September 27, 2022

SAN FRANCISCO — While Americans from Seattle to Memphis to New York sweated their way through the swampy summer of 2022, here was the scene on an August afternoon at Fisherman’s Wharf, on the northern tip of San Francisco: Among a group of friends from Germany gawking at dozens of barking sea lions splayed on floating docks, one was bundled in a down jacket and another in a sweatshirt, and a third was shivering despite a red checkered scarf worn like a shawl.

“No one told us about how windy it is,” said Matthias Schilli, a Ph.D. student from Hamburg, as the temperature dipped into the 50s and a thick bank of fog began to roll in from the Golden Gate under the orange sky of a setting sun.

Nearby, Riley Carvalis, a recruiter for a construction company in Florida, dashed into a shop to buy a gray and white hoodie emblazoned with “San Francisco” across the chest — one of many stacked up in trinket shops for visitors who are caught unprepared.

Then there were Anders Westlund and Lilian Howell, college students visiting from Southern California, reveling in the notion that they could comfortably wear pants, long-sleeve shirts and chunky boots.

“A lot of people escape to the heat,” said Mr. Westlund, who studies management. “We’re escaping to the cool.”

Longtime residents of San Francisco have grown weary of explaining to out-of-town visitors that July and August can be fairly cold in the city. Some San Franciscans live in dread of hearing, again, the apocryphal Mark Twain quotation about the coldest winter of the author’s life being a summer in San Francisco.

Now, though, in a time of punishing summer heat waves, when weather maps urgently flash red across the country, the city is reassessing what was once seen as a liability: its chilly Pacific breezes and fog.

“Merry Fogust, to all who celebrate,” wrote one of the many San Franciscans who joined the anonymous Twitter personality Karl the Fog in promoting #FogAppreciationDay online.

San Francisco’s summer fog and cool breezes are created by a complex interaction between the atmosphere and ocean, a process that pumps cold water from the depths to the surface and acts as an air-conditioner, according to Patrick Brown, a Bay Area climate scientist at the Breakthrough Institute, a nonprofit organization.

The long-term effects of climate change on San Francisco’s cool summers are unclear, Mr. Brown said, but there is little evidence that the weather systems that keep the city cooler than inland areas will radically change any time soon. In other words, summers in San Francisco are likely to remain crisp and refreshing for many years to come.

“That may be part of our significant future messaging about what San Francisco is all about,” said Joe D’Alessandro, chief executive of the San Francisco tourism bureau. “We never shy away from pictures of the fog coming into San Francisco or people with jackets on — that is who we are.”

Mr. D’Alessandro says he is considering marketing the summer shivers with tourist slogans along the lines of, “Come cool down.”

A page devoted to the San Francisco weather on the city’s tourism website describes an “eternally springlike climate.” That may be a charitable description of the hold-your-hat winds and zip-up-your-puffy-jacket evenings in the city, when the dankness of the fog can make it feel colder than the official temperature readings.

“San Francisco residents save on wardrobe costs,” the tourist office says, “because the same clothes suffice year round — knits, light wools, long sleeves and pants.”

The steady, cold winds that sweep in from the ocean seem more essential to the character of San Francisco than the city’s transitory political squabbles and scandals, or its current role as a favorite punching bag of conservative pundits for its decidedly liberal politics.

Candlestick Park, where the San Francisco Giants played home games until 2000, was nationally notorious for its swirling winds and bone-chilling temperatures in the summer. The Giants gave out “Croix de Candlestick” pins, complete with snow atop the team’s logo, to the rare die-hards who dared to sit through extra-inning games at night.

San Franciscans have learned to mistrust even the most promising of sunny days. It is not a question of when the damp bank of fog will arrive to chill your bones, but whether you will be caught in it without your extra layers.

Warren Blier, a weather scientist with the Bay Area office of the National Weather Service, says the average temperature in downtown San Francisco hovers around 60 degrees in July and August. The average has increased by a little less than two degrees over the past half-century.

“There’s a hint of a slight warming over the years, but we can’t say for certain that it’s a real trend,” Mr. Blier said.

One climate change model shows the San Francisco area warming on average by 2.2 to seven degrees Fahrenheit by 2100. By contrast, Sacramento, about 90 miles inland, is projected to warm more quickly, by 2.9 to 8.6 degrees in the same period. New York, governed by an entirely different weather system, is projected to warm by 3.1 to 9.7 degrees, and Chicago 3.2 to 10.8 degrees, in that time.

The bottom line for San Francisco, according to the model, is not only that the city will stay relatively cool in the summer, but also that it may be less affected by climate change-induced temperature increases than cities further east will be.

Unlike other parts of the country, where every summer seems to come with new heat records, the very hottest summer days on record in San Francisco happened early in the last century: The high for July is 99 degrees, set on July 3, 1931. The second highest was set in 1905.

(The high for August is more recent: 98 degrees on Aug. 24, 2010.)

San Francisco residents, Mr. Blier says, can count on keeping their wardrobes, at least for the summer months.

“Maybe decades into the future, maybe it’s not a puffy jacket, it’s a decent sweater,” he said. “But we’re not saying it’s going to be a T-shirt and shorts. I can’t see anything that points in that direction.”

On the edge of San Francisco Bay, Brooke and Jamie Burnie, a couple from Ontario, Canada, were taking pictures of the Golden Gate Bridge framed by a pink-hued sunset. Their two boys put their hoods up.

“It’s colder here than home,” Jamie Burnie said.

It says something about San Francisco that even Canadians remark on the chilliness.

Yet locals know that the city’s real summer is just around the corner. September and October are, on average, the warmest months of the year in San Francisco, when the sea breezes die down, the fog makes its retreat and the average temperature reaches a balmy 70 degrees, sometimes going higher.

There have been only 15 days across the past century and a half when the temperature in downtown San Francisco was 100 degrees or hotter, according to Golden Gate Weather Services, a website that compiles weather data. All but four of those days occurred in September or October.

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