The effect on U.S. average temperature is about 0.15°C beginning in 2000. Does this change have any affect whatsoever on the global warming issue? Certainly not, as discussed below.
What we have here is a case of dogged contrarians who present results in ways intended to deceive the public into believing that the changes have greater significance than reality. They aim to make a mountain out of a mole hill. I believe that these people are not stupid, instead they seek to create a brouhaha and muddy the waters in the climate change story. They seem to know exactly what they are doing and believe they can get away with it, because the public does not have the time, inclination, and training to discern what is a significant change with regard to the global warming issue.