Urban Bias on Surface Temperature Record

A lot of folks have started to analyze the surface temperature record for urban biases.  This site has linked a number of past analyses, and I’ve done some first-hand analysis of local surface temperature stations and measurements of the Phoenix urban heat island.  My hypothesis is that as much as half of the historic warming signal of 0.7C or so in the surface temperature record is actually growing urban heat islands biasing measurement stations.

Edward Long took a selection of US measurement points from the NCDC master list and chose 48 rural and 48 urban locations (one for each of the lower-48 states).  While I would like to see a test to ensure no cherry-picking went on, his results are pretty telling:

Station Set
oC/Century, 11-Year Average Based on the Use of
Raw Data
Adjusted Data
Rural (48)
Urban (48)
Rural + Urban (96)

More at Anthony Watt, who has this chart from the study:

The Reference Frame has more analysis as well.

If this data is representative of the whole data set, we see two phenomena that should not be news to readers of this site:

  • Inclusion of biased urban data points may be contributing as much as 5/6 of the warming signal in the test period
  • The homogenization and adjustment process, which is supposed to statistically correct for biases, seems to be correcting the wrong way, increasing clean sites to matched biased ones rather than vice versa  (something I discussed years ago here)

The homogenization process has always bothered me.  It is probably the best we can do if we don’t know which of two conflicting measurements are likely to be biased, but it makes no sense in this case, as we have a fair amount of confidence the rural location is likely better than the urban.

Let’s say you had two compasses to help you find north, but the compasses are reading incorrectly.  After some investigation, you find that one of the compasses is located next to a strong magnet, which you have good reason to believe is strongly biasing that compass’s readings.  In response, would you

  1. Average the results of the two compasses and use this mean to guide you, or
  2. Ignore the output of the poorly sited compass and rely solely on the other unbiased compass?

Most of us would quite rationally choose #2.

Most climate data bases go with approach #1.

Let’s remind everyone why this matters:  We are not going to eliminate past warming.  The Earth was at one of its coldest periods in 5000 years through about 1800 and it has gotten warmer since.   The reason it matter is twofold:

  • The main argument for anthropogenic causes of warming is that the rise of late (particularly 1978 – 1998)  has been so steep and swift that it couldn’t be anything else.  This was always an absurd argument, because we have at least two periods in the last 150 years prior to most of our fossil fuel combustion where temperature rises were as fast and steep as 1978-1998.  But if temperatures did not rise as much as we thought, this argument is further gutted.
  • High sensitivity climate models have always had trouble back-casting history.  Models that predict 5C of warming with a doubling have a difficult time replicating past warming of 0.6C for 40% of a doubling.  If the 0.6C is really 0.3C, then someone might actually raise their hand and observe that the emperor has not clothes – ie, that based on history, high sensitivity models make no sense.
  • Charlie A

    In your choices of what to do when you have a poorly sited compass and a well sited one, you forget option #3: adjust the well sited one to conform to the reading of the poorly sited one.

    This option, of course, is only used in those cases where for some reason you prefer the reading of the poorly sited compass. /sarcasm off

  • hunter (the real one)

    “While I would like to see a test to ensure no cherry-picking went on, his results are pretty telling”

    By this, you mean “I don’t understand what they’ve done or why, but I do like their conclusions”

    “The main argument for anthropogenic causes of warming is that the rise of late (particularly 1978 – 1998) has been so steep and swift that it couldn’t be anything else. This was always an absurd argument, because we have at least two periods in the last 150 years prior to most of our fossil fuel combustion where temperature rises were as fast and steep as 1978-1998. But if temperatures did not rise as much as we thought, this argument is further gutted.”

    No, that is not the main argument. What would make you think that it was? Just how little actual reading about climate science have you actually done?

    “High sensitivity climate models have always had trouble back-casting history.”

    They have no trouble at all. You cannot, in fact, explain any past climate change unless the climate sensitivity is close to 3°C, which I guess is what you mean by high. You do not have the intelligence to see that this point contradicts your previous point. No fast change in climate is possible unless climate sensitivity is high, and you happily point out several instances of fast change, too dopy to understand the implications.

    When will you learn to keep your pathetic ignorance to yourself?

  • hunter (the sane one)

    >sigh< Perhaps it is the cutbacks at my little copycat's clinic that lead to her/his/its under medicated rants?

  • Wally

    @ Hunter (the idiotic one)

    He by no means says (or implies) that he doesn’t understand what is being done or why, and anyone that has those thoughts is an idiot. He rightly critisizes Watt’s analysis for not being fully inclusive, but with 48 sample in each group, we should have enough of a sample size to at least consider the conclusions reasonable, or suggestive. Meaning it would be a great idea to pull every sample we could find and do the same thing and see if the same trend is found. So, this isn’t proof absolute that all (or 5/6 of it) the warming is coming from the heat island effect, but it does suggest that. And at the same time the AGW argument hasn’t proven their case either. Their whole argument relies on an argument from ignorance. That basically being, “we’ve seen X warming over the last 30 year and can’t explain it, so it must be man made.” It should be clear to any rational human being that this kind of argument is completely worthless. You can’t claim, I know that A, B and C aren’t causing Z, so it must be Y that is causing Z, because you also can’t prove that it is or is not D-X.

    So, in the end, it doesn’t matter if Watt’s argument is perfect, he isn’t trying to prove anything one way or the other. Its the AGW crowd that has the burden of proof because they are the one’s making the claim. Skeptics are simply not convinced by the evidence presented by the AGW crowd. So, we don’t have to actually prove there is no AGW, we just have to show you can’t prove that there is AGW. Those are two very different things.

  • Kelly

    One reason to be glad you doubt Climate Change: The Dutch – simply too dim-witted and self-absorbed to realize what fools they are making of themselves on this..
    Absurd images from recent National Dutch Climate Change PR-Event “Beat the Heat” here:

    Meet the winners of the Climate Science Quiz – showered with prizes for ‘correct’ answers to questions like “What would the temperature of the earth be without the influence of G/house gases??”..
    No prizes for realistic answers unfortunately..

  • denis

    Take a look at a recent (and separate) comparison by Dr. Roy Spencer, between satellite data and surface data. His conclusions appear to be similar – that UHI seems to be added into the surface temperatures rather than being excluded.


  • Arn Riewe

    One of my favorites is the “science fair” project of son & father. While they are not “climate scientists” someone please tell me what’s wrong with the UHI analysis:


  • kuhnkat


    Dr. Edward R. Long, ex NASA, performed the study, not Watts.

  • mbabbitt

    Please don’t feed the troll.

  • ADiff

    Backward projections clearly don’t match historic conditions. An extended period (13+ years, and counting) that have been entirely divergent from what AGW models predict, make it clear not only the model, but the data itself, should be re-considered. And yet AGW’s chief spokesmen seem fixated on responding to policy disputants and ruminating on conspiracy theories (Mann’s most recent NPR interview is an excellent example) while ignoring substantive challenges to their models, theory and the integrity of underlying data sets. Could it be they just can’t answer these challenges? Their responses raise some disturbing questions. Mann said he would address science, but all he talked about was policy and political opinion! Does a desire for particular policy objectives have complete precedence over any other consideration for he and other AGW advocates at this point?

    Does Mann really think it’s productive of any objectively beneficial end to base a discussion on the premise that refusal to agree with his perspective is proof one’s evil and that everyone who questions him is a member of some vast organized conspiracy funded by the oil companies? Can he have so totally lost touch with reality to actually believe that?

    It’s a sign of believers in conspiracy theories that they take a few fragmentary truths and spin them into a seamless fantasy explaining everything in a way completely exonerating their own particular preferences and view of reality. Michael Mann sure sounded like he was well down that road in the NPR interview I heard this weekend….

    Is that locale a recent arrival for him, or has he actually already been camping there for some time?

  • anon

    I’m pretty sure I’ve seen a better non-cherry-picked data set — IIRC they simply removed all sites w/ a lat/long within XX miles of a the home city of any NBA or NFL team.

  • wcthomps

    This is an embarrassing misrepresentation of science. Mr. Meyer would do well to stick to economics. Moreover, the mere notion that he is capable of commenting on such science based upon his background in dynamical systems and control (which I very much doubt, as engineers obtain only limited experience in the fields, especially in terms of the complexity required for computational climatology) is personally insulting to me (as someone who actually does work in those fields.

  • ADiff

    So Wcthomps’ argument amounts to “because I say so”. How convincing.

  • hunter

    You would look much more convincing if you would show just where and how this is so embarrassing.
    It seems to Mr. Meyer is showing fairly clearly that at heart AGW is exhibiting the classic sign of crap science: making huge conclusions based on evidence that is barely outside the margin of error and variability.

  • Pogo

    To “wcthomps” and his idea of “misrepresentaion of science”, may I draw your attention to the following?

    “Physics is the only real science. The rest are just stamp collecting.”

    Ernest Rutherford

  • David

    Can I just say that I feel that Wally’s February 28 comment pretty well encapsulates what we are trying to say all along..!