in a world of choose your poison.
HARRIS: So Cohen says there's a logic to building new improved nuclear reactors now. In fact, China has 30 advanced Westinghouse units under construction. And there's a logic to pressing forward on a new generation of reactors with more safety features.
COHEN: I can tell you it wasn't easy for me as a lawyer who back in the '80s started my career fighting nuclear power to come around to the view that it actually may be one of the things that's necessary in the portfolio to save us. But that's where the facts lead you.
HARRIS: And in the end, the biggest issue is not trying to decide how much nuclear energy needs to be in the mix. It's motivating governments to take on the enormous challenge of phasing out cheap and abundant fossil fuels and building a cleaner energy supply for the planet. Richard Harris, NPR News.