Fog in California - it's declining

James A. Johnstone and Tod Dawson's recent paper in PNAS show that California's coastal fog has decreased significantly over the past 100 years, potentially endangering coast redwood trees dependent on cool, humid summers. Coast redwoods, Sequoia sempervirens, grow in a narrow coastal band, from Big Sur to Oregon, characterized by cool summer temperatures and high humidity from fog (see map at right from USGS).  They analyzed 20th century climate station records, and have shown that since 1901, the average number of hours of fog along the coast in summer has dropped from 56 percent to 42 percent, which is a loss of about three hours per day. Excerpted here.