RENEE MONTAGNE, Host:
Now, NPR's Christopher Joyce reports, scientists suspect the fog may be disappearing.
CHRISTOPHER JOYCE: Biologist James Johnstone grew up in Virginia, but when he moved to the University of California at Berkeley, he discovered what really weird weather can be.
JAMES JOHNSTONE: It can be 55 degrees and humid along the coast. If you go up a mountain slope or go inland just say a few miles, you can go to 80, 90 degrees and 20 percent humidity.
JOYCE: This soggy to toasty divide - scientists call it a gradient - is part of what causes California's coastal fog. The other part is what's going on in the ocean.
JOHNSTONE: There's a systematic connection between fog and a variety of other ocean and atmosphere factors that seem to be ultimately driven by the position of the high pressure cell that resides off the coast of California in summer.
JOYCE: That atmospheric cell, along with cold ocean upwelling and the land gradient, all conspire to make fog. And after looking at historical climate data for the region, Johnstone found that the fog is diminishing.
JOHNSTONE: When you look at the evolution of that land temperature pattern, it strongly suggests that there's been maybe a 30 percent decline in fog frequency.
JOYCE: And that worries people who care about California's redwood trees.
RUSKIN HARTLEY: These forests take up to maybe 30, 40 percent of their water requirements in a year from fog, here in what is essentially a Mediterranean climate.
JOYCE: That's Ruskin Hartley. He runs a 90-year-old organization called Save the Redwoods, which helped fund the fog research.
HARTLEY: The fog that's caught sustains a rich web of life - everything from the 300-foot-high tree to the salamanders, to the ferns and the (unintelligible) that really wouldn't be there if it wasn't for the influence of the fog. So, what happens to the fog is critical to the future of these forests.
JOYCE: Christopher Joyce, NPR News.
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