California fog levels decline due to climate changes

Fog levels in the San Francisco Bay Area have decreased by 34.5 percent over the past century, resulting in approximately three to four fewer hours of fog per day. This decline follows a broader trend observed across California, including a reported 33 percent decrease in 2010.

Researchers suggest the reduction is driven by a shrinking temperature gap between coastal and inland regions. As the temperature difference weakens, the atmospheric pull that draws cool, foggy air toward the land diminishes. Additionally, warming Pacific Ocean waters and weaker coastal winds have reduced the upwelling of cold water necessary for fog formation.

The loss of fog poses a significant threat to coastal redwood forests. According to UC Berkeley professor Todd Dawson, fog can provide 30 percent or more of a redwood tree’s annual water intake and helps prevent dehydration by maintaining air moisture during rainless summers.