NOAA tampers with US temperatures by actually altering the monthly data. This is because the US data set is robust and does not show any warming over the last century.
But with global temperatures they play a different game. Instead of relying on altering the data, they alter the station selection over time. By eliminating rural stations in the data set, NOAA and NASA increase the amount of warming.
You can get any shaped function you want out of the nearly useless “global” temperature data set. NOAA/NASA/CRU use a carefully cherry-picked common set of NOAA stations as their base, and then declare their data sets to be independent. But they keep changing the set of stations being used, which causes the changes over time seen in the animation above.
Transitioning to more heavily UHI infected data, gives them to freedom to create a hockey stick – while actually adjusting current global warming downwards.
It is clever ploy for several reasons:
- People like Steven Mosher look at the current data and convince themselves the adjustments are legitimate
- During Congressional hearings, Tom Karl simply shows graphs of how he is reducing warming
It is important for skeptics to be aware of the different games being played.