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Several critically important temperature thresholds are experienced in the climate of the desert southwest USA and in central Arizona. These thresholds present significant and increasing challenges to social systems. Utilizing daily surface air temperature records from Phoenix and Gila Bend regional weather stations from 1900-2007, we examined 3 temperature thresholds: (1) frost days (minimum temperature < 0 degrees C); (2) misery days (maximum temperature >= 43.3 degrees C); and (3) local characteristics of heat waves. We investigated historic climate patterns in addition to considering the human implications associated with these changes. Analyses also integrated multidecadal modes of the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Key findings of this study were (1) uneven warming trends among temperature thresholds between the Phoenix (pronounced warming) and Gila Bend (modest warming) weather stations; (2) disjointed associations between ENSO and PDO with frost and misery days, signaling anthropogenic interference between temperature thresholds and historic atmospheric processes; (3) variable effects of ENSO and PDO modulations on annual frost and misery days; (4) evidence of urbanization suppressing local effects of global climate systems (i.e. ENSO, PDO); and (5) potentially significant and widespread adverse impacts on many local environmental, economic, and social systems as a result of changes in threshold temperatures.