SEARCH BLOG: GLOBAL WARMING
Recently, I posted information regarding a grass-roots effort started by Anthony Watts who started examining the locations of the weather monitoring stations that record official temperatures. This effort first came to my attention when Dr. Roger Pielke, Sr. at Climate Science posted it to his site.
Since then, the attention to the condition of these monitoring stations has grown. I happened to be working on my porch the other evening when I noticed a significant discrepancy between the reported temperature and that being measured by the thermometer on my porch. After sunset the variance became much smaller. I speculated that there may be conditions around the local reporting sites that overstated the temperatures... possibly the Urban Heat Island effect. If the reporting sites are situated where the surroundings can absorb or reflect heat, the stations are likely to exaggerate the actual heat in the air.
For example, right now (10:30 am) the reported temperature is 73 degrees and my porch thermometer reads 72 degrees. I'll concede that it may be the inaccuracy of my thermometer. As the day proceeds, however, the variance increases.
Note this chart from Climate Audit:
The horizontal axis is in minutes from midnight (took me a few minutes to figure that out). This plots the difference in temperature readings just varying the coatings on the weather station. It does not demonstrate the effect of locating the station above asphalt or next to buildings or parked vehicles.
I can't really explain why air temperatures (black line) are higher in the pre-dawn and post-sunset hours than the stations. Steve McIntyre at Climate Audit may be able to shed light on that. You may want to go to the link above the chart to read the many comments regarding this issue.My own observations parallel Steve's in that pre-dawn and post-sunset hour readings on the porch are higher than the reporting station. That may be due to some heat trapped by the house radiated out to the porch.
Southern facing porch
Area surrounding porch
The thermometer is located just to the left of this picture's edge and at the top of the screen. Therefore, the readings are always in the shade and essentially open-air. This, it seems to me, represents a "true" temperature reading for the location.The point of all of this is that with weather data recording and real estate, the important factor seems to be... location, location, location.
If, as Anthony Watts' effort shows, weather monitoring stations are poorly located and giving exaggerated heat readings due to Urban Heat Island effects, then the whole contention of recent global warming (corresponding to expansion of Urban Heat Islands around weather stations) is brought into serious question... especially when recent data is compared to data many decades ago that were captured under conditions closer to that of my porch...