The Identification of distinct patterns in California temperature trends

Regional changes in California surface temperatures over the last 80 years show distinctly different spatial and temporal patterns in trends of maximum temperature (Tmax) compared to trends of minimum temperature (Tmin). For annual trends computed since 1918, Tmin is warming much faster than Tmax. However, since 1970 the warming has not only accelerated, but increases in Tmin and Tmax have been of similar magnitude. Observations show coherent statewide positive trends in Tmin. By contrast, trends in Tmax tend to vary on finer spatial-temporal scales. Regional Tmax trends show that the interior southern parts of California are experiencing the most rapid warming in the last 35 years, especially during spring. Conversely, regional cooling trends in Tmax since 1970 are evident in winter and summer at both regional and local levels. A discussion of the various forcing mechanisms potentially responsible for the distinct changes in trends for Tmin and Tmax as well as an outline of various diagnostics that can be used in climate model attribution studies will be discussed.