The Fog of San Francisco

Those of us fortunate enough to routinely cross the Golden Gate Bridge, one of the great bridges of the world, know what to expect in the summer. Fog often whips through the suspension cables. Tourists are bundled up in new souvenir sweatshirts. It can feel like being in a localized storm. I love it.

On the bridge on a foggy day, even in the middle of a summer heat wave elsewhere in California, the thermometer in my car, measuring the cold air rushing off the Pacific, will usually read 59 degrees. As I drive home, that temperature gauge ticks up, steady as the odometer. Where I live, 20 miles north of the bridge, it could be 100 degrees — a 40-degree range in about 15 minutes.

Fog is more than just a surreal quirk of San Francisco and the surrounding Bay Area. It is a vital part of its climatology and culture. It is a life force — and one with an uncertain future.

With that in mind, I spent much of this summer chasing fog and the people who study it, live in it, even try to catch it. The result is a report for our Climate desk, filled with graphics and photos, all trying to clear the air on fog.

Fog is fickle — hard to predict, hard to research, even hard to define. It might be the trickiest thing in meteorology to measure. Unlike temperature, humidity, wind or precipitation, there is no reliable gauge for fog. We know how it forms, but we don’t know precisely where it’s going — later today, or in the years ahead.

That is what vexes scientists. We know that the world is warming at a frightening rate, but no one is quite sure what climate change is doing to fog. The general sentiment from scientists and locals is that it is disappearing. One seminal study in 2010, using observational data from coastal California airports, concluded that fog had declined by one-third since 1951.

Ramifications are huge. Coastal California’s Mediterranean-style climate gets almost no rain from mid-spring to mid-fall. The in-and-out daily rhythm of fog in the summer, the mostly reliable bursts of cool air, is the reason most of us within a quick drive to the coast do not have air-conditioning. It is the reason the world’s tallest trees, the coastal redwoods, survive through otherwise dry summers. It is the reason, from June through August, San Francisco is the coolest major city in the continental United States, maybe the last refuge of refreshing cool air in our warming summers.

All that depends on fog and the cool ocean air it ushers in.

So I went searching for fog and those who spend their lives with it. It led me to, among others, researchers who try to capture it, wringing the air of water the way that redwoods do, to see if fog can be a viable water source. They love the fog.

It took me on a Coast Guard lifeboat and to a control room for San Francisco Bay’s vessel traffic. They hate the fog.

And it took me to what might be the most famous foggy place on the planet: the Golden Gate Bridge. (The emoji for “foggy” shows a cloud and the top of a suspension-bridge tower that looks suspiciously familiar.) Bridge employees include those with the never-ending task of painting the bridge — fog or shine — and those who control something that tourists do not see, but certainly hear: the foghorns.

Now, driving across the bridge, I can point out to my family where those foghorns are. And we will continue to play our usual guessing game as we approach the bridge: Will there be fog? Will we see the tops of the towers?

That’s the beauty of San Francisco’s fog: We never know for sure. But as I tell the kids, fog is a good thing. This place wouldn’t be what it is without it.

Fog shrouds some Bay Area neighborhoods and drenches others in sun. Here is the full story, with photographs by Nina Riggio and graphics by Scott Reinhard.

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Thanks for spending part of your morning with The Times. See you tomorrow.

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