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.
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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
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I cannot find the original article or any reference. Googling "Influence of urban heating on the global temperature land average using rural sites identified from MODIS classifications" or a part of the absract only shows this post.
Try here:
http://berkeleyearth.org/resources.php
which page lists (and links to) four papers submitted for peer review.
Perhaps I'm misreading, but if I read the abstract correctly, the claim does not imply that there is no urban heat island effect. It implies that the urban heat island effect is mostly independent of global warming, perhaps becoming just a bit less marked as global warming increases.
You're right: it would have been much better news had they found that current climate models incorrectly accounted for urban heat islands.
I wonder if any of the 'felt' effects of warmth in Urban environments is related to the amount of heat being pumped out of buildings and cars (not to mention engine temps) and into the surroundings.
It wouldn't change anything from the global warming or urban island effect.
I guess what I'm really wondering is how much is concrete absorption and how much is caused by AC units.
As an aside, I grew up in SE Texas, with several of the largest refineries in the US, we had a big urban island effect. One local weatherman called it the "Chem Dome". You could watch small lines of thunderstorms break up as they got to us and then reform on the other side.
Let me be clear: There are hot cities. There are cities where there is probably a strong heat island effect. What is the case, however, is that temperature measurements used to estimate global temperature are not significantly affected by this effect, and ironically there is a negative, but still statistically not significant effect, in the latest years (which are also the most warm).
And yes, absorption of heat implies later release, so the overall effects may be zeroed out but on a minute by minute basis there can be observable effects, like storms parting around cities, etc.
I should also add this: Some of the effects we see where weakly defined weather fronts, etc. , act differently as they pass over cities can have another explanation. For instance, Minneapolis/St Paul have different topography than surrounding areas; Boston is in a very 'special' place, topographically, as is Washington DC. Lots of cities are sitting on bits of landscape that are different from surrounding areas, and in some cases, those differences may be related to the reason the city is in that particular location.
Since climate science is using anomaly rather than absolute temps it doesn't matter how hot a city is. What matters is how much the city's anomaly changes over time and what direction that change is. The denialists are claiming that cities are warming faster than the rural areas and unduly affecting the overall average anomaly.
@ Gary (#6),
Actually the septics don't generally think that cities are warming faster. They think that cities, and suburbs have spread. So some or all of the observed warming is coming from the conversion of rural stations to urban.
It was clear before this paper that the septics were wrong, and its clear now that they won't change their minds.
OgreMkV
I don't remember the "Chem Dome" but I do remember the "Rush Hour Rinse" caused by the sea breeze hitting the heat island and carrying all the moisture high into the air. The pollution seeded the cloud. Some summers it would rain like clockwork almost every afternoon. We must have watched different weathermen.
OK, I can see how heat island bias could distort measurements of global average temperature, but what about the polar ice caps? If it's melting things must be hotter. I don't really see how potential bias in how we measure the global average is going to overturn that basic fact.
Bacopa, you're assuming denialists need more than a shred of hope to hold onto their wishful delusions.
Blueshift: It is not clear at all. The paper just came out today at noon Pacific time. Give them at least until tomorrow morning to change their minds!
I'd be glad to wager with you on their doing so to any significant degree, Greg. :) I'll take the "no they won't" side of the bet.
Well, judging by the numerous emails I've gotten so far, you may be right, sadly.
Greg,
Re the negative effect in recent decades - my hypothesis (unsupported by any analysis, mind you) is that the cities were already pretty warm, due to the urban heat island effect, and that any effect from global warming is having less impact as a result - as I'm sure you know, warm areas lose their heat faster than cooler areas - radiative heat transfer goes with the 4th power of temperature, I think. So for a given imbalance in the heat flux (such as that due to the greenhouse effect), the warmer areas wont warm up as much as the cooler areas.
Just running some basic calcs - for each square meter, a 1K change in temp results in an increase in radiative heat loss of 5.17 watts at 283K (10C, or 50F), but 5.45 watts at 288K (15C / 59F). Not a huge difference, but enough that given X watts of extra heat from the enhanced greenhouse effect, cooler areas will warm slightly more than warmer areas, such as cities.
I choose neither. ;-)
I prefer "Climate Contrarian" for opponents of the 97% climatological consensus on Human Induced Rapid Global Overheating (HIRGO) and HIRGO for AGW (Anthropogenic Global Warming) instead.
Bacopa @8
Yeah, I remember the 4 O'clock rains too. That was in the 80s, maybe early 90s.
Greg Bostwick kind of started the Chem Dome in the late 90s.
As far as my questions, I've done some research and it does appear that heat pumps have a small, but noticeable effect on the temperatures in cities.
This post suffers from mixed-metaphoritis. The hockey stick was a metaphor for the untrended pre-industrial temperature record. The UHI metaphor pertains to the effect of local/regional socio-economic trends on the corresponding temperature trend. As this study does not regress local socio-economic variables against the temperature record, it cannot provide any insight into the UHI effect.
Comparing Rural vs. Urban records is perhaps the worst way of estimating UHI. Rural records are more sensitive than urban ones to a specific socio-economic change. Prof. McKitrick, however, has peer-reviewed publications utilizing the necessary approach. His findings are that about a third of the global trend can be explained by local socio-economic impacts. One can argue with his specific regression model and whether the findings are spurious, but IMHO this is the proper approach.
AG, UHI is not a metaphor. I think you are grabbing at straws. Your comment regarding rural vs. urban is another good example of grabbing at straws! Comparing Rural vs. Urban is the exactly correct way to compare ... (wait for it) ... Rural vs. Urban!
Please stop grabbing at straws, or you might end up with the straw that breaks the camel's back. I'll give you mixed metaphores!
AG, UHI is not a metaphor. I think you are grabbing at straws. Your comment regarding rural vs. urban is another good example of grabbing at straws! Comparing Rural vs. Urban is the exactly correct way to compare ... (wait for it) ... Rural vs. Urban!
Please stop grabbing at straws, or you might end up with the straw that breaks the camel's back. I'll give you mixed metaphores!
The UHI's biggest fan is brother Watts from Watts Up With That where he's spent a lot of time arguing that the placement of temperature equipment is biasing temperature readings in urban areas. He also believes that removing high altitude (colder) sensors from the overall average gives a biased reading.
What this shows is the man does not understand anomaly and how it is calculated.
Greg... nice strawman ;)
A wise teacher of mine once told me that 90% of arguments are caused over differing definitions. UHI, in the simplest of terms, is obviously just the temperature difference between an urban area and an adjacent rural area. I will agree that the temperature trends in urban and rural areas are similar, but that doesn't tell us anything about the impact of local socio-economic trends on local temperature trends. I like my refined definition of UHI better.
Ciao, AJ
AJ, my straw man must be lost in your fog. Please stay on topic.
Garry, "Watts" is going ballistic. You should see the emails he sends me about every 45 minutes.
@ ^ Greg Laden : Well, I guess you could post some of them for our amusement here - or would that be too mean?
Mean? Who cares about that! I'm not posting the denialist emails to me because they are all based on links they want me to read, and wouldn't make sense without the links. And I don't post their stinking links. But if anything really worth the read comes along, I'll post it!
It may be serendipity, but I read more than the first line of your blog because you blew the first line: Combustion, in of itself, has a de minimis affect on urban heating. (Google: "combustion urban temperature" first reference http://paos.colorado.edu/~englishj/UrbanWeather.htm -- more to it than just looking at H20, but looking at the energy flux you get the same answer). It got me curious as to what else might lurk there.
Anyhow, surprise, surprise, the paper lists Saul Perlmutter as a co-author. Yep, same guy who just won a free trip to Sweden.
Next time I see him, I'll have to kid him. Being a newly minted Nobel Prize winner and all, I guess he now has the right to pontificate on anything and everything. lol.
(For the record, Muller was, I think, Saul's thesis adviser. One of Saul's grunts must have a tie-in. Not related to anything Saul's been doing in the past two decades)
Remo, I don't think that web site makes much of an argument that combustion is not a factor. And, I list it as one of the factors that is considered relevant.
Greg old chap, I read your wonderful analysis and do you know what? I don't think you believe in what you wrote. This B.E.S.T thing smells worse than the con Manns hockey stick. Rats are diving into the water by the hundreds. The ship has a few minutes left at best. Jump off and find a different way.Get onto a lifeboat that isn't full of holes and rats and fight the cause with the truth and not lies.
RMK@26:
followed by:
Not the best judge of which is which are you, old sport?
"Rats are diving into the water by the hundreds."
Name some.
"This B.E.S.T thing smells worse than the con Manns hockey stick."
What items, in particular, are troublesome?
Remo, I went and read that page you referenced, and it only tries to estimate the impact of the water vapor produced by combustion, not the amount of heat. (btw, the argument made there for the water vapor impact is spurious anyway, and the author also does not know how contrails are formed.)