The Science Behind the Effects of Climate Change in California

Extreme weather events from intense wildfires to heavy rains have plagued California, the nation’s most populous state, in recent years. The deadliest wildlife in state history, the Camp Fire, killed 85 people and destroyed over 90 percent of homes in Paradise, a small town in a rural region 90 miles north of the state capital of Sacramento, in 2018.

In Santa Rosa, the biggest city in Sonoma County wine country, the Tubbs Fire killed 22 people and burned over 5,000 homes in late 2022 in the Coffey Park subdivision. A year ago, San Francisco was drenched by the second-biggest amount of rain in 174 years of record-keeping, 5.5 inches on December 31, 2022. Ironically, California was heading into its fourth year of drought at the time, but in the next three weeks over 11 inches of rain on average poured over the state, 32 trillion gallons, causing evacuations due to floods and downed trees in Santa Cruz and Monterey counties on the central Coast. 

In March 2023, a rainstorm killed at least five people were killed in the Bay Area, while floods damaged over 900 homes and businesses in the Monterey town of Pajaro, after a river levee broke. In all, 31 “atmospheric rivers” of rain hit from October to late March – several classified as “100-year events,” meaning their occurrence was only once a century – says the Scripps Institute of Oceanography’s Center for Western Weather and Water Extremes.

As 2023 was the hottest year ever in world history – about 2.63 degrees F warmer on average compared to pre-industrial times (two November days were 3.6  degrees F warmer) – the trend is expected to continue, says the United Nations’ Weather Meteorological Organization and Europe’s Copernicus Climate Change Service.    

Dr. Daniel Swain, a climate scientist at the University of California, Los Angeles, Institute of the Environment and Sustainability, and National Center for Atmospheric Research, studies the effects of climate change, particularly in California and the Western U.S. He uses the analogy of a  kitchen sponge to explain the science behind the “expanding atmospheric sponge effect.”

“As temperatures rise, the water vapor-holding capacity of the air increases exponentially, at 3-4% per degree F of warming. This increases not only the ceiling on precipitation – i.e. when it’s raining, more extreme rainfall and potentially larger and more severe floods – but also on evaporation, i.e. more demand for water by the atmosphere, increasing the propensity of the air to literally extract moisture back out of the land surface, plants, and bodies of water,” says Swain, the host of WeatherWest, a YouTube channel on climate change. That’s the main reason why California droughts have become more severe, and will keep doing so in a warming climate caused by higher carbon dioxide emissions, and why California is seeing much larger, more intense, and destructive wildfires.     

“When vegetation is drier it burns more readily, more intensely, and hotter, leading to faster-spreading and more severe fires,” he adds. California has always alternated between dry and wet years, he notes. “The name of the game in California is increasing hydroclimate whiplash. Extreme rainfalls and potential flood risk are worsening, while drought and wildfire events are becoming more intense. They’re two sides of the same thermodynamic coin.”