After yesterday’s post on the record number of days with a warm night in New Orleans, some of my meteorologist friends and I have been discussing why there might be such a drastic change.  My friend Scott Lindstrom from the University of Wisconsin-Madison posted the graph below, which shows a step function change in the number of nights at or above 75 F at New Orleans right around 1996.  Did the climate change drastically at that point?  Coincidentally (or not), the New Orleans airport changed instruments on May 1, 1996 to a new automated gauge called ASOS for Automated Surface Observing System.

So now the question is, how was the climate record changed by the new instrument?  This is one of the problems that climatologists have in looking at long climate records, because things like station moves and changes in instrumentation can affect the climate record regardless of whether the climate is really changing or not.  I’ve sent a letter to the author of the Capital Weather Gang blog post; I will let you know what I find out.  Stay tuned!