Los Angeles’ Rare Humidity Tied to Pacific Heat, Climate Change
Los Angeles isn’t the first place people think of as sultry in summer. But an unusually warm Pacific Ocean is pushing humidity to uncommon levels in a region better known for dry heat.
A marine heat wave stretching across the Pacific from the coast of Mexico toward Hawaii is warming the waters off Southern California, said Jennifer Francis, a senior scientist at the Woodwell Climate Research Center. The hot ocean may be the immediate cause, but a warming climate is the force behind it.
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“This marine heat wave has fingerprints of human-caused climate change all over it,” Francis said. “It isn’t sticky by East Coast standards, but it’s enough to make temperatures in the high 80s feel like the low 90s, which folks in LA are not used to.”
The unusually warm water is evaporating more moisture into the atmosphere, and a weak onshore flow is carrying that humidity inland, said Tom Kines, a meteorologist with AccuWeather Inc.
“Downtown LA has been getting close to 90F,” Kines said. “When you factor in the dew points it has been feeling like four to eight degrees higher than the actual temperature.”
Humidity makes hot weather feel even hotter, sending more people to air conditioners, boosting electricity demand and adding stress to power grids. It also raises health risks by making it harder for the body to cool itself through sweating.
AccuWeather calls humidity’s add-on effect the “RealFeel” temperature, while the US government refers to it as the heat index and Environment and Climate Change Canada cites it as the “humidex” in forecasts issued north of the US border.
If the temperature outside is 90F (32C), but the relative humidity is 60%, it is going to feel like 100F, the National Weather Service said. These calculations are just for shady areas, if a person is “exposed to direct sunlight, the heat index values can be increased by up to 15F.”
Further to the south, the Pacific waters near Peru and across the equator are warming as well as part of the growing El Niño many scientists say will be among the strongest on record. The warm waters off California are separate from that, Francis said, but they are part of a broader pattern of unusually warm oceans around the world. Marine heat waves have also emerged near Alaska and Siberia, across Hudson Bay and throughout much of the Mediterranean.
The warming oceans are adding another source of fuel to a Northern Hemisphere summer already marked by record heat, destructive wildfires and flooding.
“A strong El Niño is worrisome enough,” Francis said, “but the added influence of existing ocean hot blobs spells double trouble.”
Top photo: Visitors at Echo Park in Los Angeles on July 8. Photographer: Justin Sullivan/Getty Images. Bloomberg.