NASA massively tampers with US temperature data to turn a post 1930 cooling trend into a warming trend.
The graph below shows the hockey stick of data tampering they are doing. Notice what they did between 1970 and 1990. They introduced a huge amount of random noise, in an attempt to hide the tampering.
If you overlay the 1999 (green) and 2015 graph (red) they appear at first glance to be quite similar. The noise they introduced makes it difficult to see the magnitude of the tampering.
In order to expose their fraud, I generated the two images at the top of the page. But another view which shows what they are doing is below. I normalized the five year mean lines to the most recent common years. In this view it becomes clear how they massively cooled the past, to make the cooling trend disappear.
The random noise from 1970-1990 makes no sense from a physical point of view. People aren’t moving stations back and forth every other year. Its only purpose is to hide their criminal activity.