In 1975, the National Academy of Science reported half a degree cooling from 1940 to 1970
This wrecked global warming theory, so NASA simply made the cooling disappear.
The NASA fraud enabled Michael Mann’s hockey stick fraud. Once the 1940-1970 cooling was disappeared by NASA, Mann claimed that tree ring proxies suddenly stopped working after 1960 – and deleted them from his temperature reconstruction.
That was stage one of the biggest science fraud in history. But then Mann added insult to injury by using massively tampered post-1960 NASA data to build the rest of the hockey stick.
Creating the hockey stick required large scale collusion and fraud by government agencies and academia. The fact that other academics and the IPCC were willing to accept the idiotic claim that tree rings suddenly stopped working after 1960, shows that that they are morons and their opinions are worthless.