The Hottest Summer Days in D.C. Have Not Gotten Hotter in Last 40 Years... - Roy Spencer, PhD

…but the coolest summer nights have warmed by 5 deg. F.

My interest is in determining how much the urban heat island (UHI) effect has impacted reported warming trends. 

• Last year we published a paper using population density as a proxy for urbanization, and found that about 60% of U.S. urban and suburban warming trends...could be accounted for by urbanization.
• But we also found that relationship largely disappeared by the 1970s, with little warming since then being accounted for by increases in population density...

The results surprised me...

• What is amazing is that the coolest summer nights in DC have warmed 10 times faster than the hottest summer days..
• But look at those nighttime temperatures! The coolest nights have warmed by almost 5 deg. F in the last 40 years. This is clearly dominated by the UHI effect, since climate models tell us that days and nights should be warming at much closer to the same rate.