Enlarge image
Only real with fog: Golden Gate Bridge and San Francisco skyline
Photo: Robert Galbraith/ REUTERS
"The coldest winter I've ever experienced was the summer in San Francisco," Mark Twain once said - at least this quote is attributed to him.
The east coast of the USA, especially the Bay Area around San Francisco, knows the weather phenomenon that a drizzle blanket of fog covers the city, worse than in Hamburg.
May Gray transitions to June Gloom, then No-Sky July, and finally Fogust.
The search for a corresponding bad weather description for September continues.
It feels like there are more pictures of the Golden Gate Bridge with fog than without.
The bridge is equipped with five fog horns.
The fog also has a cooling effect on the metropolis, in the summer months of June to August San Francisco has an average temperature of just 21 degrees, making it the coolest major city in the USA (outside Alaska).
"Mother Nature's Air Conditioning" means that less than half of local residents have air conditioning at all.
You just don't need one.
Someone even gave the nebula the nickname »Karl«.
The Twitter account "Karl the Fog" has more than 350,000 followers.
But the iconic fog could soon be over.
This is probably due to the climate crisis.
A third less fog in the past 50 years
As early as 2010, a study by the University of Berkeley came to the conclusion that the number of fog hours has decreased by a third compared to the middle of the 20th century.
Todd Dawson, a professor at the University of Berkeley, has been researching the effects of the fog on California's ecosystems for decades.
As early as the late 1990s, he had studied the redwoods in the Californian coastal region and found out that the trees, which can be up to a hundred meters high, get 30 to 40 percent of their liquid requirements from fog: the high treetops of the redwoods are, so to speak, huge filters for the wafts of mist.
The trees are watered and supplied with nutrients;
the water drips onto the forest floor.
There it supplies other plants and feeds streams - and benefits a wide variety of animal and plant species such as lichens, ferns, newts and salmon.
more on the subject
Get moisture out of the air: With mist catchers against drought
People all over the world have copied this process from nature.
Spain and Portugal are currently testing methods of removing moisture from the air using special collectors.
This process is also used in Nepal and Peru and could even help mitigate the effects of climate change there.
The only problem in California is that there is less and less fog that could be caught.
Less fog also in Los Angeles and São Paulo
And that applies worldwide, as the climatologists Otto Klemm from the University of Münster and Neng-Huei Lin from the Tawian National Central University found out in a 2015 study.
The scientists are documenting a reduction in fog everywhere in the world: in São Paulo, the number of foggy days has halved from over 144 per year in the early 1950s to a good 70.
In Los Angeles, the number has even decreased from 200 to 30 in the same period.
The reasons for the fog disappearance are unclear.
Both climate change and reduced air pollution could be the cause.
Probably even both together.
"Less fog is a game changer for a lot of things," Dawson told the New York Times.
He says he's seeing the effects of the dwindling fog on the redwoods.
"Growth is stunted on some older trees," he said.
"They're not growing as fast as they used to, and their treetops are thinning," he told Inside Climate News in 2021.
He fears that at some point the sequoias will no longer be able to sustain themselves.
"They just won't make it anymore." When that will happen, however, he cannot say.
Fog formation does not depend on just one factor, but occurs in the interplay of various influences: "Land surface, ocean surface, how strong the warming is, what the winds do, how quickly the land warms up compared to the ocean, whether the cold water buoyancy is strong or weak .«
But Dawson has made his own experiences: “I've been working with redwoods for 25 years and during that time I've seen what's happening.
I'm concerned about the future."
mgo