Heat waves will roast Bay Area, study says
Summers in San Francisco may soon feel more like the warmer East Bay. The East Bay may soon feel more like Sacramento. And Sacramento — well, it might just be too hot to stick around any longer.
One of the most detailed studies on rising temperatures suggests that few places in the United States will be unaffected by extreme heat by the middle of this century. Without significant steps to curb global warming, most of the nation will see more than twice as many days when the heat index, or “feels like” temperature, exceeds 100 degrees, according to the study released Tuesday by the Union of Concerned Scientists. Many spots will see several more days.
Even places with relatively moderate climates, such as the Bay Area, will begin to experience uncomfortable and even dangerous spikes in temperatures, the study concludes. Livermore will go from averaging one day a year with a heat index above 100 degrees to seven days by 2050. Napa will go from averaging no 100degree
days to six during this period. And Morgan Hill will jump from zero to five.
Scientists warn that such bouts of hot weather can lead to heatrelated illnesses, and even deaths, a concern that is as valid in the Bay Area as warmer locations because many of the region’s buildings lack air conditioning. Extreme heat can also cause lapses in labor productivity, food supplies and economic growth.
“It’s clear that we need to focus on heat as a key impact of climate change,” said Kristie Ebi, a professor of global health at the University of Washington, who was not affiliated with the new study but reviewed it. “Heat waves are going to increase in intensity and duration. It affects everyone. It cuts across the U.S. population in a way that flooding, sea level rise and drought don’t.”
The study used climate models to simulate how rising temperatures will affect specific geographic areas, including 57 places in California. The authors projected how much extreme heat each spot can expect, and when, under different levels of greenhouse gas emissions.
While nations across the globe are working to cut emissions, most scientists say the reductions aren’t happening quickly enough to prevent widespread harm. Climate action in the United States has been slow under President Trump, who has called global warming a hoax.
If nations continue to make only limited progress — allowing the planet’s average temperature to increase by 4.3 degrees Fahrenheit by 2100 — the study finds that the nearly 500 places evaluated nationwide will see an average jump in the number of days with a heat index of 100 or more from the historical 14 per year to 30 per year by 2050. The number of days with a 105degree heat index will rise from five to 18 by midcentury.
If no progress is made on climate change, the number of days with extreme heat is projected to go even higher — 36 days at more than 100 degrees and 24 days of at least 105 degrees.
The National Weather Service, which uses the heat index to warn the public about hot weather, generally issues a heat advisory when the index is expected to reach or exceed 100 degrees for 48 hours. A heat warning is issued when the metric is likely to be 105 degrees or more for 48 hours.
California has historically had nine days per year with a 100degree heat index or higher. That is expected to become 21 days by 2050, according to the study. The state’s three days historically with a heat index of 105 or more will rise to nine.
“The results were more dramatic than I expected,” said Kristina Dahl, senior climate scientist for the Union of Concerned Scientists and lead author of the study. “If we fail to reduce heattrapping emissions, there will be a staggering expansion of dangerous heat.”
The impact will be worst in parts of south Texas, where the study projects cities like McAllen and Brownsville will see more than four months with a heat index of at least 100 degrees by 2050. California’s Coachella Valley (Riverside County) and Imperial Valley (Imperial and Riverside counties) aren’t far behind, with both expected to experience as much as 3½ months of similarly oppressive heat by the midcentury.
In Northern California, Redding is projected to have 39 days per year with a heat index of 100 degrees or more by 2050. Yuba City (Sutter County) will have 34 days per year, and Sacramento will have 24 days.
Cooler San Francisco will see its historical average of zero days per year with a heat index of 100 degrees or more edge up to one day over the next 30 years. San Jose will go from zero to two.
“The Bay Area has historically had a moderate climate, but some of the recent heat waves we’ve experienced have shown how vulnerable we are to extreme heat,” Dahl said. “When you look at a list of cooling centers that are available in the area, the list is fairly limited, and in libraries, it (cooling) will be only a specific room. We’re really not equipped to deal with even what I would call moderate extreme heat, like temperatures above 90.”
Already this year, San Francisco flirted with 100degree temperatures during a spree of unusually hot weather in June.
The Union of Concerned Scientists is a nationwide coalition of researchers who study and advocate for fixes to the nation’s most pressing problems. The group’s recent work was published in the journal Environmental Research Communications.