Studies show that what’s coming is ominous. By mid-century, the four to six weeks of extremely hot weather recorded in the San Fernando Valley each year might double, said Alex Hall, director of UCLA’s Center for Climate Science. Temperatures across Los Angeles County might rise 5 percent in that timespan. In some agricultural counties in California, the heat might become too fierce for crops to grow and laborers to work.

“If we don’t take action very soon, we’re going to have to live with the consequences for a long time,” Hall said. “It’s going to be our children and grandchildren who have to cope with the decisions we are making right now.”