What climate change could mean for fog in the Bay Area
SAN FRANCISCO — It was the first morning of summer, the start of fog season. But the sky above the Golden Gate Bridge remained clear and blue.
Chris Dzierman, a bridge painter and foreperson, looked to the west. Near the horizon, where water usually meets sky, a thick fog bank lurked. He wondered if and when it would roll in, as fog usually does on summer afternoons, smothering the bridge and beyond in wind and whiteness.
“It could last three minutes or three hours,” Dzierman said. “It’s fog. It’s got a mind of its own.”
Every summer, fog breathes life into the Bay Area. But people who pay attention to its finer points, from scientists to sailors, city residents to real estate agents, gardeners to bridge painters, debate whether there is less fog than there used to be, as science and general sentiment suggest.
The ecological, economic and social effects of fog are profound, perhaps no more so than in Northern California. Changes would be life-altering. But understanding fog is one of science’s toughest tricks. Quantifying the changes and determining possible causes, including global warming, is climatology’s version of chasing ghosts.
That day on the bridge, computer models predicted the fog would push through the Golden Gate in an hour or two. Dzierman trusts his gut. He had a hunch it would stay away, defying the familiar summertime cycle.
Just then, a slight breeze, an invisible puff of chill, the kind you might get by opening the freezer door.
“Feel that?” he said, inhaling deeply. “Mother Nature’s air conditioning. Yeah, that feels good.”
It was a tease.
The day remained gloriously sunny, unusually hot and fog-free, the kind of San Francisco summer’s day that some fear is becoming more frequent. The bridge’s five foghorns went unused, for now.
While coastal fog isn’t unique to California, few places in the world are so deeply associated with the ethereal movements and cooling spritz of fog’s peek-a-boo routine. Fog pours through the Golden Gate and crawls up and down the wrinkled hills of the city and the nearby coast. It cloaks and chills. Millions are affected by it, if only by the invisible cool breezes that presage the fog’s arrival.
Fog is why one neighborhood is notoriously chilly, another is surprisingly sunny and the airport is where it is. It is why real estate agents talk about neighborhood fog patterns as much as square footage and schools. It is why fewer than half of Bay Area residents have air conditioning, and partly why they use less water than most Americans.
Summer fog is why the mighty coastal redwoods grow where they do, surviving California’s dry season thanks to refreshing gulps of cold, wet air. It is why, until recently, few people worried about wildfires along the coast.
In June, July and August, as most of the Northern Hemisphere, and most of California, feels the full force of summer heat, the average daily high in San Francisco is below 70 degrees Fahrenheit (about 21 Celsius), coolest of any major city in the continental United States.
Fog is a companion, part of the rhythm of summertime, flitting in and out of lives like a family member. But it does more than astonish ill-prepared tourists and dazzle photographers and poets. It nourishes the natural world. It enriches the area’s cultural identity. It might even be an untapped resource in California’s growing anxiety over water.
Which is why a decrease in California’s coastal fog, or the prospect of it disappearing entirely one day, is not a sunny proposition, particularly in and around San Francisco Bay.
The general consensus among the small cadre of scientists who study coastal fog is that it is decreasing, not just in California, but around the world. However, the reasons aren’t clear.
Fog may be the most difficult meteorological phenomenon to capture, calculate and predict. Unlike temperature, precipitation, humidity or wind, there is no reliable gauge for it. There is not even a practical definition of it.
Most will say that fog is a cloud that touches the ground, which sounds simple enough. But fog is movement in three dimensions, dipping and rising, forming and disappearing.
Sometimes a thin layer hugs the water below the Golden Gate Bridge, blinding mariners. Sometimes it settles about 200 feet higher, blinding drivers. Sometimes it shrouds the top of the bridge’s towers and the airspace above, blinding pilots. Sometimes it does it all. Which of those things is fog?
It arrives like a whisper and disappears like a magic trick. It is there one moment and gone the next.
Can you catch the fog?
Early on a late spring morning, Peter Weiss, a scientist at the University of California, Santa Cruz, and three of his students, calling themselves “the fog squad,” were erecting fog catchers.
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