(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: The apparent rise of global average temperatures is actually an illusion due to the urbanization of land around weather stations, the Urban Heat Island effect.
Answer: Urban Heat Island Effect has been examined quite thoroughly (PDF) and found to have a negligible effect on temperature trends. Real Climate has a detailed discussion of this here. What's more, NASA GISS takes explicit steps in their analysis to remove any such spurious signal by normalizing urban station data trends to the surrounding rural stations. It is a real phenomenon, but it is one climate scientists are well aware of and have taken any required steps to remove its influence from the raw data.
But heavy duty data analysis and statistical processing aside, a little common sense and a couple of pertinent images should put this idea to bed. Here is an image, taken from Astronomy Picture of the Day (a wonderful site, by the way), of the surface of the earth. It is a composite of hundreds of satellite images all taken at night. (The large version is well worth the download time!)
Aside from being very beautiful, it is a perfect indicator of urbanization on earth. As you can see, the greatest urbanization is over the continental United States, Europe, India, Japan, Eastern China, and generally coastal South America.
This next image was taken from NASA GISS. It is a global surface temperature anomaly map which shows warming (and infrequently, cooling) by region.
Look at North America, look at Europe, at Asia, Australia, Africa and the Poles and compare them to the urbanization in the image from APOD. There is quite simply no way to discern any correlation whatsoever between urbanization and warming. If the UHI effect were the cause of warming in the globally averaged record, we would see it in this map.
The claim that global warming is an artifact of the Urban Heat Island Effect is simply an artifact of the Urban Myth Effect.
Addendum: Wikipedia has a very good article on this subject. Among all the interesting details it mentions a few papers that directly discuss efforts to identify and quantify UHI influences on the global temperature trend including this one (PDF), which would be a good one to cite:
A 2003 paper ("Assessment of urban versus rural in situ surface temperatures in the contiguous United States: No difference found"; J climate; Peterson; 2003) indicates that the effects of the urban heat island may have been overstated, finding that "Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures." This was done by using satellite-based night-light detection of urban areas, and more thorough homogenisation of the time series (with corrections, for example, for the tendency of surrounding rural stations to be slightly higher, and thus cooler, than urban areas). As the paper says, if its conclusion is accepted, then it is necessary to "unravel the mystery of how a global temperature time series created partly from urban in situ stations could show no contamination from urban warming." The main conclusion is that micro- and local-scale impacts dominate the meso-scale impact of the urban heat island: many sections of towns may be warmer than rural sites, but meteorological observations are likely to be made in park "cool islands."
If necessary, be sure to refer to all the other ways we know the global warming trend is not an artifact of anything. It is real.
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Comments
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wacki Posted 8:26 am
28 Oct 2006
Just so your readers know, this myth was put forth 'in part' by the economist Ross McKitrick among many others. Heh, I'm not done with his profile page either so no link. :p
Just curious, did you come up with the graph comparison by yourself or did somebody else point it out to you?
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wacki Posted 8:28 am
28 Oct 2006
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Coby Beck Posted 1:50 pm
28 Oct 2006
Thanks for the feedback! :)
Invent a clever saying, and your name will live forever!
-- Anonymous
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TokyoTom Posted 6:45 pm
29 Oct 2006
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Jumbo Posted 3:22 pm
12 Feb 2007
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Micawber Posted 10:13 am
17 Jun 2007
Why is there no edit? And don't say because there's a preview. Really, why?
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carboncat Posted 10:06 am
03 Sep 2007
" 40 clusters were compared using data from 1989 to 1991. Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures."
um, he looked within a narrow range of 2 years - in US-only data - and didn't find a significant effect. That's not exactly a refutation.
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lfstevens Posted 7:56 am
05 Mar 2008
He goes over the ground carefully and reaches a pretty big conclusion - that the heat island effect is NOT properly compensated for.
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barry schwarz Posted 4:46 pm
15 Jun 2008
Watts and his team have collected a good number of sites they think are of good standard. At the time of this post [transferred from illconsidered blogspot - posted late February 2008], they're about a third of the way through the project.
They have plotted the US temperature profile using only the sites they think sound, and have compared with the profile as given by the US Climatology Network (http://cdiac.ornl.gov/epubs/ndp/ushcn/newushcn.html), which is used by GISSTEMP and HADCRU.
So far, the results provide a very good fit.
http://yaleclimatemediaforum.org/features/1007_surfacetem ...
That article links to climateaudit, a well-known skeptical site run by Stephen McIntyre, which has been working on the data from the 'good' weather stations as determined by Watts' team. In the thread doing the math on the preferred data stations, this is the post (below) where one of the skeptics, John V, compares the surfacestations.org data with USCHN.
http://www.climateaudit.org/?p=2124#comment-147569
Even the skeptics are getting the same result as the mainstream. If anyone is sincerely interested in this subject, the surfacestations/climateaudit project now spans three threads (the post above is from the second one, which is 300 posts long), and it will be interesting to see the results when they complete their project. [If the results have been updated, I would be interested to know]
As a side note, I consider the discussion going on in this climateaudit thread to be the very best example of the skeptical community putting their money where their mouthes are. It is a substantive, polite investigation, and while they have begun with their conclusion (not very scientific), they are genuine in their efforts. When so much skepticism (and advocacy, for that matter), is couched in ignorance and vitriol, this project champions the best of the skeptical community. Let it be a standard-setter for all sincere discussion on climate change.
And, the US temperature profile looks almost exactly the same when all the urban data is excluded, which is one thing that is done to test for UHI.
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Plumb Bob Posted 5:48 am
25 Jul 2008
This says nothing whatsoever about urban heat island effects; it says that whatever global trend we're watching, it affects the northern hemisphere more. In fact, what it says about the recent warming is precisely what you folks say about the Medieval Warm Period and the Little Ice Age: that the warming is a regional phenomenon, not a global one.
But it doesn't say a blessed thing about urban heat island effects. Your charts don't put any objections to bed, contrary to your confident claim.
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Paleocon Posted 3:43 pm
17 Sep 2008
How does any of this prove that man is causing a significant impact on the climate?
What percentage of climate change is attributable to man versus nature?
What is the perfect climate?
When did it exists on Earth?
How will we stabilize the planet at this perfect climate?
Is it OK to counter-act the natural rate of change?
Do only people in San Diego, CA get to vote on "best climate", or do sub-Saharan Africans get to vote? Maybe they would like glaciers covering most of North America?
Just don't take any more of my family's money until you can answer THESE questions. Spend as much of your own as you like.
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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GreyFlcn Posted 3:51 pm
17 Sep 2008
_
You effectively got 2 atmospheric layers that make up the near entirety of our atmosphere.
You got sunlight coming into the earth, and heat reflecting back out into space.
If "something" in the lower layer, were blocking heat from getting to the upper layer; Then what you'd expect to see is that the lower layer would get hotter while the upper layer would get colder.
_
Well guess what,
That's exactly what's been happening.
http://greyfalcon.net/forcing2.png
-David Ahlport
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Paleocon Posted 4:01 pm
17 Sep 2008
What will we do to stop it?
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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Pangolin Posted 5:53 pm
17 Sep 2008
Sorry, just channeling the deniers.
They can't understand that they're wrong when presented with facts because facts didn't lead them to their original position. Like the GOP, religious-whackjob Anthony Watts they arrived at the conclusion that supported their tribes behavior and then sought to prop it up.
This study, written up in the Washington Post, shows that conservatives actually get stupider when confronted with factual information that refutes a pre-established belief.
Now why did you have to go and do that to them?
Put the Carbon Back
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Paleocon Posted 4:34 am
18 Sep 2008
All women who refuse to date you are NOT lesbians, and all people who disagree with you are not "stoopit".
Liberals have lost the ability to debate intelligently. I suppose it is the result of a popular culture that embraces one side of the argument so whole-heartedly. It breeds a certain laziness.
What do you propose we do to stabilize the climate and end the natural background level of change?
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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GreyFlcn Posted 8:54 am
18 Sep 2008
So when we want to talk about "Natural" variables.
1. For very large 15,000+ year time scales, what we're dealing with primarily is changes in the earth's orbit. This however is far too slow to be relevant on the 100 to 1 year time scale.
http://greyfalcon.net/milankovitch
2. Natural factors alone do not explain the warming trend we've seen in the past 4 decades.
http://greyfalcon.net/forcing4.png
http://greyfalcon.net/lean2005.png
3. The El Nino Cycle however does explain 1998 and 2008.
http://greyfalcon.net/rsstemps.png
http://greyfalcon.net/elnino
http://greyfalcon.net/lanina
4. And for kicks, it'd be nice to point out that US Mainland temperatures, and Global temperatures are different things. (1934 was not the hottest year "globally")
http://greyfalcon.net/ustemps.png
http://greyfalcon.net/globaltemps.png
________
As for propositions, how about we attempt to get back down to 380ppm CO2 in the atmosphere. (i.e. The highest we've ever been in the past million years) Both by reducing emissions, and by enhancing carbon sinks.
http://greyfalcon.net/carbon2
For the US, this would probably be best served by putting a point-of-wholesale surcharge on Coal, Oil, and Natural Gas by CO2 content.
And then using that money for grants to purchase low carbon end-use technologies, and grants for large scale carbon sequestration projects.
(Or frankly, I don't really care what gets done with the money. It could also be used to buy a lifetime supply of hookers and scotch for Republican Senators)
http://i-r-squared.blogspot.com/2008/08/taxes-versus-subs ...
http://en.wikipedia.org/wiki/Pigovian_tax
With of course an overall goal towards low cost/carbon electricity, and electric transportation.
Promising technologies for those are:
* EGS Geothermal
http://www.youtube.com/watch?v=O6r_3AgI49Y
* Concentrating Solar Thermal with Molten Liquid Salt Heat Storage
http://greyfalcon.net/solarthermal
http://greyfalcon.net/solarthermal2
http://greyfalcon.net/ausra
* PHEVs
http://greyfalcon.net/plugins7
* Nano Lithium Batteries
http://greyfalcon.net/quickcharge3.png
* Nano Ultracapacitors
http://www.autobloggreen.com/2007/03/10/nanotech-strikes- ...
_
(Nuclear power of course, isn't low cost electricity. If anything, it's about the most subsidized form of electricity on the planet, and virtually every other nation that does it operates their programs as Federal Monopolies.)
http://greyfalcon.net/nuclear
-David Ahlport
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Pangolin Posted 4:52 pm
18 Sep 2008
Global Warming in the last century is a FACT. Multiple sources of data and analysis from ice cores to tree rings to migration patterns have established this beyond doubt.
AGW has been established to the level of scientific certainty that allows us to put people on jumbo jets and wave happily as they fly away. Sure sometimes all the parts don't quite fit but for the vast majority of uses the theory flies.
The people who deny AGW can safely be classified along with the flat earthers, chemtrail nuts and those who believe the planet is only 6,000 years old and built by a sky fairy who likes to do rock sculptures in the shape of sharks teeth.
So quote Anthony Watts and don't be surprised when people rank you with the people who knock on doors Saturday mornings and hand out religious material. My bad for taking advantage.
Put the Carbon Back
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Paleocon Posted 3:11 pm
20 Sep 2008
What other scientific debates have you "settled" that are in the same league as climate change?
Sustainable Nuclear Fusion would be a weekend project for folks as smart as you, having figured out climate and all.
AGW Fundamentalism is the "dark energy" of climate science. It takes an IQ "above your pay grade" to understand how absurd it is to say the scientific debate is over.
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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Paleocon Posted 3:22 pm
20 Sep 2008
Since the debate is over, you must have a link to the data set that would disprove the AGW/ CO2 hypothesis.
I will provide you with the hypothesis refutation data for any current scientific theory you like.
Do you understand what that means? Science is not a tool for pimping a political agenda.
This is what we get when schools are run by the government, I suppose.
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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mreinbold Posted 3:57 pm
20 Sep 2008
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GreyFlcn Posted 4:07 pm
20 Sep 2008
Well then, can you please provide me with a reason why the stratosphere is cooling, in sync with the troposphere warming?
-David Ahlport
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Pangolin Posted 5:21 pm
20 Sep 2008
Collect all you want. It's free. Energy storage and distribution is a different problem.
Put the Carbon Back
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Paleocon Posted 9:01 am
22 Sep 2008
I guess that is "consensus". Everyone agrees with you that is allowed to post.
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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Paleocon Posted 9:06 am
22 Sep 2008
Improving PV efficiency is arguably the best place to spend research dollars.
But aren't you concerned that if you asked people to support a Nuclear Reactor 8 minutes away from where they live that they would say NIMBY?
LOL.
"...a 90 percent chance that the US has contributed .2 degrees F of temperature increase in the last 50 years..." The IPCC Consensus in perspective
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Pangolin Posted 10:10 am
22 Sep 2008
Put the Carbon Back
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