From the department of ominous ledes: "State officials reported a Sierra Nevada snowpack smaller than normal on Thursday and said California may be at the beginning of its worst drought in modern history." Uh oh.

Okay, so is this the onset of perennial drought in California or is it just year-to-year variability? There's evidence that what's going on now is somewhat flukish: One big culprit appears to be La Nina, which has been pushing winter storms further north, past California and up to Washington and Canada. But this could also be a sign of things to come. Just the other day, after all, there was that eye-popping study about how increased carbon concentrations in the atmosphere could eventually lead to 1,000-year Dust Bowls in the U.S. Southwest. If you're wondering how climate change could possibly affect the United States, drought is one of the big ones, and California is one of the more vulnerable states.

Last December, The Sacramento Bee took a look at what a warming world meant for the Sierra Nevadas, whose snowcaps supply some 60 percent of California's water, much of it during the dry summer months. Many of the state's dams were built under the assumption that the relatively cool and wet climate of the past 150 years would be the norm—but the modern period is actually a total aberration when you consider the whole millennium. It doesn't even take the sort of unprecedented warming we're now seeing to parch the Sierras; two-hundred year droughts were hitting the region during medieval times. Already, snowpack is down 10 percent from a century ago—and could shrink another 40 percent by 2050. The local ski industry is possibly doomed. The bigger question, though, is whether water managers are going to be able to adapt, especially in a state whose population is expected to hit 50 million people by mid-century.

--Bradford Plumer