Does Anybody Really Know How Hot It Is?

Comparison of raw temperature data to the adjusted data for seven stations in New Zealand
(Figure 6.15 from the study being discussed)

Over the past few years, I have written about problems with the data related to global temperature measurements (see here and here). It is very difficult to get a handle on how the planet’s temperature has changed over the past century or so, because the only long-term data we have come from thermometers that are placed at various spots throughout the world. Since 1979, we have much more accurate global temperature data, which come from satellite measurements. However, those satellite measurements are not consistent with the thermometer measurements.

This is an important issue, because climate models (which make projections about future temperatures based on different emission scenarios) are “calibrated” against the known temperature data in an effort to make them more realistic. Since the satellite data have only been collected since 1979, they are rarely used. Instead, the longer temperature record (based on thermometers) is generally preferred. The two commonly-used thermometer records are GISS TEMP (maintained by NASA) and HadCrut4 (maintained by the University of East Anglia and the UK Met Office). Those two data sets are in good agreement with one another, but once again they do not agree with the satellite data.

Are these thermometer data reliable? Based on the PhD thesis of John D. McLean at James Cook University, the answer is “no.” He did what he claims is the first audit of the reliability of the Hadcrut4 data, and he has found 25 areas of concern. I will discuss only three. First, he finds many instances of anomalous data. One station in Colombia, for example, reports that the 1978 average monthly temperatures in April, June, and July were 81.5 oC, 83.4 oC, and 83.4 oC. In case you aren’t familiar with the Celsius temperature scale, that’s about 180 oF. Given that the highest temperature ever recorded on earth was 134 oF, it’s safe to say that the report from Colombia is simply wrong. He lists many other examples of anomalous data that cannot possibly be correct.

Second, he finds that for the vast majority of the record, the global coverage was incredibly poor. From 1850 to 1852, for example, there was only one land station (in Indonesia) and a few ships traveling a trade route that reported temperature data for the entire Southern Hemisphere. As time went on, coverage got better, but as he writes:

Even as a notional concept the global coverage has varied greatly over time, being less than 50% of the Earth’s surface for about one-third of the data record from 1850 to 2015 and only having been greater than 75% for only the last 60 years (since 1956). Even at the end of 2015 there was no coverage of 16.6% (i.e. 1/6th) of the Earth’s surface.

As a measure of global temperature, then, Hadcrut4 is only valuable for the last 60 years or so, at best.

Finally, what I see as the biggest problem he found is something that has also been seen in the GISS TEMP data as reported through the NOAA. In order to account for various changes that occur over time, temperature data are “adjusted” to make them more homogeneous. There is nothing wrong with doing that, but as you can see from the image at the top of the page, the adjustments tend to affect the earlier data more than the later data. In the example shown above (for seven stations from New Zealand) the effect is to make the past cooler relative to today. As far as I can tell, there is no justification for that. The author seems to agree:

There is no reasonable explanation of why earlier data should need a greater adjustment because temperature observations should have the least interference and distortion when the station commences operation at any given site.

In other words, the adjustments are supposed to take into account problems that develop after the station is operational, such as heat-trapping buildings being constructed near the station. Thus, adjustments should affect the recent data more than the past data, but this audit found the opposite. The problem, of course, is that only the adjusted data are used by climate scientists trying to understand global climate. So climate scientists are using data that overemphasize any warming that has happened over the past 150 years.

The author does more than simply list his many (justified) criticisms of the Hadcrut4 data set. In Section 8.7 of his thesis, he proposes a method to construct the best possible data set for global temperatures. I am not sure I am qualified to assess the value of his proposal, but based on what he has found in his audit, something must be done.

16 thoughts on “Does Anybody Really Know How Hot It Is?”

  1. I don’t understand the third problem. Aren’t adjustments always made after a station becomes operational? Regardless of how old those stations are? How does this differentiate between older and newer data?

    1. Yes, they are made after the station is operational. But the idea is the early years should be the closest to ideal, since the station is new and the spot has been chosen as a good one for measuring temperature. Thus, the raw data should be the closest to the real value when the station is newer. Consider, for example, the urban heat island effect, caused by the fact that roads and buildings heat up their surroundings. Stations are initially built away from civilization to reduce that effect. As time goes on, however, civilization approaches the stations. That makes the stations read hotter. If any systematic adjustments should be made, then, the later years should be cooled, not the early years.

  2. I was in a conversation about this a few years ago trying to explain this in general against someone who was adamant that the data has been consistently measured for a long time. This article gives me a reference for the future. Thanks!

    1. That’s not really a study, as there is no new science in it. I know the news report he references calls it a study, but the group that made it calls it a “special report.” You can see the entire report here. Once again, this report relies heavily on climate models which are tweaked based on thermometer-based temperature measurements, which the study I am discussing here demonstrates are not reliable. As climatologist Dr. Judith Curry says:

      I don’t see much in the way of new science or better ways of assessing uncertainty — same old, same old. Projections are based on the CMIP5 simulations. There are some more recent references cited in the ‘impacts’ chapter.

      She concludes with this:

      IMO, even with erroneous attribution of extreme weather/climate events and projections using climate models that are running too hot and not fit for purpose of projecting 21st century climate change, the IPCC still has not made a strong case for this massive investment to prevent 1.5C warming.

      1. so because you can ask a half backed question we should jsut keep releasing green house gasses and pretending it cna;t hurt? Meanwhile you rationalize ignoring studies that have been done,

        1. I am not sure how it is “half backed” to ask whether or not the temperatures that are used to tweak climate models like CMIP5 are accurate. Since those models are the basis of all the projections about future climate change, I would think that any scientist would want them to be accurate. Also, I am not sure why you think I am advocating that we should “jsut keep releasing green house gasses and pretending it cna;t hurt.” I don’t know anyone who believes that. However, as a scientist, I think we need to answer two very important questions:

          1) How much will the increased greenhouse gas content in the atmosphere hurt? So far, there is no good scientific answer for that question

          2) Are there any benefits to the increased greenhouse gases that might at least partially offset the amount they hurt? Since we don’t know the answer to (1), it is hard to answer this question.

          I am a big fan of using renewable energy where it is practical, and I am a strong supporter of investing in research and development that will make renewable energy more practical in more situations. However, until we can get reasonable answers to the two questions listed above, it is scientifically irresponsible to make sweeping policy changes that we know will have severe negative impacts.

    1. As usual, the media doesn’t do well reporting on scientific studies. The study they reference looked at one aspect of climate models (how the earth is sampled) and applied a correction to it which cooled off the model projections a bit. But even with their cooled-off models, there was still a discrepancy between the models and the data. Here is an article by climatologist Dr. Judith Curry. In this article, she talks about several studies, including the one referenced in the Guardian article you linked. Her conclusion is:

      Gridcell extreme frequencies in CMIP5 models do not overlap with observations. And satellite-measured temperature trends in the lower troposphere run below the CMIP5 rates in the same way that the HadCRUT4 surface data do, including in the tropics. The model-observational discrepancy is real, and needs to be taken into account especially when using models for policy guidance.

  3. “Since the satellite data have only been collected since 1979, they are rarely used. ”
    Is satellite data used from 1979 on? If not, why not, since it’s supposedly more accurate and complete? Thanks.

  4. I think a lot of this was mentioned in the book Climategate by Brian Sussman. He talked about how spotty the temperature station coverage was and how some of the stations are not properly controlled. One station at lake Tahoe had a trash burning barrel next to it for 20 years. Also for nondigital stations the people who record the temperatures frequently record at the wrong time of day to save time. There are stations inaccurate up to 2 degrees which are recalibrated only once every 2 years. Also that some stations represent tens of thousands of square miles which gives the data very poor resolution. Have you read any of the Climategate emails? The emails seems to imply that adjustments to the data intentionally depress historical temp recordings.

    1. I wrote an article about the emails shortly after they were released. What I got from them is that Dr. Mann didn’t like the fact that his temperature reconstruction showed declining temperatures in the more modern years, so he employed a “trick” to “hide the decline.”

      1. I’m the Climategate book the author mentions that the north polar ice cap had melted almost completely twice in the 20th century. Once in the 1930s and again in the late 1950s. Its hard to find any records of this online. Do you know anything about this? Because if it’s true retreat of arctic ice is completely normal and nonalarming.

        1. I am not sure about the 1930s, but here is an article from 1922 that indicates the Arctic ice was lower than it is now:

          The latitude cited (89 deg, 21 min) is still frozen as of now.

          I can’t vouch for the reliability of the source, but here are some images of what appear to be old newspaper articles about unusual warming:

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