Las Vegas Temperatures: The Plot Thickens

June 27th, 2014 by Roy W. Spencer, Ph. D.

This is my third post on Las Vegas temperatures. Not that I wanted to do 3 posts…but I keep running into “issues” regarding the thermometer data available from NCDC.

In yesterday’s post I thought I was providing the “official” USHCN temperatures for Las Vegas, as downloaded from an NCDC web page.

But there are 2 new problems:

1) that NCDC page seems to be buggy…it gives exactly the same data for maximum, minimum, and average temperatures.

2) Las Vegas is not a USHCN station anyway.

The point of my original post was to examine Las Vegas temperatures as perceived by the public. We all know it’s hot there in July, and as my two previous posts indicated, the McCarran Airport temperatures exhibit a strong urban heat island (UHI) warming signal over time (much more warming at night than during the day). The same is probably true of the North Las Vegas airport, which is where the NWS currently reports temperatures from.

So, if a record high temperature is reported on any given day in Las Vegas, it will likely be for these unadjusted, UHI-influenced temperatures…not from NCDC-adjusted USHCN temperatures (which don’t include these stations anyway).

Since there is a strong UHI warming effect there, such record setting temperatures are pretty meaningless in a climate context. With an increasing UHI effect, we expect the frequency of temperature records broken to increase over time. (Without a spurious UHI warming effect, and no global warming, we would expect the frequency of broken records to decrease over time…with 2 years of data, there’s a 50% chance of breaking a high temperature record, with 3 years, a 33% chance, etc.)

So, the bottom line remains the same. The UHI effect has probably hopelessly corrupted urban stations like Las Vegas (as Anthony Watts also concluded in his post from yesterday). Inferring anything about global warming from new temperature records set at these stations is impossible.

32 Responses to “Las Vegas Temperatures: The Plot Thickens”

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  1. Don B says:

    Even with UHI, the record temperatures for 35 US states were set before 1940.

  2. Ted says:

    Your own satellite-based temperature dataset shows a continual warming trend. Is it affected by the urban heat island effect?

  3. geran says:

    Perhaps they chose Las Vegas to taunt the Warmists/Lukewarmists.

  4. Ted says:

    @O H Dahlsveen

    Obviously this year’s (or last year’s) average temperature is lower than for 1998. It was also colder in 1985 than in 1980. So what? Looking at the longer trend line most people who aren’t trying to cherry pick a comparison date would say the graph shows increasing temperatures over the entire period of record.

    I would also note that the 13-month trend line in 2010 was just as high as in 1998, and that the temperatures between those years were much higher than before 1998.

    In any case, your post is irrelevant to my question for Dr Spencer, which remains unanswered.

    • JohnKl says:

      Hi Ted,

      You wrote:

      “Looking at the longer trend line most people who arenít trying to cherry pick a comparison date would say the graph shows increasing temperatures over the entire period of record.”

      If by longer trend line you mean the entire UAH dataset (1979-2014) this appears to be true. However, the UAH dataset presented doesn’t comprise RAW data, but ADJUSTED DATA. Wikipedia at one point listed 10 adjustments made to the UAH temp dataset, including a 1 deg centigrade temp increase in 1998 due to orbital decay believe it or not. Since the orbital decay can have only worsened since that time it would be interesting to know how much further the data has been adjusted as a result of orbital decay since then, not to mention other WARMING adjustments not publicized. If you consider the fact that the Earth still faces ICE AGE conditions and likely continues a warming trend and continually increasing sea level rise present for CENTURIES, what does anyone really know about the relative impact of GHG’s?

      Have a great day!

    • For the entire data set, over 30 years, the trend is about 1.7C per century. For the last of the data set, it’s closer to a zero trend. There is a positive trend, but it’s not much.

    • Fonzarelli says:

      As much as it pains me to say it, I have to agree with Appel on this one. (It hurt a little David but I can take it…) The last five years of the UAH data set were warmer than the previous five which were warmer than the previous five, etc. This holds true going all the way back to ’79. I would think that constitutes “a continual warming trend” (as articulated by Ted)…

      • Appel is a rather extreme fellow. He will slice and dice a data set until it says something he wants it to say (if he can). Over 30 years, the first half of the data set showed warming. The second half shows close to zero warming. If the second half of the data set showed stronger warming than the first half, guys like Appel would be screaming about it from the roof tops. The fact that it doesn’t and he tries not to mention it, speak volumes too.

  5. Richard Harris says:

    The latest peer-reviewed article on this subject seemed to lay the UHI question largely to rest, though admitting the effect is real (Hausfather et al 2013). “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. (summary by one of the authors).

    Has anyone looked at US cities that have lost significant population. It is easy to say that you can explain a temperature increase by a correlative increase in population but if you look at major cities with significant population increase they do not show a negative UHI do they?

    • KuhnKat says:

      Richard Harris, the Horsefeather paper makes one glaring assumption, that rural stations will NOT have a noticeable UHI.

      Tell me, have you or anyone else done the observational work to prove they do not?!?!?!

      When there is a network where the stations could not possibly be affected by UHI compared to rural/urban stations we MIGHT get some real answers.

      In the meantime there have been a few foreign papers that HAVE found UHI not to mention the NASA direct observations of the difference in temps between cities and their surrounding areas. As the city had to warm as it grew, compared to the area with no urbanization, there absolutely HAS TO BE UHI!!! As Moshpup and others like to say, it is BASIC PHYSICS!!!

    • Tom in St. Johns says:

      As a city’s population declines the infrastructure that the larger population built generally still exists (think Detroit). So the heat sinks remain when the people are gone so I don’t believe this to be a valid method.

    • Hausfather’s paper seems to be the exception to the rule. Most of the papers I’ve read on UHI have found a strong effect that biases trends to varying degrees. But unfortunately that’s the way climate activism works… Cite a paper that agrees with what you already believe, ignore the dozen others that don’t. (sigh)

  6. I just checked out NCDC data for average maximum temperature in Las Vegas in past Julys, at this site:

    I chose 1937 as the start year, because IIRC, Anthony Watts mentioned the reported warming trend starting then. What I found is that most of the warming trend can be explained by a sudden maximum temperature jump in 2002.

  7. Christopher Game says:

    May I ask a question that may be a little off track right here. What is the precise structure of the 13-month centered average?

    Presumably the thirteen months are chosen to remove the annual seasonal cycle effects. Good idea.

    Likely it is a thirteen-month (not the obvious 12-month) average because 13 is an odd number and this way the center falls right on (not between two) one point on the graph. Good idea, but with perhaps a slight wrinkle.

    One obvious structure would be that the thirteen calendar months’ data are equally weighted. But, represented twice, the extreme annual month then gets twice the weight of the rest. Perhaps a slightly curious way to go? No particular worry, but just a slight feeling of unease.

    I am wondering if another possibility might have been used, equal weighting for all the months except the first and last, which would have half a weight each? Then every annual month would have one and the same weighting.

  8. GW says:

    The JIG is UP ! Steve Goddard was right all along; Watts, Hausfather and others were wrong ! 40% of the USHCN stations are bogus, fabricated “E” data ! Watts just owned up to it in his latest post !

    Goddard’s investigation, now accepted as true, shows mostly rural stations have been infilled with warmer data from the nearest urban station creating a phony warming trend !

  9. CC Squid says:

    NCDC has dead stations that are reporting data that isn’t real.
    “All of that added up to a big heap of confirmation bias, I was so used to Goddard being wrong, I expected it again, but this time Steve Goddard was right and my confirmation bias prevented me from seeing that there was in fact a real issue in the data and that NCDC has dead stations that are reporting data that isnít real: mea culpa.”

  10. James Strom says:

    Much of the UHI effect comes from roads, parking lots, and structures. When a city loses population, most of these features remain. You’ll see abandoned lots and malls if you visit Chicago or Detroit, and unless these cities acquire a large infusion of funds they will not regreen their idle infrastructure.

  11. darrylb says:

    Have you heard the news—– 1936 holds the record again!!
    2012 is (officially) no longer the heat record holder, according to WUWT

  12. ej says:

    Summarized from today’s Las Vegas Review-Journal…

    Las Vegas July
    record temperatures
    by decade

    highs lows
    2010+ 4 0
    2000+ 7 0
    1990+ 2 0
    1980+ 2 2
    1970+ 4 0
    1960+ 0 0
    1950+ 2 2
    1940+ 7 18
    1930+ 3 9

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  14. bit chilly says:

    from a layperson point of view there is an issue to be addressed by DR Roy Sencer in relation to how well the satellite temperature trend matches that of the surface temperature trend in light of the issues surrounding the methods used to create the surface temperature record.

  15. Wyo Skeptic says:

    Just a note for the record. The Climate at a Glance Website is wonky. For individual sites, it gives the same data for max temp, avg temp, and min temp. For state wide data it gives data that avg is offset a set amount above min or a set amount below max.

    • wyoskeptic says:

      I didn’t describe it very well. When looking at statewide data, the numbers for average lie exactly midpoint between min and max.

      Never seen any normal data do that before.

  16. LASJayhawk says:

    Just a note on the Vegas data. The records for Jan 1, 1937 through Dec 17, 1948 were taken at Western express field (Now Nellis AFB) 1877′ above sea level. Then the station moved to Alamo field (now McCarren Int’l airport) elevation 2162′ The new location is 14 miles SW of the original.

    The instruments at McCarren Airport are the official station of record.

    Also IIRC North Las Vegas airport is a coop station. There is a coop station at the NWS office about 3 miles SW of McCarren but the data from it does not show up on line as far as I can tell.

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