NASA has repeatedly altered global temperature data, causing a net doubling of 1880-1980 global warming since their 1981 version. Pre-1965 years keep getting colder, and post-1965 years keep getting warmer. (Note that prior to 2003, NASA did not even pretend to know pre-1950 ocean temperatures.)
This is on top of the changes Hansen had already made by 1981, erasing half of the 1940-1970 cooling. Since 1981 they have erased the rest of the 1940-1970 cooling.
One thing driving this is the disappearance of truly rural stations, which is causing more and more UHI damage to the temperature record.