The sun sets over San Francisco International Airport on May 8, 2024. The Bay Area experienced record-breaking heat waves this week, marking October as one of the hottest months of the year. (Tayfun Coskun/Anadolu via Getty Images)
At San Francisco’s Ocean Beach, you normally need layers to fight back the wind and the chill. Not just a hoodie but a jacket, a hat — the whole nine yards.
But this early October week, crowds flocked to the beach like it was Florida, setting up umbrellas, lying out in bikinis and going for a swim in water that was, thankfully, still frigid.
San Francisco resident Vincent Arenas was at the beach for the second day in a row with his 3-year-old son and wife to escape their sunny, warm apartment. “We really gotta get out,” he said.
Camryn Gill came to the beach with her boyfriend. “We live in Bayview, and it’s super hot over there; it’s like 15 degrees hotter than it is right here at the beach,” Gill said. “Each year, it is getting hotter and hotter in the summers.”
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The early October heat wave broke daily records in many parts of the Bay Area with unseasonably high temperatures.
“Folks have been joking that it’s currently ‘Aug-tober,’” said climate scientist Daniel Swain.
“Literally, in many parts of the West, temperatures are, in fact, closer to August values than October values. And yet, here we are, the same month as Halloween, and we’re still talking about midsummer-like peak heat,” Swain said during his public office hours on Tuesday.
People gather at Robert W. Crown Memorial State Beach in Alameda, California, with the San Francisco skyline in the background on May 26, 2020. This week’s Bay Area heat wave, fueled by a persistent high-pressure ridge, is now expected to last through the weekend. Officials urge residents to stay hydrated and seek shade as temperatures remain elevated longer than forecast. (Ben Margot/AP Photo)
Although a fall heat wave is not unusual, the temperature highs, duration and far reach of this one are.
Such a trend tracks with what climate scientists have long expressed: Human-caused global warming has increased the frequency, length, intensity and reach of prolonged heat events.
Here’s what you need to know about the connection between heat waves and climate change in California and how extreme heat affects your health.
How much is California heating up?
On average, California has warmed by around 2.5 to 3 degrees Fahrenheit since the early 1900s. The rate of warming has accelerated over the past several decades relative to the mid-20th century.
In general, California’s inland regions are warming faster than statewide averages, and coastal areas are warming more slowly. Cold ocean water helps cool the coast, while inland mountains trap warm air.
The sun shines over towers carrying electrical lines in South San Francisco. With a Bay Area heat wave starting this week, California’s grid operator has ordered providers to delay maintenance to handle the surge in electricity demand. (Justin Sullivan/Getty Images)
Although it’s very hard for scientists to pin down exact numbers, heat events are projected to occur four to 10 times more often in the Northern Sierra region by 2050, for example.
Additionally, concurrent heat waves are happening more often. In the Northern Hemisphere, we’ve seen a roughly sixfold increase in the frequency of concurrent heat waves from 1979 to 2019.
How much longer are heat waves lasting?
By 2050, heat waves that negatively affect public health are projected to last two weeks longer in the Central Valley.
The length of the season (the number of days between the first heat wave of the year and the last) has increased as well. In the U.S., it’s up from about 40 days to roughly 70 — leaving people exposed to dangerous heat for longer.
How dangerous is extreme heat?
Extreme heat is the deadliest form of extreme weather in the United States, causing more deaths than any other weather-related hazard.
Extreme heat threatens our health. Higher temperatures are linked to negative pregnancy and birth outcomes, worse mental health and increased ER and hospital visits for ailments beyond heat stroke (cardiovascular disease, diabetes, respiratory illnesses).
Overnight temperatures are rising more quickly than daytime temperatures. That is dangerous because it limits our bodies’ abilities to cool off and recover before another day of heat arrives, leaving a person more prone to heat illnesses.
Adults over 65, children, people with disabilities, people with substance abuse disorders, pregnant people and those who lack access to cooling or work outside are the most vulnerable to extreme heat. Minority groups, historically redlined and urban communities are disproportionately exposed to heat. Low-income and unhoused people are also exposed.
How do I stay safe?
During a heat wave, stay hydrated, avoid strenuous activity and direct exposure to the sun, and check on your neighbors. Cool off with baths, showers or wet towels, and watch for signs of heat illness like cramps, headaches, nausea, tiredness or dizziness. Never leave kids or pets in a car, which can heat up quickly.
