Trends in Extreme United States Temperatures

• Activity Number: 602
• Type: Contributed
• Date/Time: Wednesday, August 7, 2013 : 2:00 PM to 3:50 PM
• Sponsor: Section on Statistics and the Environment
• Author(s): Jaechoul Lee*+ and Shanghong Li and Robert Lund
• Companies: Boise State University and Clemson University and Clemson University
• Keywords: Autocorrelation ; Changepoints ; Generalized Extreme Value Distribution ; Genetic Algorithm ; Head-Banging ; Periodicity

Abstract

This paper develops trend estimation techniques for monthly maximum and minimum temperatures observed in the conterminous 48 United States over the last century. While most scientists concur that this region has warmed as a whole, there is no a priori reason to believe that temporal trends in extremes will have same patterns as trends in average temperatures. Indeed, under minor regularity conditions, the sample partial sums and maximums of stationary series are asymptotically independent. Climatologists believe that minimum temperatures are warming most rapidly; such an aspect can be investigated via our methods. Here, models with extreme value and changepoint features are used to estimate trend margins and their standard errors. A spatial smoothing is then done to extract general structure. The results show that monthly maximum temperatures are not significantly changing -- perhaps surprisingly, in more cases than not, they are cooling. In contrast, the minimum temperatures show significant warming. Overall, the Southeastern United States show the least warming (even some cooling) and the Western United States, Northern Midwest, and New England have experienced the most warming.