The US National Oceanic and Atmospheric Administration (“NOAA”) has a great website that is well worth a visit. The chart below, interactive on the NOAA site, shows average May temperatures for the continental US since 1895.  It can be seen that while there is a high degree of fluctuation, the temperature regularly reverts to the average.


Chart courtesy NOAA

This is only one set of data and so does not necessarily negate the “Global Warming” hypothesis. However, it is worth some thought. Some other reading that may be of interest:

In sum, I do not think we understand anywhere near all the variables that contribute to climate, either today or in the future. Expensive measures to combat carbon dioxide levels, for example, will almost certainly prove to be quixotic.