Global Warming Helps Cool CA Coast, Study Finds

In a story that has yet to be covered by the San Diego Union-Tribune, the San Francisco Chronicle, or even the Los Angeles Times, this week the Ventura County Star featured on the front page (see here) a story about a San Jose State researcher, Robert Bornstein, who has found substantial evidence that global warming in California over the last fifty-plus years has led to a cooling along the coast in the summer.

Bornstein revealed his study at the state-funded California Climate Change Research conference. The curious can find his slides at the portal (along with numerous other studies).

The study is called Cooling Summer Daytime Temperatures in Coastal California during l948-2005: Observations and Implications for Energy Demand.

Two aspects of the study are especially striking for Ventura County residents.

First, Bornstein relies on a familiar causal mechanism to explain the cooling along the coast during the summer (which as he is quick to point out, is not an original idea). As summer heat warms California, inland areas become hotter than coastal regions, creating an onshore flow. Increased warming in the interior leads to stronger breezes. Stronger breezes lead to cooler temps along the coast.

The cycle is described more eloquently in David Carle’s "Air in California," from the UC Press:

Coastal marine climates are moderated by the local ocean temperatures: hot weather is "air conditioned" on summer days while cold winter days are warmed. The ocean is a very effective heat sink, storing heat during the day and then releasing at night when the air cools off…Weather and the climate in inland portions of California are shaped by a thermal low that forms in summer as heat rises out of the Central Valley and desert basins. The rising air creates low pressure that sucks marine air inland. Onshore sea breezes form after the land heats each day.

Second, this is not a model study. Bornstein has found evidence to buttress the claim. In the Carquinez Straits in the north of San Francisco Bay, he documents a strengthening sea breeze in the summer. Further, over the past forty years, even as inland California overall has warmed (by about 1 degree Fahrenheit, or .57C, according to a 2006 paper from the climate center), coastal California has slightly cooled (by about .25C per decade).

This is not an enormous number, but it’s hugely good news for Californians living not too far from the ocean, in places such as the Bay Area, Los Angeles, and Ventura County. Will follow up asap. For now, here’s a map of summer of warming in SoCal over the last forty years (from Bornstein’s slides).

Note the mostly rising temps inland, and the cooling temps along the coast…

Temps_in_socal_19752005

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