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Does Urban Heat Island effect exaggerate global warming trends?

What the science says...

Select a level... Basic Intermediate

Urban and rural regions show the same warming trend.

Climate Myth...

It's Urban Heat Island effect

A paper by Ross McKitrick, an economics professor at the University of Guelph, and Patrick Michaels, an environmental studies professor at the University of Virginia, concludes that half of the global warming trend from 1980 to 2002 is caused by Urban Heat Island. (McKitrick & Michaels)

The Urban Heat Island Effect (UHI) is a phenomenon whereby the concentration of structures and waste heat from human activity (most notably air conditioners and internal combustion engines) results in a slightly warmer envelope of air over urbanised areas when compared to surrounding rural areas. It has been suggested that UHI has significantly influenced temperature records over the 20th century with rapid growth of urban environments.

Scientists have been very careful to ensure that UHI is not influencing the temperature trends. To address this concern, they have compared the data from remote stations (sites that are nowhere near human activity) to more urban sites. Likewise, investigators have also looked at sites across rural and urban China, which has experienced rapid growth in urbanisation over the past 30 years and is therefore very likely to show UHI. The difference between ideal rural sites compared to urban sites in temperature trends has been very small:

Figure 1. Annual average temperature anomalies. Jones et al (dotted green and brown) is a dataset of 42 rural and 42 urban sites. Li et al (solid green and brown) is an adjusted dataset of 42 rural and 40 urban sites. Li (blue) is a non-adjusted set of 728 stations, urban and rural. CRUTEM3v (red) is a land-only data set (Brohan et al., 2006). This plot uses the 1954–83 base period.

Another way to explore the UHI would be to look at where the majority of warming has occurred across the globe. The UHI should match where most people live. However, if you look at the 2006 global temperature anomaly (figure 2.), you find that the greatest difference in temperatures for the long term averages where across Russia, Alaska, far north Canada and Greenland and not where major urbanisation has occurred.

Figure 2. Using source data from NASA/GISS, this illustration shows the amount of change in global surface temperatures in 2006 from 1885.

The Urban Heat Effect has no significant influence on the record of global temperature trends.

Basic rebuttal written by mothincarnate

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 5 July 2015 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Further reading

  • The Modern Temperature Trend (by Spencer Weart). An in-depth history of surface temperature measurements since the late 1800's. If you find this lengthy article fascinating, you're a complete nerd (raises hand sheepishly).
  • The Power of Large Numbers (July 2007 by Tamino). Explores how we can discern with precision temperature trends with the statistical power of large numbers.

Further viewing


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Comments 51 to 53 out of 53:

  1. koyaanisqatsi I infer from the lack of the term 'adjusted' (figure 1 - basic) that Jones et al is comparing unadjusted rural and urban temperature stations and finding little difference. "[NASA GISS] found in most cases, urban warming was small and fell within uncertainty ranges. Surprisingly, 42% of city trends are cooler relative to their country surroundings..." So it reads as if A) UHIE is small and B) UHIE is corrected for, although though the aggregate of the corrections makes a negligible difference to the temperature record anyway.
  2. Koyaanisqatsi, When uncorrected data is compared there is no statistical difference between rural and urban sites. GISS has pointed out that they only lower urban measurements. Detailed comparisons show that some urban sites are lower than nearby rural sites. These data are never raised. That means that the UHI corrections result in a small lowering of the estimated temperature trend from the actual trend. The difference is not statistically significant. The estimated trend is left too low to be conservative. UHI is constantly raised by fake skeptics to muddy the waters. In reality, it is a very small effect that does not alter measured temperature trends.
  3. Tristan and Michael, Thanks for your responses. I'll have to think some about them. And I should probably read the Hansen 2001 process description. "UHI is constantly raised by fake skeptics to muddy the waters." Don't I know it. I am debating with a "skeptic" and I've tried to explain several times why UHI effects are not the cause of Climate Change or GW. His climate change research is targeted to Web sites that support his denialism. I've provided links here many time on many issues, but the guy never learns--he just recycles the same old idiocies. Drives me crazy. But UHI effects would hardly let people off the CO2 hook since UHI effects are largely due to automobiles and electric devices powered by CO2 emitters.
  4. A response to arationofreason, who posted this question:

    "An increase in temperature over the last 70 years may be due to urbanizaton around the increasingly urban sites"

    Inconveniently, the Koch Industries-funded BEST team has debunked this tired, trite meme.  While urban areas are undoubtedly warmer than surrounding rural areas, this has had little to no impact on warming trends.

    "The Urban Heat Island effect is real. Berkeley’s analysis focused on the question of whether this effect biases the global land average. Our UHI paper analyzing this indicates that the urban heat island effect on our global estimate of land temperatures is indistinguishable from zero."


    "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 is consistent with no urban heating effect over the period 1950 to 2010"


    "The simple take-away is that while UHI and other urban-correlated biases are real (and can have a big effect), current methods of detecting and correcting localized breakpoints are generally effective in removing that bias. Blog claims that UHI explains any substantial fraction of the recent warming in the US are just not supported by the data."

    You are welcome to try again, but with actual evidence in lieu of your preferred empty assertions.


  5. Is it true also that met stations which measure temperatures in rural areas have significantly reduced over the last decade all over the world? if so wouldnt this signify that the results are distorted?

    Also the amount of rainfall across Australia increased from 1900 to 2000, however the rain may have fallen across different areas of land that expected by farmers. Does global warming take into account that rain doesnt always fall in the same location. 

    Has anyone setup a way to directly measure the reduction of the ozone layer from gases that can reach that high in the atmosphere and also directly measure how much heat from the sun the layer actually allows through. If direct measurement is accomplished and demonstrated this might be considered scientific evidence, before that time its always going to be a myth or an assumption to a portion of humanity. Kind of like a Ponzi scheme to many people I think. I have an interest in all of this as Im a studying university student

  6. Recommended supplemetal reading:

    Urban Heat Islands Don't Explain Climate Change - Here's The Bigger Problem by Marshall Shepherd, Science, Forbes, May 6, 2019

    The lead paragraphs of Sheperd's essay:

    A recent flurry of activity on social media last week centered around a new study published in the Journal of Applied Meteorology and Climatology. According to the abstract, it found that "temperature observations (in an experiment with four observation sites) were warmest for the site closest to the built environment." This finding is not "News." We have known about the Urban Heat Island (UHI) effect for many decades, and I have previously described it in Forbes.

    I suppose the novel caution in this new paper is that urban "creep" is possible at some temperature stations used for overall climate change assessment like the U.S. Climate Reference Network. My colleague Dr. Roger Pielke Sr. has a deep body of work on land changes and climate impacts so I suspect he is very pleased to see studies like this as am I. However, this essay is written as an antidote to wild claims spouting the "cliche" or "zombie theory" that climate warming is caused by urban heat bias. Not only is that flawed, there is a greater danger that many have overlooked.

    One of my favorite climate scientists to follow on social media is Zeke Hausfather. A 2013 study published in Geophysical Research Letters by Hausfather and colleagues examined the urban bias on the U.S. Historical Climate Reference Network (USHCN). According to the NOAA website,

    The U.S. Historical Climatology Network (USHCN) data are used to quantify national- and regional-scale temperature changes in the contiguous United States (CONUS). The USHCN is a designated subset of the NOAA Cooperative Observer Program (COOP) Network with sites selected according to their spatial coverage, record length, data completeness, and historical stability.

  7. Yes.  I admit...I am a "Heat Islander" until all sources of science has been observered this effect has no bearing in cultural concern.   This said, I have often wondered about how a geologist would respond to this subject as I have been taught that surface models have a tremendous impact on global climate.   Then a friend of mine shared this link to me that shows that there is a noteabel absense from this field of science among the GWA board (LINK).   If this wasn't enough to anger me, University of Maryland University College made a determination that the geology course was no longer transferrable as a "life science" towards my degree (this was during the time when the focus started shifting on the perils of greenhouse gasses in the media).  Anyhow, if anyone is interested, I will gladly explane the global relief map codes that apparently used to be used by climatologists.  I hope I can still find a copy of one online to illustrate.


    [DB]  That is not a credible source for science information, as this Note details at length.

  8. Absolutely right, Darinscoop, if not more so.  The alternating currents of the urbanised regions do produce a concentrated electromagnetic induction effect, warming the temperature sensors in the local weather stations.  The previous explanation of UHI from "exhaust-heat and sun-warmed pavement" is a shabby falsehood put forward by a conspiracy of contrarians, who are receiving grants & other funding from Big Oil.

    The world is actually cooling and the sea level is falling.  Even the contrarians are hoaxing us.

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