Temperature Change in the Contiguous 48 States Between 1901 and 2020

Abstract

Climate change has become a global emergency.  Many people have studied the rise in temperatures over the last few decades.  But few have studied how monthly average temperatures at the state level in the United States have changed for more than a century.

The authors divide the 120-year period January 1901 to December 2020 into two 60-year periods and then compare the monthly average temperature in each period for each of the 48 contiguous U.S. states.  When these data are divided into seasons, the largest changes are observed for winter (December, January, ad February) and summer (June, July, and August) months, especially among states that have coastal access to the Pacific Ocean or the Atlantic Ocean in the northeast. 

Apart from presenting a series of two-sample t-tests for each of the 48 states for all seasons combined and one for each of the four seasons, the authors also present color-coded maps summarizing the statistical results for the winter and summer seasons.  The maps use the p-value of each two-sample t-test to show which states in each season between the two 60-year periods are getting cooler (green, light blue, dark blue) and which states are getting warmer (yellow, orange, red).