In 1976, National Geographic showed a strong cooling trend from 1938-1976, and showed that 1976 was no warmer than 1880
NASA has since altered the data to remove the 1940s blip.
Analysis of warming since 1881 shows most of the increase in global temperature happened before 1919 — before the more re-cent sharp rise in the amount of carbon dioxide in the atmosphere. said Thomas Karl, of the National Oceanic and Atmospheric Administration’s National Climatic Data Center in Asheville, N.C. While global climate warmed overall since 1881, it actually cooled from 1921 to 1979, Karl said
This was a critical part of hiding the decline.