Former Virginia State Climatologist Patrick J. Michaels wrote an op-ed about his paper with Ross McKitrick from Canada’s University of Guelph in an American Spectator column today about the surface temperature record. This paragraph really caught my eye: “Weather equipment is very high-maintenance. The standard temperature shelter is painted white. If the paint wears or discolors, the shelter absorbs more of the sun’s heat and the thermometer inside will read artificially high. But keeping temperature stations well painted probably isn’t the highest priority in a poor country.”
The Stevenson Screen experiment that I had setup this summer is living proof of this.
Compare the photo of the whitewash paint screen on 7/13/07 when it was new with one taken today on 12/27/07. No wonder the NWS dumped whitewash as the spec in the 70’s in favor of latex paint. Notice that the Latex painted shelter still looks good today while the Whitewashed shelter is already deteriorating.
The whitewash coating I used was from a formula and method provided to me by a chemist at the US Lime Corporation, who is an expert on whitewash. He said the formula was true to historical records of the time when whitewash was used on the shelters. I was amazed to find that after just a few short months, my whitewash coating had lost about 40-50% of it’s surface area. Perhaps there was a mistake in the formula, or perhaps whitewash really is this bad at withstanding weathering.
In any event the statement of Patrick Michaels “Weather equipment is very high-maintenance. The standard temperature shelter is painted white. If the paint wears or discolors, the shelter absorbs more of the sun’s heat and the thermometer inside will read artificially high.” seems like a realistic statement in light of the photos above. The magnitude of the effect in the surface temperature record has yet to be determined, but it seems clear that shelter maintenance, or lack thereof, is a significant micro-site bias factor that has not been adequately investigated nor accounted for in the historical temperature record.
I’ll have more on this experiment soon including temperature time series graphs showing the difference between bare wood, latex painted, and whitewashed shelters.