Cities and Global Warming

OK, I lied.  I have one more post I want to make on global warming now that Steve McIntyre's site is back up.  I suspect I tend to bury the lede in my warming posts, because I try to be really careful to set up the conclusion in a fact-based way.  However, for this post, I will try a different approach.  Steven McIntyre has reshuffled the data in a study on urbanization and temperature that is relied on by the last IPCC report to get this chart for US Temperature data.

Conclusion?  For this particular set of US temperature data, all the 20th century warming was observed in urban areas, and none was observed in rural areas less affected by urban heat islands, asphalt, cars, air conditioning, etc.

If it can be generalized, this is an amazing conclusion -- it would imply that the sum of US measured warming over the last century could be almost 100% attributed to urban heat islands (a different and more localized effect than CO2 greenhouse gas warming).  Perhaps more importantly, outside of the US nearly all of the historical temperature measurement is in urban areas -- no one has 100 year temperature records for the Chinese countryside.  However much this effect might be over-stating US temperature increases, it would probably be even more pronounced in measurements in other parts of the word.

OK, so how did he get this chart?  Did he cherry-pick the data?  First, a bit of background.

The 2003 Peterson study on urban effects on temperature was adopted as a key study for the last IPCC climate report.  In that report, Peterson concluded:

Contrary to generally accepted wisdom, no statistically significant
impact of urbanization could be found in annual temperatures.

This study (which runs counter to both common sense and the preponderance of past studies) was latched onto by the IPCC to allow them to ignore urban heat island effects on historical temperatures and claim that most all past warming in the last half-century was due to CO2.  Peterson's methodology was to take a list of several hundred US temperature stations (how he picked these is unclear, they are a mix of USHCN and non-USHCN sites) and divide them between "urban" and "rural" using various inputs, including satellite photos of night lights.  Then he compared the temperature changes over the last century for the two groups, and declared them substantially identical.

However, McIntyre found a number of problems with his analysis.  First, looking at Peterson's data set, he saw that the raw temperature measurement did show an urbanization effect of about 0.7C over the last century, a very large number.  It turns out that Peterson never showed these raw numbers in his study, only the numbers after he applied layers of "corrections" to them, many of which appear to McIntyre to be statistically dubious.  I discussed the weakness of this whole "adjustment" issue here.

Further, though, McIntyre found obviously rural sites lurking in the urban data, and vice versa, such that Peterson was really comparing a mixed bag with a mixed bag.  For example, Snoqualmie Falls showed as urban -- I have been to Snoqualmie Falls several times, and while it is fairly close to Seattle, it is not urban.  So McIntyre did a simple sort.  He took from Peterson's urban data set only large cities, which he defined as having a major league sports franchise  (yes, a bit arbitrary, but not bad).  He then compared this narrower urban data set from Peterson against Peterson's rural set and got the chart above.  The chart is entirely from Peterson's data set, with no cherry-picking except to clean up the urban list.

Postscript:  Please don't get carried away.  Satellite measurement of the troposphere, which are fairly immune to these urbanization effects, show the world has been warming, though far less than the amount shown in surface temperature databases.

Update: To reinforce the point about global sites, Brazil apparently only has six (6) sites in the worldwide database.  That is about 1/200 of the number of sites in the continental US, which has about the same land area.  And of those six, McIntyre compares urban vs. rural sites.  Guess what he finds?  And, as a follow up from the postscript, while satellites show the Northern Hemisphere is warming, it shows that the Southern Hemisphere is not.


  1. Laurence Sheldon:

    I wish. I really, really truly wish we (on all sides of this discussion) could take a time out and sort out the words being used.

    Here is my cut at it.

    Global warming: Since the end of the last deep "ice age" the globe has been getting warmer. Get over it. It is an axiom. Is getting warmer and will continue to do so until it stops doing so.

    Green house gases: To the extent that their sources are "un-natural" (what ever that turns out to mean), are components of atmospheric contamination or pollution.

    Pollution: Bad. Very bad. We should take positive steps to reduce it by finding better ways of doing what we want to do.

    What we want to do. Good. Very good. Especially the parts about raising standards of living, improving health and comforts, and freeing people from any of several forms of bondage.

  2. jsalvati:

    Wow. As a global warming agnostic, I find this pretty convincing. I will have to read all his work, but it looks like I will be changing my position to 'nominal CAW skeptic.'

  3. dearieme:

    This all just gets sillier and sillier. These Global Warming people - do they just have low scientific IQs, are they terminally careless, or are they liars?

  4. jt:

    I've lived in Boston ever since the 1960s, and I've seen noticeable warming during that time (e.g., the Charles River used to freeze solid in the winter, and now is mostly open water year round). But it dawned on me the other day that the warming I've seen is more than the fraction of a degree that we're supposed to have had from global warming during this period. A more likely explanation, I suspect, is that Boston (like most growing urban areas) now throws off a *lot* more BTUs in the winter from heating new buildings and homes, more cars, etc. In fact, virtually all of the fuel that comes into the Boston metro area--oil, gas, electricity--ends up escaping into the local environment as heat. I don't know how you'd calculate this, but maybe some of the warming phenomenon isn't the result of CO2 acting as a greenhouse gas--instead, we might be seeing an uptick in *direct* heating from the fuel we're burning so lavishly.

  5. Adam:

    jt, its been a while since I've had any classes in it but I beleive thats what thermodynamics says. Conservation of energy, or enthalpy or entropy or something along those lines.

  6. Knucklehead:


    A few years back (roughly 12 or 14 so I don't have the data at my fingertips) my daughter, then in early middle-school, needed to do a project that tied some sort of "science" with some other aspect of life. What she somehow arrived at (probably from a family dinner-table discussion) was checking Dear Old Dad's claims that, "when I was a kid we were always ice-skating on the frozen pond and sledding in the snow all winter long". There just wasn't all that much snow in NJ when mine were young. What she decided on was to check my recollections against data.

    She put a great deal of effort into her research. Among other things she contacted the US weather service or whatever they are called and had them send her data for the 50's through 90's. As it turned out, the '60s were an unusually cold decade and yes, Dad did a ton of ice-skating and sledding and snowball fighting when he was a kid. Much of the data was for the Northeast. It was the same throughout the region.

    Weather changes. Some decades/centuries/millenia are warmer/colder that others. During the revolution the Delaware River was clogged with ice. Nobody's seen that in quite some time. If you could live long enough you could be the farm that at some point in the future people will be moaning and groaning about how darned cold it is and how the Delaware, or the Charles NEVER used to freeze.

  7. Sharpshooter:

    Does anyone recall the hysteria about glaciers in Yellowstone Park a couple years ago? Seems pictures of the area from the 1880's were vastly different from those same areas today, setting off the usual shreeking from the usual suspects.

    Thing is, someone dug out pictures from the early 1900's of the same glacial areas, showing the glaciers had already retreated significantly by about 1910-1915.

    Of course, the "usual suspects" (media included) did not recant a single scream of alarm.

    The biggest problem I have with AGW is that the hysterics by the alamrists are, well, hysterical.

  8. Isaac Crawford:

    What I'm wondering is why the chart shows that the cities were so cold in relation to rural areas in the early 1900's. What's that all about?


  9. Jody:

    Issac: Steve normalized each line to that line's average temperature as averaged over a few decades (same decades for both, but I don't recall which ones - it's in Steve's post). What's plotted is the deviation from that average which reveals trends.

    So what the plots show is that urban 1900 temperatures were 2 C cooler than urban 1980 temperatures while rural 1900 temperatures were virtually unchanged over that period. This implies that (at least in the US) warming has been almost entirely an urban phenomenon which argues for urban heat island effects (asphalt, waste heat) being the dominant cause of warming. If CO2 (or the sun or any other global phenomenon) had been the primary driver, then both rural and urban areas should've seen similar increases over similar time scales.

  10. TCO:

    It's a very small subsection of the US data, so I don't know that it shows you that all heating has happened in urban areas. Also, hard to know if it is cherry picked or not. Did Steve try different cuts until he found one that emphasized the story?

  11. al fin:

    Now Climate Audit looks at Brazil and finds that for the entire country there are only 6 surface stations in GHCN!!!! For the whole country of Brasil!

    The temperature data for the US may be poor, but for most of the rest of the world it appears to be absolutely abysmal!!!

    No, TCO you professional troll, Steve did not cherry pick his numbers. But you never miss a chance to insinuate dishonesty on Steve's part. What a weanie.

  12. TCO:

    I'm not a professional troll. I just do such a butt-outstanding amateur job that you think I am. And I don't recall you. What is your other name or do you hide like a little pussy?

    On topic, there is a VERY GOOD point that people are not noting or thinking about, about how STeve has confounded regional differences with the rural/urban comparison. Take a minute and think about it. Read the CA post. Stop. Think. ks is the guy to read. Think. Read. Consider. Slow down...

  13. TCO:

    Check out the Tucson Detectives thread over at CA. Steve draws linear trend lines through two different samples over two different time periods. (IOW confounding a comparison of two time periods with two populations). I'm in shock, just butt-shock. That Steve refuses to fix that (being dishonest) or that he doesn't see the flaw (being stupid).

  14. TCO:

    The airport photo is in error also, as well as being poorly stated analysis (no definite statement of hypothesis). See here for more detail.

    It's not that this is some huge issue. But leaving it up there is dishonest and stubborn.

  15. TCO:

    Steve has finally corrected his earlier comments on the airport station. Rather gracelessly.