Goodbye California Coastal Fog, Goodbye Redwoods

Written by Jason Mark

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.

Todd Dawson, a biologist at University of California, Berkeley, says that many coastal plants — not just trees, but also the understory of shrubs and grass — depend on the water they receive from fog drip. Coastal redwoods, for example, get up to one-third of their total annual water needs from fog. “You think that all of this water is coming from winter rainfall, and of course a lot of it does,” Dawson says. “But a lot of it also comes from fog, and that fog comes during a really important time, during the summer, the longest and warmest days of the year. The fog subsidy is really important for their ecology and their physiology.”

Williams says that it would be useful to have a better understanding of the degree to which coastal fog sustains chaparral ecosystems, and whether a decrease in fog cover could be making such areas more flammable and prone to wildfires. “I don’t think that anyone is studying whether chaparral has become more flammable in the last 30 years,” he says, “but I would hypothesize that they have.” In short: less fog could mean more intense wildfire seasons.

Williams’ current study only looked at Southern California. He says that he’s interested in extending his research into the San Francisco Bay Area, where more than 6 million people live in close proximity to some of the world’s most iconic redwood groves, such as Muir Woods National Monument. Biologist Dawson says, “The open questions is: OK, this is happening in Southern California, but what’s happening here in Northern California, where the coastal redwoods live?”

* While this quip is frequently attributed to Twain, it might be apocryphal. See here.

This post originally appeared on Earth Island Journal.

K-Cup Inventor Admits He Created an Environmental Monster
So You Use Oil? No, That Doesn’t Make You a Hypocrite
Los Angeles Kids Are Healthier Since Pollution Levels Have Dropped

Photo Credit: Paul Hamilton


Siyus Copetallus
Siyus Copetallus3 years ago

Thank you for sharing.

Elaine Bauer
Elaine Bauer4 years ago

Having enjoyed Northern and Central Cal. coastal fog for decades; now living in the far Northern Oregon coast, I have a true appreciation of the frightening climate changes, and a true fear for the life of this planet! All vestiges of "coastal fog", and all that it bestows upon the surrounding landscape, are disappearing.

Anteater Ants
Anteater Ants4 years ago

very sad

Nikki Davey
Nikki Davey4 years ago

We really are mucking-up our planet.

Kamia C.
Kamia T4 years ago

I used to love the California fogs - they enshrouded the woods in a mystery that was wonderful to enjoy. The more the area heats up, even vineyards are having to move out of the area because they're no longer doing well. So sad to see an entire state basically self-destructing its major agricultural heritage so millions of people can keep crowding in.

Natasha Salgado
Past Member 4 years ago

Everything is at risk threatened thanks to our grotesque population.

feather w.
Feather W4 years ago


Yvonne AWAY Wey
Yvonne Wey4 years ago

Thank you for sharing this information

Lorraine Andersen
Lorraine A4 years ago

thanks for the update.

Christine C.
Chandra C4 years ago