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By Sophie Wang
In movies, fog usually signals mystery, and walking into it can feel like stepping into the unknown. But in the Bay Area, fog is anything but unusual. For generations, it has followed a reliable seasonal pattern, rolling in on summer mornings and evenings.
What’s unusual now is that the rhythm is breaking. Fog is fading, and the cause is much clearer than a foggy morning commute.
Over the past century, fog in the Bay Area has fallen by 34.5%, which works out to around 3 to 4 hours fewer hours of fog per day. This decrease isn’t new; for example, in 2010, researchers reported a similar 33 percent decline across California.
In 2010, researchers said the likely cause is the significantly shrinking temperature gap between the coast and inland areas. In the summer, hot inland air rises and pulls cool, foggy air toward the land, much like a vacuum. As the temperature difference shrinks, the pull weakens, causing less fog to make it to the coast.
Other researchers point to warming waters in the Pacific Ocean. Fog usually depends on cold ocean water. When strong coastal winds push warm surface water offshore, deeper, cold water rises to replace it, a process called upwelling. Warm air passes over the cooler water until the moisture of the water condenses into fog. Weaker winds mean less cold water, warmer ocean surface, and the temperature difference between the ocean and the air to be smaller, causing less fog to be formed.
People aren’t the only ones affected by the fog. Redwoods located along the coast have been disrupted the most. During the rainless summers of California, fog usually helps these trees to survive.
According to research by UC Berkeley professor Todd Dawson, an expert on fog and redwoods, fog can provide 30 percent or more of a redwood’s annual water intake. It also reduces water loss by keeping the surrounding air moist.
Without fog, the redwood forests we know today might not survive. Trees depend on the fog to help prevent dehydration and water loss during the dry summer months. Losing them would also threaten the many species that depend on them for shelter. According to Save the Redwoods League, these forests support an estimate of more than 1,000 species. Fog also helps reduce the amount of water that plants lose through evaporation, which makes areas less vulnerable to extreme wildfires, and fires move more slowly when they come.
Currently, scientists have been combining meteorology, aerosol chemistry, oceanography, and cloud physics to understand fog patterns better. Through satellite observations, scientists are able to track how fog forms and changes over time, and some of this data is available on public websites showing the past 24 to 72 hours.
The loss of fog may seem minor in day-to-day life, but its effect could become serious within the next few decades. So the next time you walk into a cloud of fog, take a moment to appreciate it, and maybe check an hourly fog map to see where it’ll be next.
This article was written as part of the The Junior Journalist Program allows high-school students an opportunity to report on topics important to them and communicate with their peers while receiving training in journalism and learning to think critically about information. To support the program and this publication’s participation in it, make a donation.
