Garbage In, Garbage Out

(By Ken Stewart, assisted by Bill Johnston and Phill Goode; and cross-posted with Jo Nova)

Early ABC Radio news bulletins last Wednesday morning were led by this item, which you can read in full at ABC Online.

More climate scientists needed to avoid expensive mistakes, review urges

Apparently we urgently need 77 climate scientists to predict the future of areas like the Murray-Darling Basin with climate modelling.

Interestingly, Professor McDougall of the Australian Academy of Science points out that one of those “expensive mistakes” was the $2 billion desalination plant built in Queensland as a response to the millennium drought, “which really wasn’t an indication of climate change at all”.   Why didn’t the good professor raise his voice before the money was wasted?

But I digress.

Reliable modelling and projections for the future are surely desirable.

But such modelling must be based on reliable data, and the reliability of temperature data in Australia is demonstrably poor.

Example 1:  As has been widely reported in The Australian, and by Jennifer Marohasy and Jo Nova, cold temperatures at two separate sites (and possibly many others) were altered to appear warmer, then changed back, then deleted.  The BOM gave two conflicting explanations, both of which cast grave doubt on the reliability of “raw” temperature data from an unknown number of stations.

Example 2:  After enquiring why there are frequently two different temperature readings for exactly the same minute at various weather stations, a Bureau spokesperson told me that:

Firstly, we receive AWS data every minute. There are 3 temperature values:
1. Most recent one second measurement
2. Highest one second measurement (for the previous 60 secs)
3. Lowest one second measurement (for the previous 60 secs)

(See here and here.)

In other words, Australian maximum and minimum temperatures are taken from ONE SECOND readings from Automatic Weather Stations.  Spikes due to localised gusts of hot air, or instrument error, become the maximum for the day.  (This rarely has a large effect on minima, as night time temperatures are fairly smooth, whereas during the day temperature bounces rapidly up and down.  This is shown in this plot of temperatures at Thangool Airport in Queensland on Australia Day this year.)

Thangool 26 Jan 17 1 min

And this is for the same day between 3.00pm and 4.00pm.

Thangool 26 Jan 17 3 to 4pm

As you can see the temperature spikes up and down in the heat of the day by up to one degree between one minute and the next.  But these are the temperatures at the final second of each minute: during the intervening 59 seconds the temperature is spiking up and down as well, which we know because occasionally the highest or lowest temperature for the day occurs in the same minute as a final second recording on the BOM database (usually on the hour or half hour).  This can be up or down by two or three degrees in less than 60 seconds.

This is in contrast to the rest of the world.  The WMO recommends 1 minute (60 second) averages of temperature to be recorded to combat this very problem of noisy data, and this is followed in the UK.  In the USA 5 minute (300 second) averages are calculated.

From THE WEATHER OBSERVER’S HANDBOOK by Stephen Burt (Cambridge University Press, 2012):

Observers handbook

Even without software or human interference as in Example 1, this means Australian temperature data, in particular maxima, are not reliable.

Example 3:  Historically, temperatures were observed from Liquid In Glass (LIG) thermometers.  From the 1990s, Automatic Weather Stations (AWS) were installed using Platinum Resistance Thermometers (PRT) and are now the source for daily data.  AWS thermometers are very precise, but as I showed in Example 2, their data is used idiosyncratically to record 1 second spikes, frequently resulting in higher maxima and less often slightly lower minima than a 1 or 5 minute average.

One would think that with such a major change in technology there would be comparative studies reported in the BOM’s meteorological journal or other “peer reviewed” literature.  Apparently not.

Dr Bill Johnston has investigated this and says:

Parallel data were collected all over Australia for over a decade, some until last year when thermometers were removed, at manned sites, mainly major airports (Ceduna, Sydney, Hobart, Perth, Darwin, Alice Springs, Albany, Norfolk Island, Wagga to name a few) and also met-offices such as Cobar and Giles. However, comparisons between screens were done at one site only (Broadmeadows, Melbourne, which is not even an official weather station) using PRT only and reported as a “preliminary report”, which is available (https://www.wmo.int/pages/prog/www/IMOP/WebPortal-AWS/Tests/ITR649.pdf) however, after AWS became primary instruments, as I’ve reported before, the Bureau had an internal policy that parallel liquid-in-glass thermometer data were not databased. Furthermore, they had another policy that paper-data was destroyed after 2-years. So there is nothing that is easily available…. there is also no multi-site replicated study involving screen types and thermometers vs. PRT probes ….

Deliberate destruction of data is scandalous; the only way now to compare Automatic Weather Stations (AWS) and Liquid in Glass, is to hunt for sites where there is overlap between two stations; where the AWS is given a new number. This is possible BUT the problem is that the change-over is invariably confounded with either a site move or the change to a small screen.

Therefore we suspect that the introduction and reliance on AWS has led to artificially higher maxima (and thus record temperatures) than in the past, but we have no way of knowing for sure or how much.

So we now have (1) temperatures that are altered before they even become ‘raw’ data; (2) use of one second spikes for recording daily maximum and minimum temperatures, very probably resulting in artificially high maxima and slightly lower minima; and (3) no way of telling how the resulting data compare with those from historical liquid-in-glass thermometers.

How can the CSIRO hope to produce reliable climate modelling with any number of climate scientists when the BOM cannot produce reliable temperature data?  Garbage in, garbage out.

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One Response to “Garbage In, Garbage Out”

  1. Geoff Sherrington Says:

    Thank you Ken,
    This needed saying.

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