Goodbye California Coastal Fog, Goodbye Redwoods [View all]

[Panich52]

In Southern California they call it the “June Gloom” — the gray layer of heavy fog that drapes itself across much of Los Angeles in late spring. Here in the San Francisco Bay Area, we just call it “summer”: The months-long cycle of overcast mornings and chilly evenings that supposedly* prompted Mark Twain to complain that “The coldest winter I ever saw was the summer I spent in San Francisco.” While coastal California’s summer fog has long annoyed residents and tourists alike, the regular rush of cool, wet air helps sustain coastal ecosystems, including the state’s iconic redwoods. Now, thanks to human development, that weather phenomenon is at risk.

According to a story published last week in the journal Geophyiscal Research Letters, coastal fog in the Los Angeles region is on the decline. In the last 60 years, according to researchers, summer fog in the LA area has decreased by 63 percent. The culprit? The so-called “urban heat island effect” — a phenomenon in which the ambient temperature of cities is much higher (especially at night) than in surrounding undeveloped areas because of all the heat that builds up in our streetscapes of concrete and asphalt.

“We used cloud data from the last 67 years, and we can see that there have been huge declines in fog that have happened and that should continue happening,” says Park Williams, a researcher at Columbia University’s Lamont-Doherty Earth Observatory. Williams based his findings on detailed, sometimes hourly, weather readings from Southern California’s many airports, and matched that against census data on population density to chart development across the region. He and his colleagues were then able to demonstrate a link between the heat island effect and the diminishment of coastal fog. “This is a really solid process that is going on, and we have enough confidence to predict that it will continue.”

Beachgoers might be pleased by the findings. More sunny days, what’s not to like? But Williams and other scientists caution that most coastal California ecosystems — from chaparral slopes to the oak-studded prairie grasslands to the towering redwoods — have evolved to rely on water they get from coastal fog.

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