Bureau of Meteorology Temperature Record Adjustments.

Temperature records for Sydney, Melbourne, Adelaide and more rural neighbours illustrated with versions by GISS / NASA  adjusted for urban warming compared to  the BoM versions by Torok and Nicholls , can be seen, click here.  Readers interested in the Torok & Nicholls adjustment methodology  which is a mix of  the empirical and comparative,  should read their paper.

The first example is from their adjusted Newcastle and is shown in Figure 1.   The first point to notice is in these recent years T & N have adjusted Newcastle to be much warmer over nearly  two decades from 1973 to ~1990, a feature that of course inserts a warming trend into Newcastle.    To the extent that for a few years Newcastle rockets up to be warmer than the Sydney heat island  by ~0.5 degrees.   Do T & N really think that this sudden onset of warmth not apparent in Newcastle's near neighbour Williamtown,  could possible be a real climatic feature ?

Looking at the heavy trace for Newcastle T&N notice that 1990 is warmer than 1991.   This is contrary to all other stations where 1990 is cooler than 1991.  So this point in the record gives the game away and is firm evidence  that a non climatic adjustment has been made.

Figure 1

Another example where there one of  the T & N adjustments generates a discodant signal is in Mount Gambier and as in the case of Newcastle above an icrease in warming  results.
Figure 2 shows the T & N version for Mount Gambier as the heavy trace and the rise in temperature from 1892  to 1893 has ended up being a much more significant event than in any neighbours.     The original Mount Gambier is well in step with the nearby Portland yet this negative adjustment is made in 1892.leaving this anomalously cool 1892 in Mount Gambier.
There is a good  case here for saying this adjustment is not justified.

Figure 2

Another point to come out of  Figure 2 is that after 1899 Cape Otway, Mount Gambier and Portland all fit fairly well as near neighbours should.    Then from 1884 to 1890 those three stations are in close agreement.   The period from 1891 to 1898 might be better homogenised by a lower key approach bringing Cape Otway into closer agreement to the two neighbours for those years.  This would not insert as much warming into the trends.

The Torok and Nicholls reaearch was partly funded by the Greenhouse Advisory Committee.

Posted 4, October, 2000

© 2000 Warwick Hughes,

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