Nothing random about NIWAGuest author | January 26, 2011
Loaded dice for temperature record?
In producing a new temperature record for New Zealand (NZT7), NIWA has again adjusted the raw measurements. Whilst no systemic error was found, one-off issues were raised by random site changes, especially during the early decades of the 20th century.
Curiously, NIWA’s adjustments are not random. Instead, their changes display a near-perfect symmetry, where amplitude is directly proportionate to age. Small adjustments apply to the 1950s, grow larger back in the 1940s, and larger still in the 1930s – before reaching their apogee in 1910-20.
Could this have happened by chance?
The NIWA NZT7 was ‘reviewed’ by the Australian Bureau of Meteorology (BoM). On an earlier occasion Dr David Jones, Head of Climate Monitoring and Prediction at the BoM, said:
“On the issue of adjustments you find that these have a near-zero impact on the all-Australian temperature because these tend to be equally positive and negative across the network (as would be expected given they are adjustments for random station changes).”
The NZT7 is represented by a graph covering the 100-year period 1910-2010, and aims to measure the temperature trend (in °C/century) during that period. Such a trend will be more pronounced as a result of either downward adjustments in the first part of the period (2010-75) or upward adjustments towards the end. The impact of an adjustment is determined by its size and the number of years it is applied.
The NZ Climate Science Coalition has listed the NIWA changes in a ‘NZT7 Schedule of Adjustments’ available from this site. (You can download the raw data in a spreadsheet (27 KB) or a pdf (13 KB).) The Coalition has quantified each adjustment and identified whether it has a favourable or unfavourable effect on the NIWA hypothesis that temperatures warmed throughout the last 100 years.
NIWA made 29 adjustments
- In all seven stations, the adjustments created or added to a warming trend.
- Twenty-one adjustments were trend-favourable while eight were unfavourable. So, by number, 73% of the ‘corrections’ favour an upwards trend.
- The trend-favourable moves (time-weighted) sum to 120.3°C whilst 16.2°C go the other way. So, by impact, 88% of the ‘corrections’ favour an upwards trend.
The ratio of almost 9 out of 10 adjustments being ‘helpful to the hypothesis’ is remarkable. But the symmetry of the NIWA adjustments, shown in Figure 1, adds further interest:
The graph shows the adjustments prior to 1974 are not only uniformly negative but also virtually linear with time, becoming greater the older the data.
What could be less random?
NIWA say the results are “unbiased”, and we must accept that there was no deliberate intent to mislead. But the problem of unconscious confirmation bias is well known to science, and it is particularly pervasive when the analysis is almost wholly subjective – as in the NZT7 case. It can be detected only by examining the outcomes and posing the question: “Would a reasonable bystander accept that these results occurred by chance, rather than by subconscious preference?”
Let’s all ask ourselves that question.