URBAN BIAS INFLUENCES ON LONG-TERM CALIFORNIA AIR-TEMPERATURE TRENDS

An analysis of 80-year shelter level temperature records at 112 California sites has been carried out. Results show that sea surface temperature (SST) and urban heat island effects influence the magnitude of the observed warming trend in the overall data set. These effects, however, are masked by averaging all temperature records together. While a warming trend existed in the overall data set, areas with such trends generally corresponded to areas containing the state's major population centers. Warming trend magnitude also increased with county population size, and 20 small inland towns and rural areas actually showed cooling trends. SST trends over the last 40 years showed cooling in mid-ocean areas and an anomalous warming at coastal sites. The warming was associated with a decline in the normal frequency of cold water upwelling in the coastal area. SST warming was found to be highly correlated with the warming of shelter level temperatures at coastal land observation sites.