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Media Extrapolating A Trend From A Single Data Point: 2018 Heatwave Edition

September 5, 2018

By Paul Homewood


This is a relevant post from Coyote Blog:



This article in something called Inside Climate News seems to be typical of many I have seen this year:  Because we have had much attention in the media on heat waves this year, there must be an upward trend in heat waves and that is a warning signal that man-made global warming is destroying the planet.  Typical of these articles are a couple of features

  1. Declaration of a trend without any actual trend data, but just a single data point of events this year
  2. Unstated implication that there must be a trend because the author can’t remember another year when heat wave stories were so prevalent in the media
  3. Unproven link to man-made global warming, because I guess both involve warmth.

I have no idea if well-publicized heat waves this year are a harbinger of an accelerating global warming trend.  But since we are discussing "trends" it struck me as useful to actually liven up the discussion with some actual trend data, ie data for more than one summer.  There is a real danger to extrapolating trends from volume of media coverage, as I discussed here.  If you don’t want to click through, I have a funny story in the postscript.

First, our most reliable temperature trend data does not really show a spike in temperatures this summer.  Remember, a heat wave that covered the entire US would only affect 6% of the world’s landmass and <2% of the world’s total area (source).  You can easily see the trend upwards several tenths of a degree over the last 40 years, but it is impossible to see much unique about the last 3 months of summer.

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Second, there really is no substantial upward trend in US heat wave index (from right off the EPA’s web site, as are all of the following charts.  Look at the source for yourself to make sure I am not playing games).  Note that all of the following charts are through 2016 and do NOT include the recent summer but are pretty meaningful none-the-less.

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Third, in most of the country, there is actually a downward trend rather than upward trend in extreme heat days.

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Pretty much everyone agrees, skeptics included, that the world and the US has warmed.  So why are extreme heat days down in many locations, and certain down from the 1930’s?  This defies our intuition.  The explanation is in part due to a feature of global warming that is seldom explained well by the media, that much of the warming we see and as predicted in climate models is in the night.  We are seeing some increase in hot daytime highs, but really not at an unprecedented level over the last century.  BUT, we see MUCH more of a trend in hot daily lows, which basically means warming evenings.

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I spoke at Amherst College a while back and here was their temperature trends, broken up between daily highs and nighttime lows.  All of Amherst’s temperature trend since 1950 has not been in increased daytime highs but higher nighttime lows.  This is a pattern you see repeated over and over at nearly every temperature station.

This is why I consider media reports of heat waves, at least of the scope we have seen to date, absolutely irrelevant to "proving" the world is warming.


Postscript: Here is the story everyone should keep in mind when extrapolating from media coverage volume to underlying trends:

let’s take a step back to 2001 and the "Summer of the Shark." The media hysteria began in early July, when a young boy was bitten by a shark on a beach in Florida. Subsequent attacks received breathless media coverage, up to and including near-nightly footage from TV helicopters of swimming sharks. Until the 9/11 attacks, sharks were the third biggest story of the year as measured by the time dedicated to it on the three major broadcast networks’ news shows.

Through this coverage, Americans were left with a strong impression that something unusual was happening — that an unprecedented number of shark attacks were occurring in that year, and the media dedicated endless coverage to speculation by various "experts" as to the cause of this sharp increase in attacks.

Except there was one problem — there was no sharp increase in attacks. In the year 2001, five people died in 76 shark attacks. However, just a year earlier, 12 people had died in 85 attacks. The data showed that 2001 actually was a down year for shark attacks.


Update:  I am not really an active participant in the climate scene any more, particularly when positions hardened and it was impossible to really have an interesting discussion any more.  The implicit plea in this post goes beyond climate — if you are claiming a trend, show me the trend data.  I can be convinced.  There is clear trend data that temperatures are increasing so I believe there is an upward trend in temperatures.  Show me the same for droughts or heat waves or hurricanes and I will believe the trend about those as well, but so often the actual data never matches the arm-waving in these media sources.

I have just one comment.

Have a look again at the NOAA map below, and ask yourself why NOAA use 1948 as the starting point, thus missing out the much warmer 1920s and 30s?


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  1. Geoff Sherrington permalink
    September 5, 2018 10:28 am

    Neat work, thank you, Paul.

    Continuing with data, for Australia I did this work for heatwaves:

    Click to access are_heatwaves_hotter.pdf

    For USA, Tony Heller made this graph recently about record setting. In this case it is for maximum temperatures, the number of records claimed or present each year.. For more discussion see,

    No matter which way I slice and dice heatwave data, like you I find it hard to show that scare talk is supported by evidence. BTW, when I ran the Aussie heatwave data past our BOM, they said they could not contemplate such material unless it was in a peer-reviewed publication. There is no benefit in a scientific publication whose required skills are little more than addition and subtraction of simple numbers, so I declined. Geoff.

  2. The Informed Consumer permalink
    September 5, 2018 10:29 am

    BBC arm waving yesterday.

    Reporting that this ‘summer’ was the hottest ever recorded in England, by a very tiny amount, but presented as evidence of Global Warming.

    Except that if the rest of the UK was included it didn’t achieve the record set by 1976, and a few other years, which they did mention, but with no fanfare.

    It seems regional events are now being presented as evidence of AGW by the BBC, in spite of it being a global phenomenon.

    • The Informed Consumer permalink
      September 5, 2018 10:31 am

      BTW, the above should be HotScot.

      No idea why WordPress erratically defaults to Informed Consumer.

    • MrGrimNasty permalink
      September 5, 2018 11:15 am

      As pointed out widely, England was not the warmest in the CET, the best data, but even that is probably lacking required downward adjustment in latter years. Summer 2018 was 0.5C cooler than 1976.

      • dave permalink
        September 5, 2018 3:52 pm

        Whether our weather is unusually hot, is something ordinary people will always decide for themselves. Propaganda concerning this particular sphere of expertise of Englishmen is toothless.

  3. September 5, 2018 12:53 pm

    One data point has NEVER been part of the Scientific Method. Not even Michael Mann’s 24 trees out of a data base of 250 and certainly not his colleagues predictions based on 3 trees qualify as anything close to scientific.

    • Gerry, England permalink
      September 5, 2018 1:42 pm

      ‘ask yourself why NOAA use 1948 as the starting point, thus missing out the much warmer 1920s and 30s’

      Hmm, the words Cherry and Picking come to mind.

    • Gerry, England permalink
      September 5, 2018 1:46 pm

      In the book that examined Mann’s hookey stick, they asked the reasonable question as to why no further tree ring samples had been taken to continue the sequence. The answer is probably the same reason Mann grafted the instrument record onto the end of the graph. If used they would show cooling, not because it did but because trees grow mainly in response to moisture not heat.

      • MrGrimNasty permalink
        September 5, 2018 7:25 pm

        I recall that there have been several tree ring studies, one very recent, from trees preserved in cold waters, Norway or Finland or such like, that have shown that the Roman and Medieval warm periods were warmer than today.

    • September 7, 2018 1:38 pm

      Dendrochronology is not a technique which should be used to say anything about CO2. There is just too much “noise.” It is useful to date things. You can tell about moisture and temperature over time with the size of annual growth rings. But with all of the factors which come into play for growth rings in a single tree, a small number is very useless–(unless you are dating something.

      For example, Mesa Verde, the Indian cliff dwellings in southern Colorado, were dated by overlapping corings taken from logs within the structures overlapped with others until reaching current trees. It also showed many years of drought which accounted for the abandonment of Mesa Verde.

      If you want to recreate CO2 and other gases you need to use ice cores and they abound. Also seafloor cores which show microfauna, etc. can be used.

  4. Jonathan Bensted permalink
    September 7, 2018 6:20 am

    I am not a climate scientist, but this graphical representation of NASA GISTEMP data seems fairly unequivocal to me. Interested to hear the counter-arguments..

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