The summer of 2099

Instead, imagine this: A Sierra Nevada with less than half of the snow it has today. Temperatures in the Central Valley that equal Death Valley’s. A Napa Valley too hot to grow quality grapes.

As unveiled by a team of researchers in the latest journal of the National Academy of Sciences, that’s the scenario predicted for California by the end of this century, unless radical steps to cut greenhouse emissions are taken on the national level.

Using two computer global-climate models, the team “downscaled” them to California size using a statistical method that is sound, other researchers in the field confirm. By all accounts, it is the most sophisticated study of its kind so far.

The debate over whether global warming is occurring is over. The only question now is: What are we going to do about it?

Fortunately, California is taking the lead in combating the trend. The state has already passed a law to curb carbon dioxide emissions from cars by 2009, is working to pass one limiting the amount of idling commercial diesel trucks can do, and has filed suits against the nation’s largest greenhouse emitters, coal-burning power plants in other states.

It’s not enough, however. As the report notes, even with some strong new controls, the number of over-90-degree days could double. And, lacking a serious commitment on the national level, there’s only so much California can do by itself. Voters should remember that in the run-up to the presidential election.