In 1999, NASA showed no net global warming from 1876 to 1976. This wrecked their hockey stick plans, so NASA erased all of the inconvenient pre-1880 data and cooled 1880 temperatures by about 0.2C.
This abuse of science is atrocious, but it gets worse. The NASA data had already been highly corrupted in 1999. In 1974, the National Center For Atmospheric Research (NCAR) showed 0.4C cooling from 1940 to 1970, and no net warming from 1870 to 1970.
NASA has since erased this cooling, and now shows 1940-1970 as warming.
The 1940 to 1970 global cooling was also reported by CRU, and they blamed droughts, floods, blizzards and tornadoes on it.
But the fraud gets much worse. Briffa’s trees showed the 1970’s as one of the coldest periods in the last 600 years. So Michael Mann completely erased them when he created the hockey stick.
In 1981, NASA still showed about half of the 1940-1970 cooling, which they have since erased.
The only hockey stick, is the hockey stick of data tampering.
Global warming is indeed Mann-made, by Michael Mann and James Hansen. But it has nothing to do with climate or science.