Yep, I admit it, air conditioning may indeed be causing us to measure higher temperatures. Here is the historic temperature plot of Detroit Lake, MN, one of the thousand or so measurement points in the data base that is used to compute historical warming in the US.
Look at that jump in the last 10 years. It must be global warming! Can't possibly be due to these air conditioning units installed around 2000 and venting hot gas on the temperature instrument (in that round louvered thing on the post).
More from Anthony Watts, who is leading the effort to document all these stations. You too can help. The odds are you live less than an hour from one of these stations -- take your camera and add it to the data base. Its fun!
Incredibly, the global warming community still argues that documenting the quality of the installations used in the official global warming numbers is unnecessary. More air conditioners blowing on official temperature measurements here. Worst temperature installation found to date here, "coincidently" at the site with the highest measured 20th century warming.