The GHCN Temperature Adjustment Myth

Over the past few weeks, the internet has been lighting up with more absurd claims of scientific fraud. This time, the claim is that scientists have been deliberately falsifying the data in the publicly available GHCN (Global History Climatology Network) database in order to fake warming trends. As far as I can tell, the hype originated with the blog notalotofpeopleknowthat whose author, Paul Homewood, pointed out that the temperature measurements in this database had been adjusted, and some of the adjustments seemed erroneous. The notion of scientific corruption has since been popularized with eye catching titles such as, “The fiddling with temperature data is the biggest scientific scandal ever.” As usual, there is more hype than truth to these blog posts, and it is my intention to debunk the many false claims surrounding these adjustments.

Why are the data being adjusted?
I want to begin by acknowledging that Paul Homewood is correct that some of the temperature data in the GHCN database have been adjusted. The problem is that most people are misinterpreting the nature of those adjustments and the reasons for them. The GHCN is a massive database with temperature recordings from hundreds of stations all around the world. With that many stations, inevitably you will get occasional false readings either from a station malfunction or from a change in the area around the station. The GHCN Technical Report says the following:

In brief, adjustments are necessary because surface weather stations are frequently subject to minor relocations throughout their history of operation and may also undergo changes in instrumentation as measurement technology evolves. Furthermore, observing practices may vary through time, and the land use/land cover in the vicinity of an observing site can be altered by either natural or man-made causes. Any such modifications to the circumstances behind temperature measurements have the potential to alter a thermometer’s microclimate exposure characteristics or otherwise change the bias of measurements relative to those taken under previous circumstances.

So, the adjustments are being made with the intention of improving the accuracy of the data, not with the intention of falsifying it.

How are the data being adjusted?
If you read the anti-global warming blogs, you will no doubt get the impression that corrupt, money-loving scientists are sitting down and deliberately adjusting the data in a way that suits them, but this is hardly the case. The GHCN applies a Pairwise Homogenization Algorithm (PHA) to all of the data. In simplest terms, the algorithm compares proximate stations, looks for outliers, and corrects for them based on the data from other stations. So, for example, suppose that we had five stations relatively close together, and for a given year, 4 of them were consistently reading +/- 0.5 ºC of one another, but the fifth one consistently read 3 ºC below the others. This algorithm would then tag that fifth station as being inaccurate and compensate for it using data from the other stations.

There are two important things to note here. First, scientists are not picking and choosing which data points to modify. They are running the algorithm and it is selecting the data points. In other words, scientists can’t be doing anything dishonest, because they are letting a computer decide what points to modify.

Second, the algorithm is admittedly imperfect. This is inevitable in any sort of smoothing algorithm like this. Invariably, there will be some cases where the algorithm incorrectly identified an outlier and adjusted points that should have been left alone. This does not, however, mean that the algorithm is worthless, and it certainly doesn’t mean that scientists are being dishonest. In fact, scientists are well aware of the limitations of their computer programs and are constantly working to improve them.

Are the scientists doing anything dishonest?
The truly astounding thing about this is that people are touting these adjustments as evidence of scientific dishonesty. In reality, scientists have been extremely upfront and honest about these adjustments. It would be one thing if scientists had been making constant, deliberate adjustments for years without anyone knowing, then it was suddenly discovered that all the published records were adjusted and the true records were gone. Then, perhaps you could accuse scientists of being dishonest, but the reality is that every single iteration of the GHCN has clearly stated that the adjustments are being made and explained how and why they are being made. In what universe is that dishonest?

Further, the original, unadjusted data are still readily available. Nothing has been covered up or hidden. These adjustments are only being made to one of the many databases in which scientists store their records. To put this another way, scientists are well aware of the limitations of their algorithm, and they take that into account while running their models and making their calculations.

Do the changes matter?
Looking beyond the accusations of scientific fraud for a moment, we need to ask what impact these changes actually have. The answer is, not much. They make slight changes in the trends from certain stations, but when you look at the full data set, the overall trend is still that the planet is warming by an amount that cannot be attributed to natural causes. Adjusted or unadjusted, the data say the same thing: global warming is occurring, and it is out fault. So all of this hype is really pointless.

To summarize the key points:

  • The data are adjusted to improve accuracy, not to deceive.
  • A computer algorithm decides which stations to adjust, not greedy, dishonest scientists.
  • There are legitimate limitations to the algorithm, and scientists are aware of these.
  • From day 1, scientists have acknowledged that they are making adjustments, and they have made no attempts to hide what they are doing.
  • The original data are still readily available and are being used.
  • With or without the adjustments, the result is the same: we are causing the planet to warm.
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2 Responses to The GHCN Temperature Adjustment Myth

  1. luthermartin1517 says:

    LOL! Do you work for Biologos or what?


    • Fallacy Man says:

      Please do not troll or attack people. If you want to make a logical argument, that’s fine, but pointless things like this are unacceptable, and I reserve the right to block you if you continue to post them.

      Believe it or not, I had to look up “Biologos” because I wasn’t familiar with it. I get absolutely no money from this blog.


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