Repost: Putting the "Urban Heat Islands" issue to bed

Preface on reposting policy I and others have been discussing concerns about the ephemerality of blogging. Given that blogs are a searchable database, there’s no real reason why people should look only at the current pages. But in my experience, comment threads tend to die off after a few days. However, Aaron Oakley has just put in a comment on a post from December 2002, and this gives me a chance to announce my new policy. If anyone comments on a post that has been archived (more than 10 days) I will do my best to repost it and thereby reopen the debate.

Preface to the repost Now here’s the reposted piece. I think the article quoted in the paper refutes Aaron in advance, but just to be clear I’ll restate my point. I agree with Aaron that urban heat islands are real even in small towns (in fact, I’m glad to see Aaron endorsing the reality of human-induced climate change). I also agree that estimates of climate change need to be checked using only rural stations. But, as the cited article says this has already been done, and it makes no significant difference to estimates of global warming. Note that Aaron himself recommended this article.

Reposted article begins
Bizarre Science points to this study confirming the IPCC contention that Urban Heat Islands, while a real phenomenon, are not important in assessing estimates of the rate of global warming C.J.G. (Jon) Morris of the School of Earth Sciences, The University of Melbourne, reports

Whilst climatologists now think that the warming in the temperature record from some small urban areas is partly the result of the UHI, this is not evidence that Australia’s climate has remained unchanged rather than warmed over the past 100 years. Average minimum temperatures from many stations over most of Australia have shown an increase of between 0.1 deg C and 0.3 deg C per decade since 1951. Whilst some temperature records from small towns do not represent the large scale climate, it is unlikely to have any major impact upon our estimates of temperature warming over Australia. This is because there are numerious other weather stations located in remote areas such as lighthouses and regions far removed from urban areas that still indicate a warming temperature trend.

Thanks for this useful link!

Update While I’m at it, I also appreciate this post, in which BS reader Reader George Bogg points out that, given the number of points in Alan McCallum’s scatterplot, the trend he finds is almost certainly statistically significant (thereby resolving the main remaining point of dispute). However, Bogg misses the point that this is a panel data set, consisting of observations from many different stations over time. An analysis taking this into account would yield a much stronger correlation. Of course, as Bogg points out the fact that the world is getting hotter doesn’t prove anything about the causes. But at least agreement on the facts is a start.

22 thoughts on “Repost: Putting the "Urban Heat Islands" issue to bed

  1. John Quiggin, eager to dismiss the urban heat island effect, will be dissapointed by the following paper:

    Urban Heat Island Features of Southeast Australian Towns’

    Australian Meteorological Magazine (v.50, 2001, 1-13)

    The authors concluded –

    “these results imply that climatological stations in large cities should preferably be excluded from studies into long-term climate change, and those in small towns should be located away from the town centres.”

  2. ??? Me endorsing the reality of human induced climate change???

    That’s drawing a long bow.

    It is exasperating to have to explain this again but here is my position:

    I think that the world warmed a lot between the end of the little ice age and about 1940, cooled until 1975 and has has had a slight rebound since then.

    The vast bulk of this change has been natural, and can be linked to causes such as variation in solar intensity.

    Therefore, there has been global warming AS DISTINCT FROM man made global warming.

    I AM NOT endorsing the reality of human-induced climate change. Any such change is most likely to be much smaller than the limit of error in estimates of tempetature change.

  3. The UHI is a LOCAL effect. When talking about climate change, we invariably do so in the context of GLOBAL CLIMATE, not local effects!!!

  4. Who is “WE” in this context, Aaron? I’ve seen a great many studies of human-induced changes in local microclimates. They didn’t seem constrained by your “invariable” rule.

    And, obviously, local changes add up to global change. If you accept one, you can’t rule out the other.

  5. Aaron’s statement “[t]he vast bulk of this change has been natural, and can be linked to causes such as variation in solar intensity”, could be said to true if one discounted the century. In the later part of 20th Century, considerable warming occurred, when the solar intensity predicts a drop in temperature.

    As far as I know, no scientific study can do decent job of explaining temperature variability over a thousand year time-scale without including significant contributions from solar, volcanic and greenhouse gas effects.

  6. Your’e playing games again, John. By “we” I mean you and I, when debating GLOBAL climate change. For example, I distinctly recall you worrying about the great barrier reef being affected by GLOBAL warming. This is hardly an issue if the effect is restricted to Melbourne and Sydney etc.

    “Local changes” do not neccessarily add up to “global changes”. In the case of local changes, we are simply producing more heat. Also, tarmac on the roads absorbs more solar energy. If you are worried about this LOCAL kind of warming, then why not advocate a strategy which will ameliorate this, instead of one aimed at curbing CO2 emissions> After all, it is not CO2 that is at the heart of the UHI.

    Ken, Solar activity reached a local minimum in 1986 but has been climbing since then. This would appear to correlate with the small increases in temperature since then. FYI see this article by Dr Theodor Landscheidt:

  7. Not only was there a local minima in 1986, there was also one around 1996. These come about from the solar cycle. Interestingly, neither of these two recent minima are associated with a particular cold period. Very surprising if one assumes that solar variations are dominant. Not very surprising, if one takes the mainstream scientific view.

    I thought that I said a scientific study. And definitely not something endorsed by John Daly, I have no desire to go searching through his references to see what has been distorted.

    However, since non-peer reviewed evidence seems to be the name of the game, I’ll throw in , which tracks temperatures and proxy solar data from the 1860’s to just about the end of the 20th century. The correlation between solar and temperature variability gets considerably worse after the 1970’s.

    Or if we want to use a scientific study, Crowley (Causes of Climate Change Over the Past 1000 Years, 2000, Science, 270) found that “[t]he bulk of the 20th-century warming is consistent with that predicted GHG increases”.

  8. Actually the article in question was written by Dr Theodor Landscheidt. If you want to smear someone, smear him instead.

  9. Crowleys thesis was based on the contention that the current temperatures were unusually high, in historic (~1000 yr) terms.

    Clearly this is not the case. The earth was much warmer than today in the preceding interglacial periods for which good temperature proxy data are availiable. These were at times when CO2 never got above 290 ppm

    PS, Ken, if you want to smear Dr Landscheidt personally, I can provide you with the contact details.

  10. Aaron, reread my post. I never claimed that the article was written by John Daly. I don’t trust it, for exactly the same reasons as too why I don’t trust articles posted on the ICR’s website. As for smearing John Daly, it isn’t a smear if it’s true.

    The evidence that the MWP was hotter than late 20th century temperatures is spotty at best. The authors of the report are better at writing press releases than they are at constructing a solid case. However, should their contention be true, it means that Crowley has underestimated the warming influence of GHGs.

    If the MWP and Little Ice Age were more pronounced than the data which Crowley used indicates, then the pre-20th century climate variability is more correlated with solar variability than Crowley determined. This means that the effect of GHG variation must play a significantly greater role to account for the considerable deviations between solar and climate variations in the latter part of the 20th century.

  11. The Landscheidt article isn’t up to date. For example he refers to Lassen/Friis-Christensen (1991), but their result is based on the fact that they combined different data. (The first part are 55year-averages, the part after 1970 isn’t filtered at all.) Lassen himself has corrected this spurious result. (Thejll/Lassen 2000) But John Daly simply ignores the correction.

    The CR-hypothesis is refuted:

  12. Hi John,
    I have response to your post at:
    [ ]

    As a fence-sitting sceptic the big question to me is still did we humans do it?
    If I can drive thru Heywood [pop. 1100] and measure UW then surely scientists can too.

    From *where* comes the notion that historical UW cannot be estimated?
    We estimate everything else.
    Astronomers do light curves of stars using one data point taken periodically.
    In principle we could infer that the earth was warming in the long-term from just one location!

    Anyway, I have probably said enough to cop some stick already.

  13. I realize I’m coming into this late, but can anyone point out where in the aforementioned study JUST HOW FAR OUT FROM CITIES THE PAPER SAID THE UHI EXTENDS?

    Didn’t think so. The paper discussed magnitude, not likely extent and whether the UHI affects 25% of the land, 2.5% or .0025%


  14. Ken, Its a smear if you dont back up your insults with evidence.

    The MWP spotty? There is both historical and physical evidence for this from all over the globe. Wine grapes in England, Greenland actually green… etc etc etc etc …or has this dissapeared down your orwellian memory hole?

  15. Aaron, it’s ironic that you use the phrase “orwellian memory hole”, as John Daly uses that exact phrase as he tells a big fat juicy lie. While critiquing a paper by Michael Mann, he states “Mann completely redrew the history, turning the Medieval Warm Period and Little Ice Age into non-events, consigned to a kind of Orwellian `memory hole'”. ( This is grossly untrue. Mann in his paper notes the existence of both the MWP and the Little Ice Age (so much that climate change skeptics such as Soon use Mann’s paper as evidence for the existence of both the MWP and Little Ice Age). I alerted Daly to this error (as well as several others) several months ago, and he simply ignored that part of my email, and his website hasn’t been corrected. Given that he rewrites Mann paper to say the exact opposite of what it does (and then bases his whole critique on this deception), then after this is pointed out to him, makes no effort to change his critique or refute my claims, I would seriously doubt his honesty.

    On to your second point, I said that the evidence for the MWP being warmer than late 20th century temperatures was spotty, not that the evidence for the existence of the MWP was spotty. Given that England grows grapes nowadays, and the areas of Greenland that the Vikings settled are still green, these provide absolutely no evidence for the MWP being warmer than recent temperatures.

    Finally, nice graph. Now find a scientific paper that can reconstruct recent temperature trends without significant amounts of GHG effects. Interestingly, subsequent to the creation of your graph, the effects of solar variability on climate was reviewed (Lean, J and Rind, D. Climate forcing by changing solar radiation, Journal of Climate. 1998. 11(12) 3069) and found that solar variability can explain the majority of temperature variability upto 1800, but drops off significantly after that (from the 1970’s onwards it can account for approx. 1/3 of the temperature variability) – results fully consistent with global warming.

  16. In my opinion, it’s safe to assume that there is no easily definable cause or causes for global warming. The effect, which is undeniable, is undoubtedly due to a combination or conglomeration of multiple natural and artificially induced factors. I’ve even heard it expressed as a totally natural occurence which the planet goes through every so often because of fluctuating output from the Sun. Now, while I personally don’t subscribe to this theory as a sole causitive factor, there may well be some measure of input to the overall impact of global warming. How much input is virtually unassessible.

    Therefore, and again this is only my opinion, no one single theory is right and no one single theory is wrong. All must have elements of possibility, indeed probability to them, unless categorically proven false.

  17. Niall, your correct. There have been attempts correlating various variables (such as solar output, greenhouse gases etc) to observed temperatures.

    The models which have the best fit to reality, have significant amounts of volcanic, solar and greenhouse gas effects. They also show greenhouse gases starting to dominate in the latter part of the 20th century. However, the fits of stimulated to observed temperatures are far from perfect, indicating that there are other factors playing a big role in temperature variability.

  18. Interstingly, John Christy claimed in recent tesimony to the senat that “temperature swings have been common in the past 1000 years and that temperatures warmer than today’s were common in 50-year periods about 1000 years ago.”

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