From 1900 to 1940, US summers warmed at a rate of 5F per century. Then they cooled until 1960. Since 1960, they have been warming at a rate of 3F per century.
1936 is still officially the hottest summer, even though USHCN adds 0.6F on to all recent US temperatures.
summer of 1940 usa tempuratures
“20TH”!!! 19TH Century was the from 1801 to 1900!
# 1910-1940 Warming Was Faster #
The warming was an arctic warming, which started in winter 1918/19 around Spitsbergen, brought a warming to the Northern Hemisphere that lasted in the USA until about 1933, ( http://www.arctic-warming.com/ ) in Europe until the first WWII winter 1939/40, as explained in detail at: http://climate-ocean.com/