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With Climate Change, What Will Happen to the Bay Area’s Fog?

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Aerial view of the California coast. On the left side of the image, the ocean laps against the shore, on the right side, plant covered sand dunes rise from the beach. Fog rolls in.
 (Carly Severn/KQED)

Read a transcript of this episode.

Any San Franciscan knows the complex relationship between the city and its pervasive companion — fog.

“I both love and get frustrated by the fog,” said long-time resident and Bay Curious listener Lily Drexler. “I appreciate how it freshens the air and changes things up. But when there is fog for weeks on end with no break, that does get frustrating.”

Drexler is getting ready to put down roots in San Francisco and is starting to look at real estate options in different neighborhoods around the city. But before she does so, she has one big question: what’s going to happen to fog in the future?

“Is it going to get more foggy as the sun bakes the ocean and creates the moisture, if that’s how fog works? Or is the heat and the warming of the planet going to decrease the fog?”

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Where should a fog-averse city dweller choose to settle down? And, more broadly, what would a future look like with less fog? How do we rely on fog now in the Bay Area and how might its absence change us?

As it turns out, the answer to Drexler’s question is not simple or straightforward. There’s a shroud of mystery surrounding fog — much like the phenomenon itself — that has scientists unsure of what the future may hold.


‘A Special Thing to Study’

Even the basic definition of fog is not widely agreed upon.

“There’s a few ways to define fog and they’re somewhat overlapping, which kind of illustrates the complication when trying to define something like fog,” said Daniel Fernandez, an environmental studies professor at CSU Monterey Bay.

According to Fernandez, in order to be considered “fog,” this weather phenomenon must have three things:

  • Air must consist of tiny water droplets between one and 50 microns — thinner than a piece of hair.
  • There must be enough of those tiny droplets that it impede our ability to see beyond a kilometer.
  • Fog is a cloud that is in contact with the ground.

In order for that cocktail of ingredients to come together, there must be a temperature gradient over a given area. The cool ocean air and hot Central Valley, for example, is conducive to fog formation. (Bay Curious explained this phenomenon in detail in our episode: Why San Francisco Gets So Windy and Foggy in the Summer)

“I find fog mysterious, fascinating, scary and exciting,” Fernandez said. “I think that’s part of what makes it such a special thing to study.”

Fernandez has been studying fog for over a decade. It started with him wondering whether he could catch fog — as in, pull it out of the air and collect it as a liquid. It turns out you can. He now has dozens of fog collectors deployed all over the state.

A man stands in a field examining a tall black mesh screen that has been mounted onto a frame .
Professor Daniel Fernandez examines one of his ‘fog collecting’ screens. On a very foggy day, one of these screens can trap up to 9 gallons of water vapor. (Dana Cronin/KQED)

They’re essentially big, 4-by-10-foot pieces of mesh reaching into the sky with troughs underneath. The water vapor collects on the mesh and trickles down. The trough feeds into a bucket that contains a data logger, so Fernandez can keep track of how much water each one has collected — as much as nine gallons of water in one day, he said.

While that’s not nearly enough to offset California’s water shortage during drought years, that water could help farmers with irrigation or assist with state reforestation efforts, Fernandez said.

The fog collectors haven’t been established long enough for Fernandez to determine whether there’s been an increase or decrease in fog over time. And given the complex set of conditions surrounding it, fog is a difficult thing to predict. It can’t be forecasted in the same way that rain can be. And that’s why there’s some disagreement in the fog science community over how climate change is impacting fog.

But, Fernandez said, there is a small cadre of scientists who believe that fog is on the decline.

“On the whole, I think that we’re going to probably be seeing less fog, in general, and that we are currently seeing less than we may have seen a generation ago,” he said.

Some studies have shown that, since the 1950s, fog has declined about 30% during the summertime.

Fernandez emphasized there’s still a lot of uncertainty in the fog science community. For example, that 30% decline could come from the fact that a lot of cities have cleaned up their air since the 1950s, so these tiny droplets of water vapor have fewer particulates to cling to. In other words, perhaps there’s less of it not because of climate change but because of improving air quality standards.

Other studies completely contradict that. At least one used observational notes from ships off the coast of California to suggest fog is getting heavier.

But, according to Dan, there’s some level of consensus that fog is on the decline. And, if true, there would be consequences here in northern California.

What Less Fog Would Mean for Northern California

We rely on fog in all kinds of ways, both big and small. One big way is to help us grow food.

A half mile from the ocean in Watsonville, Rod Koda grows strawberries on 15 acres of land. His farm, Shinta Kawahara Company, thrives on fog.

“Here along the coast with the fog, the temperatures are cooler, so the berries ripen slower and get more sugar content,” he said on a recent foggy day.

In warmer parts of California where strawberries are grown, like Salinas and Gilroy, strawberries ripen more quickly. One heat wave and the berries have to be picked immediately. Whereas, thanks to the fog, Koda has more flexibility.

Fog even helps with simple tasks, like laying down plastic in preparation for planting strawberries, which Koda’s crew is working on the day I visit.

“It comes out really nice because the dirt is a little softer,” Koda said.

A man wearing a denim shirt and dusty jeans smiles warmly at the camera while standing in a plowed dirt agricultural field. A green tractor can be seen in the background.
Rod Koda, owner of the Shinta Kawahara Company, grows strawberries in Watsonville, CA. He says fog helps his berries grow slower and sweeter. (Dana Cronin/KQED)

In addition to temperature, strawberries also rely on the moisture from fog.

“Strawberry crops have greater water use efficiency during fog events compared to non-foggy periods,” said Sara Baguskas, an environmental professor at San Francisco State University.

Baguskas conducted research in Salinas Valley to find out how strawberry plants interact with fog. Ultimately, she found that strawberries don’t need as much water when it’s foggy and that they use sunlight more efficiently on foggy days.

“Even though the total amount of light that’s used by plants is lower like it’s dimmer, the photons are scattered, and so more of the leaves are engaged in photosynthesis in the plant,” Baguskas said.

Koda has noticed that on his farm.

“We typically have fog in July and August, and usually our volume is up during those times,” he said.

He hasn’t really noticed any major changes in the fog patterns in the decades he’s been farming. Every year feels different, he said.

But in a future without fog, farmers like Koda would have to compensate. In the future, growing strawberries could require more water, and some farmers might not have the same flexibility they have now when it comes to harvesting. And, for us consumers, the berries might be less tasty and more expensive.

And there are other ways the disappearance of fog would fundamentally change the Bay Area.

Redwood trees, for example, are natural fog catchers. They essentially drink it in, relying on it for survival. It’s why they’re unique here to Northern California.

Many other species rely on fog, too, including manzanita trees and even certain types of lizards. That can have a ripple effect throughout an ecosystem.

“Because when one element of an ecosystem is impacted, how does that affect others?” said fog scientist Dan Fernandez.

Fog may even protect us from wildfires to some extent. The moisture it provides acts as a fire retardant and without it, Fernandez said many more areas would be susceptible to megafires.

Without fog, life in the Bay Area will change.

Two people stand silhouetted on a cement walkway while the Golden Gate Bridge is just barely visible through thick fog in the background.

The Real Estate of it All

In short, there’s no straightforward answer to Bay Curious listener Lily Drexler’s question about fog and climate change.

But here’s some straightforward advice about what to look for in real estate: buy in a neighborhood that you can see yourself living in now.

“If it’s of concern to people, I would literally counsel them and say this house is going to be in the fog. If it’s a problem, then we probably need to look elsewhere,” said Alexander Clark, owner of Front Steps Real Estate in San Francisco, who has written about this topic before.

Clark said while he’s no fog scientist and doesn’t know what will happen in the future, his advice for a fog-averse house hunter is to focus your search on sunny neighborhoods. Though, he warns, those tend to be pricier.

Whether or not you want to live in the fog is a critical consideration, he said. “It’s a pretty important thing for people to know because it definitely affects people.”

Episode Transcript

This is a computer-generated transcript. While our team has reviewed it, there may be errors.

Olivia Allen-Price: Lily Drexler grew up in San Francisco. And as anyone who lives in San Francisco can relate to… she has a complicated relationship with fog.

Lily Drexler: I both love and get frustrated by the fog. 

Olivia Allen-Price: On the one hand…

Lily Drexler: I appreciate how it freshens the air. I appreciate how it changes things up. 

Olivia Allen-Price: But, it can get old.

Lily Drexler: When there is fog for, you know, a week, weeks on end with no break, that does get frustrating.

Olivia Allen-Price: I feel you, Lily. Lily rents in the Richmond district right now… and she’s thinking of settling down in San Francisco more permanently, maybe even investing in some real estate. But before she does that, she has some questions about fog. 

Lily Drexler: Is it going to get more foggy as the sun bakes the ocean and creates the moisture, if that’s how fog works? Or is it going to get less? Is the heat and the warming of the planet going to decrease the fog?

Olivia Allen-Price: As climate change alters everything in our region … where does that leave fog? 

Where should a fog-averse city dweller settle down? We’re going to answer that question … but we’re also going to zoom out and look at fog’s future in the Bay Area at large. How do we rely on fog now…and how might its absence change us? I’m Olivia Allen Price and you’re listening to Bay Curious.

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Olivia Allen-Price: What does the future of the Bay Area’s fog look like, Lily Drexler asked Bay Curious…  We sent reporter Dana Cronin out to get some insight…

Curious music

Dana Cronin: It’s a foggy day in Monterey. At least, I thought it was.

Dan Fernandez: The fog literally has to be at ground level. So I would call this low cloud, which might become fog. 

Dana Cronin: This is fog expert Dan Fernandez. He’s a professor at CSU Monterey Bay. As you can tell… I have a lot to learn about fog before I try to answer Lily’s questions. And Dan’s gonna help me. 

Dana Cronin: He’s been studying fog for more than a decade. Before he studied it, he was an electrical engineer and worked on measuring ocean surface currents. He thought about fog from time to time. But his real fascination with it came to him during a meditation retreat. He says he was sitting there meditating. It was a hot day. And he was thirsty. 

Dan Fernandez: And of course when you’re meditating, minds go all sorts of places and this is where my mind went, went into water and then fog. 

Dana Cronin: More specifically, he wondered whether he could catch fog… as in pull it out of the air and collect it as a liquid. Turns out… you can.

Dan Fernandez: So this is one of ten of the larger fog collectors that I and a class of mine deployed here back in spring 2018. 

Dana Cronin: We’re standing next to a fog collector. It’s basically a big, 4-by-10 piece of mesh reaching into the sky with a trough underneath. 

Dan Fernandez: So fog hits here on all of them, drips down, runs down this trough. And you can see birds visited, too. Even though I have bird spikes there, the water runs into the rain gauge. It goes through the rain gauge. It’s recorded here. And I have a data logger in there that records all the volume of water going through.

Dana Cronin: Because it’s apparently not a foggy day today… there’s no water in the buckets. But when it’s SUPER foggy, Dan says he’s collected as much as nine gallons in one day. 

Dana Cronin: You might wonder what the point is of catching this fog. Could it be enough to help offset California’s water shortage during drought years, for example?

Dan Fernandez: There’s certainly not enough for us to consume the amount of water we consume.

Dana Cronin: So, no. But, Dan says, it could help farmers with irrigation. Or provide water for reforestation… which Dan’s fog collectors are working on now. He hasn’t had them set up for long enough to figure out whether there’s been more or less fog over time. And he says that question… how climate change is impacting fog… isn’t that simple. 

Dana Cronin: There’s no general consensus in the science community about what will happen to fog in the future. In fact, they can hardly agree on how to define it. 

Dan Fernandez: There’s a few ways to define fog and there’s somewhat overlapping, which kind of illustrates the sort of the complication when trying to define something like fog.

Dana Cronin: According to Dan, for something to be considered “fog,” it needs to have three things. One:

Dan Fernandez: So fog consists of water, tiny little droplets that vary in size between one-micron diameter spheres and 50-micron diameter spheres. 

Dana Cronin: Your hair is about 100 microns. So these water droplets are thinner than that… so thin that they float in the air. 

Dan Fernandez: But there have to be enough of these droplets to impede our visibility to be less than one kilometer. Then it’s defined as fog. 

Dana Cronin: If you can see beyond one kilometer, then it’s considered mist — NOT fog. And thirdly…

Dan Fernandez: Fog is a cloud that’s in contact with the ground. 

Dana Cronin: So, fog has to hover near the ground, it has to limit our visibility to one kilometer… and it consists of droplets between one and 50 microns. Simple, right?

Dana Cronin: And for that cocktail of ingredients to come together and form fog… we need a temperature gradient, as in something warm and something cool, like the cool ocean and the hot Central Valley, for example. As cool ocean air reaches land and warms up, it condenses and forms fog. It’s a complex phenomenon! But that’s why Dan likes it.

Dan Fernandez: I find fog mysterious, fascinating, it can be scary and exciting. It’s all of those. I think that’s part of what makes it such a special thing to study.

Dana Cronin: But it also makes it a difficult thing to study… and to predict. You can’t forecast it the same way you can forecast rain and thunderstorms. And that’s why scientists don’t know exactly how climate change is impacting fog. But Dan says they have an idea… 

Dan Fernandez: You know, on the whole, I think that we’re going to probably be seeing less fog in general and that we have that we are currently seeing less than we may have seen a generation ago.

Dana Cronin: Some studies have shown that since the 1950’s fog has declined about 30% during the summertime. But Dan says there’s still a lot of uncertainty in the fog science community. For example… that decline could come from the fact that a lot of cities have cleaned up their air since the 50s… so fog has fewer particulates to cling to. Meaning, perhaps there’s less of it not because of climate change — but because of changing air quality standards. 

Dana Cronin: And some studies completely contradict that… at least one used observational notes from ships off the coast of California to suggest fog is getting heavier. 

Dana Cronin: But, according to Dan, there’s some level of consensus that fog is on the decline. And if that’s true… there would be consequences here in northern California. Because, as it turns out, we rely on fog in all kinds of ways — both big and small. I’m gonna walk you through a few of them. Starting with something we’re known for. Our food. 

Dana Cronin (in tape): It is a very foggy day on the farm here. Wow. 

Dana Cronin: No, for real this time. I’m at Shinta Kawahara Company farm in Watsonville, about a half mile from the ocean. I’m meeting up with farm owner Rod Koda.

Dana Cronin (in tape): Can you usually see the ocean from here? 

Rod Koda: Yes. We’re in the Monterey Bay. Um, on a nice day, I could see Pacific Grove and all the way to Santa Cruz. But not today. We got fog. It’s nice. Perfect. 

Dana Cronin: Rod grows strawberries. Today his crew is preparing for planting… using a tractor to lay down plastic to protect the strawberries. 

Tractor sounds

Dana Cronin: Rod says the fog is actually helping this process.

Rod Koda: It comes out really nice because it’s last that the dirt is a little softer. 

Dana Cronin: And it helps in other ways too. Rod says in other parts of California where strawberries are grown… like Salinas and Gilroy… it’s warmer, and the berries ripen more quickly. One heat wave and the berries have to be picked immediately. Whereas, thanks to the fog, Rod has more flexibility.

Rod Koda: Here along the coast with the fog. The temperatures are cooler, which the berries ripen slower and get more sugar content.

Dana Cronin (in tape): So you’re saying they’re better strawberries along the coast with the fog influence or, well, tastier. 

Rod Koda: Exactly

Dana Cronin: In addition to temperature… strawberries also rely on the moisture from fog… says environmental professor Sara Baguskas.

Sara Baguskas: We learned that strawberry crops have greater water use efficiency during fog events compared to non-foggy periods.

Dana Cronin: That basically means that strawberries don’t need as much water when it’s foggy. Sara’s team also found that the strawberry plants use sunlight more efficiently when it’s foggy. 

Sara Baguskas: Even though the total amount of light that’s used by plants is lower, it’s like dimmer, but the photons are scattered and so more of the leaves are engaged in photosynthesis in the plant. 

Dana Cronin: So basically, when it’s foggy, strawberry plants are more productive and need less water. Rod has noticed that on his farm. 

Rod Koda: We typically have fog in July and August. And usually our volume is up during those times.

Dana Cronin: He says he hasn’t really noticed any major changes in the fog patterns in the decades he’s been farming. Every year feels different, he says. But if what fog scientist Dan Fernandez said is true, and there won’t be as much of it in the future, farmers like Rod might have to compensate. In the future, growing strawberries could require more water… and farmers might not have as much flexibility around when they harvest as they do now. And for us consumers… the berries might be less tasty and more expensive. 

Music

Dana Cronin: Besides strawberries… there are many other ways the disappearance of fog could impact the Bay Area. So many of our ecosystems here rely on it —todd both for moisture and for the cooler temperatures. Redwood trees, for example, are natural fog catchers… they basically drink it and need it to survive. It’s why they’re unique here to Northern California.

Dana Cronin: Fog scientist Dan Fernandez says there are many other species that rely on it, too… including manzanita trees and even some types of lizards. 

Dan Fernandez: And so when one element of an ecosystem is impacted, how does that affect others?

Dana Cronin: Fog may even protect us to some extent from wildfires. The moisture it provides acts as a fire retardant… and without it, Dan says many more areas would be susceptible to megafires. Overall… the loss of fog would fundamentally change the Bay Area. 

Music ends

Olivia Allen-Price: OK Dana, but there’s one part of Lily’s question that’s still missing… where should she invest in property?

Dana Cronin: Well… like I said in the story, fog is really hard to predict. There isn’t a neighborhood-by-neighborhood projection of what its future looks like in San Francisco. But… I did reach out to a real estate agent to get their take on the situation. 

Alex Clark: A lot of my clients ask me like, So what’s the fog like with what are you going to do? And luckily, I know a lot about like the weather and just all the patterns and wind and which side of the street’s better…

Dana Cronin: This is Alex Clark, owner of Front Steps Real Estate in San Francisco. He told me fog is a really important thing to factor in when buying property. And while he’s no fog scientist… and doesn’t know what will happen in the future… he says the most important thing is to buy in a neighborhood that you can see yourself living in now. 

Alex Clark: If it’s of concern to people, I would literally counsel them and say this house is going to be in the fog. If it’s a problem, then we probably need to look elsewhere.

Olivia Allen-Price: Well, that’s something! Good luck in your search, Lily.

Music

Olivia Allen-Price: That story was reported by KQED’s Dana Cronin. 

Olivia Allen-Price: Next week, our December Bay Curious newsletter goes out. We ventured to a Christmas Tree Farm in Petaluma to learn about the year-round work that goes into growing the perfect tree. It’s part of our unusual jobs series in the newsletter. Be sure you’re subscribed at baycurious.org/newsletter.

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Olivia Allen-Price: Bay Curious is made in San Francisco at member-supported KQED. Our show is produced by Amanda Font, Christopher Beale, and myself. Additional support from Jen Chien, Katie Sprenger, Cesar Saldana, Maha Sanad, Holly Kernan and the whole KQED Family. I’m Olivia Allen-Price. Have a wonderful week.

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