BoM copies me, inadequately

Yesterday’s post noted the appearance of station summaries at the BoM adjustment page attempting to defend their adjustments to the temperature record at several stations. Some I have also examined. Today’s post compares and contrasts their approach with mine.

Deniliquin

The figures below compare the minimum temperatures at Deniliquin with neighbouring stations. On the left, the BoM compares Deniliquin with minimum temperatures at Kerang (95 km west of Deniliquin) in the years around 1971. The figure on the right from my Deniliquin report shows the relative trend of daily temperature data from 26 neighbouring stations (ie ACORN-SAT – neighbour). The rising trends mean that the ACORN-SAT site is warming faster that the neighbour.

BoMdeniliquin Deniliquin

The BoMs caption:

Deniliquin is consistently warmer than Kerang prior to 1971, with similar or cooler temperatures after 1971. This, combined with similar results when Deniliquin’s data are compared with other sites in the region, provides a very clear demonstration of the need to adjust the temperature data.

Problems: Note the cherrypicking of a single site for comparison and the handwaving about “similar results” with other sites.

In my analysis, the ACORN-SAT version warms at 0.13C/decade faster than the neighbours. As the spread of temperature trends at weather stations in Australia is about 0.1C/decade at the 95% confidence level, this puts the ACORN-SAT version outside the limit. Therefore the adjustments have made the trend of the official long term series for Deniliquin significantly warmer than the regional neighbours. I find that the residual trend of the raw data (before adjustment) for Deniliquin is -0.02C/decade which is not significant and so consistent with its neighbours.

Rutherglen

Now look at the comparison of minimum temperatures for Rutherglen with neighbouring stations. On the left, the BoM compares Rutherglen with the adjusted data from three other ACORN-SAT stations in the region. The figure on the right from my Rutherglen report shows the relative trend of daily temperature in 24 neighbouring stations (ie ACORN-SAT – neighbour). As in Deniliquin, the rising trends mean that the ACORN-SAT site is warming faster that the neighbour.

BoMrutherglen Deniliquin

The BoMs caption is

While the situation is complicated by the large amount of
missing data at Rutherglen in the 1960s, it is clear that, relative to the other sites, Rutherglen’s raw minimum temperatures are very much cooler after 1974, whereas they were only slightly cooler before the 1960s.

Problems: Note the cherrypicking of only three sites, but more seriously, the versions chosen are from the adjusted ACORN-SAT. That is, the already adjusted data is used to justify an adjustment — a classic circularity! This is not stated in the other BoM reports, but probably applies to the other station comparisons. Loss of data due to aggregation to annual data is also clear.

In my analysis, the ACORN-SAT version warms at 0.14C/decade faster than the neighbours. As the spread of temperature trends at weather stations in Australia is about 0.1C/decade at the 95% confidence level, this puts the ACORN-SAT version outside the limit. Once again, the adjustments have made the trend of the official long term series for Deniliquin significantly warmer than the regional neighbours. As with Deniliquin, the residual trend of the raw data (before adjustment) is not significant and so consistent with its neighbours.

Amberley

The raw data is not always more consistent, as Amberley shows. On the left, the BoM compares Amberley with Gatton (38 km west of Amberley) in
the years around 1980. On the right from my Amberley report is the relative trend of daily temperature to 19 neighbouring stations (ie ACORN-SAT – neighbour). In contrast to Rutherglen and Deniliquin, the mostly flat trends mean that the ACORN-SAT site is not warming faster than the raw neighbours.

BoMamberley Amberley

The BoMs caption:

Amberley is consistently warmer than Gatton prior to 1980 and consistently cooler after 1980. This, combined with similar results when Amberley’s data are compared with other sites in the region, provides a very clear demonstration of the need to adjust the temperature data.

Problems: Note the cherrypicking and hand waving.

In my analysis, the ACORN-SAT version warms at 0.09C/decade faster than the neighbours. As the spread of temperature trends at weather stations in Australia is about 0.1C/decade at the 95% confidence level, I class the ACORN-SAT version as borderline. The residual trend of the raw data (before adjustment) is -0.32C/decade which is very significant and so there is clearly a problem with the raw station record.

Conclusions

More cherrypicking, circularity, and hand-waving from the BoM — excellent examples of the inadequacy of the adjusted ACORN-SAT reference network and justification for a full audit of the Bureau’s climate change division.

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