San Francisco’s fog is a notorious shapeshifter. Its thick gray mists have delayed planes, derailed sporting events, and even obscured the grand opening of The City’s tallest tower.
Our distinctive marine layer, known as both Karl and Karla on social media, has been the subject of books and documentaries and even starred as the main ingredient in locally distilled fog-harvested martinis.
But as the climate warms, mounting scientific evidence suggests that our beloved — and oft bemoaned — coastal fog is on the decline.
“I feel like, this year, there has been less of it,” said Engel Ching, a photographer and self-proclaimed “fogaholic” well known for capturing our famous fog unfurling over the Golden Gate.
Now, a growing body of research is beginning to back up Ching’s hunch. Todd Dawson, a professor of integrative biology at UC Berkeley looked at historical fog records from coastal stations and airports dating back to the 1950s and found a 33% reduction in fog frequency since the early 20th century.
“We’re really perturbing the climate system,” said Dawson. “We’re changing the way air circulates. That means that changes the way our storms behave, the severity of the storms and other things like fog formation and duration.”
Dawson found that, in general, fog seasons are starting later and ending earlier, and the number of foggy hours per day is also dipping dramatically. “We’ve lost basically three hours per day of fog,” he said.
Fog loss isn’t just an identity crisis for San Franciscans, however. It’s also an ecological problem.
Often called nature’s air conditioner, coastal fog plays a critical role in regulating temperatures and supporting Northern California’s hydrologic system, drenching old-growth redwoods in summertime moisture, recharging streams that support coho salmon and acting as a critical water supply and temperature regulator for forests, vineyards and agriculture.
“Fog is not just something that makes you put your sweater on during the summertime,” said Dawson. “It is truly an additional water subsidy to California’s (mostly) coastal ecosystem.”
California’s coastal fog forms when warm, moist air moves over the cold upwelling of the Pacific Ocean and hits what is called a dew point, or the temperature to which air must be cooled to become saturated with water vapor. But as the ocean warms, there is less opportunity for fog formation.
But not everyone is convinced that climate change is to blame for our coastal fog’s retreat. “Fog is an incredibly complicated phenomena,” said Alicia Torregrosa, program officer at the U.S. Geological Survey and member of the Pacific Fog Project, a multidisciplinary brain trust of scientists, researchers and experts. “What happens under increased solar radiation trapping of heat…is still a very open question,” she said.
Torregrosa said additional research is needed to provide definitive answers on the changing behavior of coastal fog, which even under normal conditions is challenging for weather forecasters to predict. “The more we know, the more we don’t know,” she said.
Daniel Fernandez, a professor at California State University, Monterey Bay who braves misty days to catch fog in nets for research and water collection, also has noticed a downward trend in fog accumulation along California’s craggy coastline — although he noted that fog cycles can vary dramatically from year to year.
“The modelers are not completely convinced that it will increase or decrease,” said Fernandez. “The jury’s out.” But, he said, “if anything, it’s probably shrinking.”
Fernandez and his colleagues had a nickname for the month of August: They called it “Fogust.” And although the past couple of years have certainly been foggier, “The several before that, there were very few fog events — way fewer,” he said.
Although this poses obvious challenges for his research, Fernandez stressed that there are bigger more fundamental reasons to care about fog. “It probably has something to do with why we’re here, the mixing and all those kinds of things that happen in the chemical or biological soup,” he said. “It’s its own universe in a sense.”
And while Dawson is skeptical that San Francisco will ever mirror Los Angeles, “I think we are heading for a more arid Bay Area,” he said.