The decision by PG&E to mothball the last operating nuclear reactors in California has some people cheering—and other pounding their fists. On Significant Figures, Peter Gleick writes that the closure of Diablo Canyon Nuclear Plant “rankles those who see all non-carbon energy sources as critical in the fight against the real threat of climate change.” Yet Gleick argues that with the pitfalls of nuclear energy and the high costs of retrofitting the plant, it is appropriate to shut it down and focus on developing wind and solar capacity. Meanwhile, Greg Laden considers the risk a major earthquake poses to the plant, which was built in the vicinity of four fault lines including the San Andreas. Diablo Canyon was upgraded to withstand a 7.5 magnitude quake, and the U.S. Nuclear Regulatory Commission estimates that during a given year there is a 1 in 23,810 chance of an earthquake causing core damage to the reactors. They will continue operating until their licenses expire, in 2024 and 2025.