The International Panel on Climate Change (IPCC) has a 1990 report that uses NOAA data from 1974. It shows that Arctic sea ice is cyclical, as it's always been, and had a peak in 1979. SO NOAA was measuring sea ice extent at least as far back as 1974.

https://web.archive.org/web/20120428072521/https://www.ipcc....

Also, the third graph on page 202 shows that the Earth was MUCH warmer a thousand years ago than it is now, despite far less CO2. This isn't particularly surprising since carbon dioxide levels track global temperature - not the other way around - as the ice core data going back 800 000 years shows.

The 1985 Department of Energy report Projecting the Climatic Effects of Increasing Carbon Dioxide uses data going back to 1925 that shows, surprise, that Arctic sea ice is normal, cyclical and has nothing to do with CO2 levels.

https://www.researchgate.net/publication/236534420_Projectin...