An analysis of 1970–2005 observed summer daily maximum and minimum temperatures in two California air basins showed concurrent daytime coastal cooling and inland warming. To study the impacts of these results on energy consumption, summer cooling degree day (CDD) and winter heating degree day (HDD) trends were analyzed via these temperatures. The 2 m level air temperatures consisted of data from 159 locations in California, each with daily minimum and maximum values. Primary data sources included Cooperative Weather Station Network sites, first order National Weather Service stations, and military weather stations. An analysis of the CDD and HDD data has been undertaken for California, in general, and the San Francisco Bay Area and South Coast Air Basin, in particular, as the source of data for an analysis of energy-demand trends. Regional climate fluctuations have considerable effects on surface temperatures, which in turn affect CDD and HDD values. An asymmetric increase in summer CDD values between coastal and inland regions of California was found during the last 35 years, while winter HDD values showed decreases in most of California. In general, coastal areas experienced decreases of CDD, while inland regions experienced increases. The summer asymmetric increases in CDD is attributed to intensified sea breeze flows, which suggests increases in cold marine air intrusions over coastal land masses due to an increased regional sea breeze potential, which ventilates coastal areas, helps reduce maximum temperatures, and contributes to CDD decreases. An analysis of energy demands in the two air basins supports these climatological findings.