As of 1999, GISS showed that US temperatures (red) closely tracked 1975 National Academy of Sciences Northern Hemisphere temperatures (blue.) They both peaked around 1940 and declined rapidly thereafter.
Hansen was concerned that the US wasn’t warming like it was supposed to.
Whither U.S. Climate?
By James Hansen, Reto Ruedy, Jay Glascoe and Makiko Sato — August 1999
How can the absence of clear climate change in the United States be reconciled with continued reports of record global temperature? Part of the “answer” is that U.S. climate has been following a different course than global climate, at least so far
This was just before the hockey stick was invented, and in order to get rid of Briffa’s trees they had to create a divergence between US and global temperatures, and they had to make the post-1940’s cooling go away. They did just that, and now have almost completely eliminated the 1940’s warming spike. Current GISS northern hemisphere is in red below, normalized to the late 1960’s.
Simultaneously, they worked over US temperatures and made the Dust Bowl disappear. Graphs below have the five year means normalized to the most recent common date of 1997.
Bottom line is that Northern Hemisphere and US temperatures peaked in the 1930’s and 1940’s – and the hockey stick is government scientist manufactured junk science.
Extra credit. As of 1978, NOAA also showed strong southern hemisphere cooling, which GISS has completely eliminated and turned into a warming trend.
The graph below shows GISS southern hemisphere temperatures in blue, vs. 1990 IPCC southern hemisphere in black.