Global Warming Science:


California Fog


[last update: 2010/02/16]



Studies show that global warming will increase the coastal fog. Studies also show that global warming has decreased coastal fog. Global warming causes everything.



The Global Warming Foggy Contradiction


San Francisco Chronicle: 2009/07/06 – More Fog due to global warming



“Get ready for even foggier summers”: The Bay Area just had its foggiest May in 50 years. And thanks to global warming, I’s about to get even foggier. Scientists began sounding the alarm 20 years ago… the theory then and now, is that the hotter the Central Valley gets, the greater the temperature and pressure gradients between the inland and coast – therefore forming more fog.”




The Telegraph: 2010/02/15 – Less Fog due to global warming



“Fog over San Francisco thins by a third due to climate change”: The coastal fog along the Californian coast has declined by a third over the past 100 years … the temperature difference between the coast and interior has declined substantially in the last century, in step with the decline in summer fog … If the fog is gone, we might not have the Redwood forests we do now ”





The Data


The studies refer to “the temperature difference between the coast and interior”. The following two figures show the average May / June / July temperature for coastal Santa Cruz, which is a foggy area (top) and the non-foggy Merced Municipal airport in the interior Central Valley approximately due east of Santa Cruz (bottom). The map indicates the relative position of Santa Cruz and Merced.





The following figure compares the same data as in the above two graphs with Merced changed to red and Santa Cruz in blue. There is virtually no difference until after 2000. Except for the year 2000 at Merced, recent warming was similar to the 1930s. The warmest summer in Santa Cruz was 1992.





More fog? Less Fog? More smoke and mirrors.




The New Study


The Telegraph article shown above reports a new study to be published in the Proceedings of the National Academy of Sciences, and also described in Science Daily [], which stated: “evaluated the data from airports along the northern California coast and found two airports -- Arcata and Monterey -- that had consistent fog records going back to 1951.” Unfortunately they don’t understand the climate of the US – any data set that does not go as far back as 1930 will provide a misleading analysis.


The article states: “Since 1901, the average number of hours of fog along the coast in summer has dropped from 56 percent to 42 percent, which is a loss of about three hours per day … the change could affect not only the redwoods, but the entire redwood ecosystem” Alarm! Alarm! Nothing has ever changed before, in the thousands of years that redwoods have been there!


The article states that they “demonstrated that the coast-inland contrast has decreased substantially, not just in Northern California, but along the entire U.S. coastline from Seattle to San Diego. This change is particularly noticeable in the difference between Ukiah, a warm Coast Range site in Northern California, and Berkeley on San Francisco Bay. At the beginning of the 20th century, the daytime temperature difference between the two sites was 17 degrees Fahrenheit; today, it is just 11 degrees Fahrenheit.”


It is not clear why they compare Ukiah and Berkeley – the annual average May / June / July temperature is shown below along with a map indicating the relative position.





More reasonable comparisons would be based on stations located on the coast / inland from each other, such as Santa Cruz / Merced shown previously, or Eureka / Redding as shown below. The graph shown below also shows the problem of using data sets starting in 1950 instead of earlier in the century. The coast / inland contrast may be different than in the 1950s – 1960s, but it is similar to the first 40 years of the 20th century.