The general idea is that global temperature measurements are primarily based on temperature sensing devices in cities. Cities themselves likely are getting warmer, as they have more light, thermal, water and chemical pollution. The thermal pollution could be coming from the amount of concrete and other insulating materials used to build cities. These “Insulators” absorb heat during the day and radiate it at night, thus giving the appearance of having increase low temperatures around them.
This is, however, extremely local in character and is strictly limited to cities and their immediate environs. The total land mass relative to the land area represented by cities is so large that any amount of “Thermal pollution” is diminished quickly as one gets away from the area where the temperatures are measured. Temperatures have been measured at city centers or areas where there is a significant amount of chance for thermal pollution to occur, such as airports, or harbors or such. We happen to live close to where temperature is recorded for one part of Los Angeles, just south of LAX.
I have noticed, ever since moving back here (near 3 years ago now) that the nighttime temperatures recorded at LAX are much of the time a few degrees higher than what I see on my thermometer in our back yard. We are probably a little closer to the ocean where we are, but I would guess that we are still within the same “Microclimate.” thus, for the longest time this puzzled me to no end. Those discrepancies in readings are consistent across all seasons pretty much.
Then last night it dawned on me that is a possible “Solution” to the Global Warming problem in that it is actually the source of the “false” temperature measurements. Those bad temperature readings get plugged into the Climate models and thus we have bad weather predictions. We are not seeing “global” increases in temperature but rather as cities get more and more concrete and other types of insulators around them their local temperature is increasing – especially at night when low temperatures are recorded. This variation due to the insulation effect quickly diminishes with distance from the city center. Our house is barely three miles south of LAX, and we have a lot less concrete around us in general.