Urban areas can be warmer than surrounding non-urban areas because there is a lot of combustion, pavement and other structure can collect solar heat and retain it for a while, and other factors. It is not uncommon to look at a weather map where conditions for precipitation are marginal, and everywhere but the urban zone, or only the urban zone and nothing else, is showing a weather phenomenon. Because people and airports (where weather is very important) are located in or very near urban areas, it stands to reason that a lot of the data used to estimate global temperatures would be affected by any urban effects, and if urban areas are a) warmer than surrounding areas and b) increasingly warm over time then “global warming” may well be an artifact of the urban heat island effect. That wouldn’t necessarily make it a hoax, but it would make it wrong. We would then have to revise our understanding of certain aspects of physics because we expect global warming to occur in CO2 levels go up, but physics has been revised before. Kepler was wrong, Newton was wrong, maybe the climate change scientists are wrong too.
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. I have to admit, I was not expecting these findings at all, and they have caused me to change my mind about certain things. Which is fine, because that is how science works, but still, I was rather shocked.
The paper, just released, is called “Influence of Urban Heating on the Global Temperature Land Average Using Rural Sites Identified from MODIS Classifications” and was carried out by Charlotte Wickham, Judith Curry, Don Groom, Robert Jacobsen, Richard Muller, Saul Perlmutter, Robert Rohde, Arthur Rosenfeld, and Jonathan Wurtele.
The study provides an overview of the previous “warmist” literature in which so-called climate scientists have made the claims that the Urban Heat Island effect is non-existent, that it is small so don’t worry about it, or that they’ve “adjusted” for “it.” They then take the largest possible data set available and compare all of the known Urban Area data with rural data to see if there is a difference in so-called “Global Warming” when looking at the two, and especially, if there is a change over time in the effect that might explain, for instance, the dramatic upswing in temperatures that makes the so-called “Hockey Stick” look like a so-called “Hockey Stick.”
Here is the abstract from the paper1:
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.
There are several interesting and disturbing things about this study. First, it appears that the Urban Heat Island Effect does not explain the Hockey Stick. This is very disappointing because I was really hoping that Global Warming was not for real, or at least, not as bad as I had thought it might be. No such luck. Second, to the extent that this study may have had “Anti-Warmist” biases, and that in general, the scientists would have benefited career-wise by overthrowing the orthodoxy (that’s always a good science move these days, gets you all sorts of grants and awards …. nobody ever got the Nobel for reproving the proved) they still came up with a pro-Warmist conclusion. This has been happening for some time now … Anthropogenic Global Warming Denialists have been trying to disprove Global Warming and instead accidentally either prove it or show how bad they are at doing science, or just come up with some remark like “Oh, so if it’s real, that’s OK we just move the cities” and so on. Third, I am shocked … SHOCKED! … that there is not only no Urban Heat Island Effect, but that over recent years, the effect has been REVERSED from what we expect.
This is disturbing because, for instance, right now I’m at the cabin by the lake, and it is distinctly cooler than it is in the city. I am now forced to pursue other explanations for this observation. Let’s see … perhaps this is because I’m at a higher altitude, higher latitude, and next to a big wet lake. Perhaps. Perhaps not. But until these questions are answered with definitive data collected and analyzed by the Petroleum Industry, Imma say the Jury is Still Out. On the lake-side venue being cooler than the city. The part about Global Warming … well, I think the Jury has been Back from deliberations for years now. This latest paper could be seen as the last holdout, but it’s not even that. At most, it is the last nail in the coffin of a long dead argument.
1This abstract is from a pre-publication version of the paper and may not be exactly the same as the final abstract.
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