The Bizarre Case of Mackay 33119

What has the Bureau of Meteorology done to Mackay’s temperatures?

Mackay’s temperature records from the old Post Office, Te Kowai, and the Met. Office have been combined into one, and this has been “homogenised” by reference to Mackay’s neighbours.

But in attempting to justify their actions the Bureau has provided TWO lists of neighbour stations and TWO lists of adjustments at their website.

First, the list of “neighbour” stations used at Mackay (from the 28 page Adjustments document at http://www.bom.gov.au/climate/change/acorn-sat/documents/ACORN-SAT-Station-adjustment-summary.pdf ).

33119    Mackay Met. Office (Mt Bassett) 1960-2014 is the official Acorn site.

33046    Mackay Post Office  1910-1949  (4 km away)

33047    Te Kowai  1910-2011  (10 km)

33058    Pine Islet Lighthouse  (70 km)

39023    Cape Capricorn Lighthouse (335 km)

33013    Collinsville Post Office  (154 km)

39083    Rockhampton Aero  (283 km)

32005    Cape Cleveland Lighthouse (290 km)

33077    Pacific Heights (Yeppoon- 273 km)

32078    Ingham  (421 km)

39122    Heron Island  (380 km)

32037    South Johnstone Experiment Station (Tully- 517 km)

34002    Charters Towers PO  (329 km)

33001    Burdekin Shire Council (Ayr- 255 km)

33007    Bowen PO  (160 km)

39069    Walterhall (Mt Morgan- 300 km)

35019    Clermont PO  (246 km)

However, they provide a different list in the explanation for Mackay’s adjustments given at http://www.bom.gov.au/climate/change/acorn-sat/documents/station-adjustment-summary-Mackay.pdf at a link from the site above, and the two explanations are quite different.

Here is the second list, including four extras:

You can imagine the reaction of Mackay residents on finding that Mackay’s temperatures have been homogenised using Tully, Heron Island, Townsville, Mount Morgan, Charters Towers, Clermont, and their old rival, Rockhampton.  None of these places has a climate anything like Mackay’s.

Further, the Bureau claims that Townsville and Rockhampton are excluded from climate analyses because they are both affected by Urban Heat Island (UHI) warming, but here they have been included in the climate analysis of Mackay.

Now the lists of adjustments:

The matching adjustments are completely different, and there are three extra breakpoints detected by statistical means, with adjustments, including two extra for maxima.  So which set of adjustments was actually used?

Here is a chart of Mackay’s annual maximum temperature records. Suffice to say that the Mackay record is a mess, and good luck to anyone trying to homogenise it.

Fig. 1:

These are the results from applying the two lists of adjustments to the raw Mackay temperatures, to see which matches the Acorn records.

Fig.  2:   Calculated maximum temperatures (raw temperature with listed adjustments applied) minus Acorn temperatures.  Zero difference equals a perfect match.

Fig. 3:   Minima:

The original list given in the 28 page list of adjustments appears to be the one used for both maxima and minima.  Mackay Acorn maxima cannot be replicated with the Station temperature adjustment summary list, which has two adjustments clearly not used, and is moreover confusing and does not follow the protocol for 1939-1940.  Similarly, there is an additional adjustment for minima which does not match the Acorn record.

The summary list appears to have been put together in a hurry in an attempt to head off criticism about lack of transparency.  But why the different adjustments?

And were the actual adjustments justified?  A simple test is to find the differences between the station being homogenised and its neighbours.  If Mackay has been properly homogenised, the average difference after homogenisation should have a trend close to zero.  Here are the results:

Fig. 4:  Average differences in anomalies of the 10 listed neighbours for the period around the “statistical” breakpoint at 01/01/1971.

The adjustment of about -0.3C for all years up to 1970 makes the differences worse.  Interestingly, when the two most distant sites to the north and south are excluded (South Johnstone and Heron Island), the trend in raw difference is almost zero.  The raw Mackay MO record is similar to the neighbours, without any adjustment.

Fig. 5: As for Fig. 4, but excluding 2 distant sites:

The adjustments to the Post Office for 01/01/1941 and 01/01/1948 cause the following differences:

Fig. 6:

Once again, there is a major difference between the Acorn record and the average of the neighbours, as shown by the steep trend- not much better than the raw difference.

To conclude,

1. the Bureau has made an embarrassing mistake in publishing two different lists of adjustments and neighbours for Mackay
2. the adjustments listed in the Mackay station adjustment summary are not those actually made
3. adjustments are based on “neighbours” up to 500 km away, including two with UHI effect
4. very few of these neighbours have climates similar to Mackay’s
5. differencing shows that homogenising makes Mackay Met Office maxima LESS like the neighbours, and Post Office maxima not much closer.

If the adjustments at Mackay are, as the Bureau claims, “indicative of the sorts of adjustments made across the 112 ACORN-SAT sites”, then we can look forward to finding many more problems.

Tags: Acorn, adjustments, Bureau of Meteorology, Mackay, temperature