Some time ago a study was funded by a number of organizations and individuals, including some who are famously skeptical of global warming (such as the Charles G. Koch foundation) in order to see if urban heat island effects could explain the famous “Hockey Stick” curve. The study was supposed to be non-biased, and it may well be, but if there are any biases they would likely be in favor off anti-Global Warming thinking, or perhaps “pro-denialist” or “anti-warmist” … pick your term.
Well, just moments ago, the study was released and the findings are quite interesting.
The pre-publication version of the study’s abstract says the following:
The effect of urban heating on estimates of global average land surface temperature is studied by applying an urban-rural classification based on MODIS satellite data to the Berkeley Earth temperature dataset compilation of 39,028 sites from 10 different publicly available sources. We compare the distribution of linear temperature trends for these sites to the distribution for a rural subset of 16,132 sites chosen to be distant from all MODIS-identified urban areas. While the trend distributions are broad, with one-third of the stations in the US and worldwide having a negative trend, both distributions show significant warming. Time series of the Earth’s average land temperature are estimated using the Berkeley Earth methodology applied to the full dataset and the rural subset; the difference of these shows a slight negative slope over the period 1950 to 2010, with a slope of -0.19°C ± 0.19 / 100yr (95% confidence), opposite in sign to that expected if the urban heatisland effect was adding anomalous warming to the record. The small size, and its negative sign, supports the key conclusion of prior groups that urban warming does not unduly bias estimates of recent global temperature change.
Emphasis mine. Sorry to spoil the ending of Greg’s post, but the urban heat island effect cannot explain global warming, because the urban heat island effect is actually waning for some reason. Another hypothesis bites the dust. Which is really horrible — anything that mitigates the proof that global warming is happening would be most welcome at this point.
Wickham, C., Curry, J., Groom, D., Jacobson, R., Muller, R., Perlmutter, S., Rohde, R., Rosenfeld, A., & Wurtele, J. (2011). Influence of urban heating on the global temperature land average using rural sites identified from MODIS classifications Unknown