As of 1974, climate experts showed a strong temperature spike around 1940, followed by plummeting temperatures until the 1970s, with 1970 actually cooler than 1900.
Once the climate scam changed from global cooling to global warming in the late 1970s, climate experts started removing the spike. The graph below is from Hansen, 1981
Figure 2-1. Global temperature trend for (a) past century, (b) millennium, and (c) 25,000 years. (a) is based on J. Hansen, D. Johnson, A. Lacis,
S. Lebedeff, P. Lee, D. Rind, and G. Russell, 1981
Originally located at : http://www.epa.gov/climatechange/effects/downloads/Challenge_chapter2.pdf
Climate scientists later renamed the spike a “blip” and expressed their desire to get rid of it – without even knowing what caused it.
And that they did. The graph below plots current NASA global temperatures along with their 1981 version.
The next graph shows the hockey stick of changes to published NASA global surface temperature since 1981
The hockey stick has nothing to do with the climate, and everything to do with altering the data.