The graph you posted of the ratio of high and low temperatures was cherry picked and deceptive. Ratios tell nothing if you don’t have the actual numbers to look at. Here are the number of new highs and lows per decade prior to 1950 in the states. Note the ‘30’s.

year highs lows ratio
1910 65 54 1.2
1920 41 48 .85
1930 117 57 2.051940 37 55 .67

2000 19 7 2.7

Let’s see 19 is the 2000’s and 117 in the 1930’s which is bigger. Ratios without actual numbers is deceptive. Starting in 1950 in a cooling trend was cherry picking a start date. The authors could have easily gone back to 1910 or 1880 if they were not disposed to show a warming trend from the 1940-1970 cooling trend.