GISS uses an insidious trick to hide their data tampering. They cool pre-1963 years, and warm post-1963 years. This makes their data tampering look much less severe than it actually is. A better visualization is to normalize the graphs to the most recent common data, and show the total magnitude of the tampering. The animation below shows that.

2003 version

http://www.giss.nasa.gov/data/update/gistemp/graphs/Fig.Anew.ps

2014 version

Fig.A.gif (656×446)