Frostgate 1 – Australian Bureau of Meteorology altering temperature data – rewriting Melbourne climate history by eliminating many frosts

Jointly with Ed Thurstan.
Since the mid 1990’s the BoM has produced several adjusted versions of Australian temperature history – these add more warming trend than the raw data show and many climate sceptics have been rightly critical of these BoM “high quality” (HQ) versions – what could be termed “stroked and tweaked” data.
In March the BoM released its latest version of adjusted temperature data termed ACORN SAT and time series of daily max and min ACORN data for 111 stations can be downloaded.
There has been criticism of the way BoM HQ or ACORN data reduces hot days from the past – particularly pre mid 20th Century – which increases the warming trend. But fancy arguments can be raised as to whether the temperature in the distant past was measured in an exactly equivalent manner to modern data. However frosts are a different matter – constituting a marker of air temperature independent of thermometers.
Examining both the ACORN daily minimum temperature data for Melbourne Regional Office (BoM Station 86071) and the raw BoM data we found many frost mornings in the raw data (minimums below 0 degrees C) that were altered to non-frost days in the ACORN version (minimums above 0 degrees C) – see this example from August 1944 where the BoM in their 2012 ACORN data wipe out 3 frost days.

However in this case it is bad luck for the BoM that the online newspaper archive of the National Library of Australia has the Argus newspaper for the 9th August 1944 reporting the “THIRD SUCCESSIVE FROST”.

These inconvenient facts expose the BoM as writers of climate fairy stories –
from what should be the best maintained set of weather instruments in the Nation – expertly observed.

6 thoughts on “Frostgate 1 – Australian Bureau of Meteorology altering temperature data – rewriting Melbourne climate history by eliminating many frosts”

  1. how scary is that! I think I asked you once Warwick if the BOM raw data is just that (raw with no homogenisation) and I think you answered ‘who knows’ but I may be mistaken

    what is your answer to that question?

  2. Gidday Val – The temperature data you can download here is raw and not homogenized. I would expect it is just tidied up by removing errors and typos.
    BoM data that is “homogenized” – what I term stroked and tweaked is –
    Torok & Nicholls data from 1996 –
    HQ data from the next decade –
    and now ACORN data released March 2012.
    The whole point of homogenizing is that they claim our raw data is not correctly recording the past.
    So the data is corrected for errors thus producing a more perfect record of the past.
    The problem for the BoM with frosts is that a frost is evidence of a certain marker temperature independent of thermometers. So if your homogenization is going to add or subtract frosts – then that is something that requires careful explanation. As you will see later – while the ACORN data for Melbourne eliminates some frosts – other ACORN station data create frosts where there were none in the raw data.

  3. thanks Warwick

    I’m off to Brisbane tomorrow for three days so I’ll check where you’re up to when I get back

  4. Here is a “Frost” story from Adelaide in 1933.
    It is an interesting read relevant to the frost and air temp difference.
    They seem to have a different readings from the air and ground.
    Note from Editor; On this site (unless otherwise stated) we are always talking air temperature in the standard BoM enclosures about 1.2m above the ground. Those are the readings most commonly reported by the BoM. Grass temperatures are another metric that can be looked up for some stations if people are interested.

  5. Curious that in 1944 they expected 20 frost days a year, whereas now they expect 1 a year. Global warming or UHI?

    Possibly confusion between the first being in suburbs (where they get more than the city still) and second average for the City.

    Where I live in the Adelaide Hills, we’ve just had our fifth frost. I noted that one occurred at -0.3 minimum on my thermometer, but the BOM minimum was 2 degrees. My thermometer must be inaccurate.
    Curiously, I’ve never noticed frost on the ground when the thermometer reads above 0, although some on metal post box.

    Warwick, if they keep “revising” recent temperatures, are they admitting that they can’t read a thermometer?

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