The New Zealand
Climate Science Coalition

5 August 2011 FOR IMMEDIATE RELEASE

NZ unaffected by human-caused global warming

No temperature increase in the last hundred years

The current emissions trading scheme (ETS) has no justification, because New Zealand has not been affected by global warming, whether of natural origin or human causes, in the last 100 years. When corrected with accepted scientific techniques, the official New Zealand Temperature Record (NZTR) shows that there has been no measurable change in mean temperatures during 1909-2009.

The historical data shows a warming rate of 0.29°C per century, while the corrected figure is 0.26°C per century. But both amounts are within the margins of error, and are effectively zero.

These figures were announced today by the New Zealand Climate Science Coalition, in releasing a new detailed study of the temperature records held in the ‘CliFlo’ climate database.

“This study generally follows in the footsteps of NIWA’s NZTR Review, released last December, except in one vital aspect” said Coalition chairman, Barry Brill, “The difference is that we have scrupulously followed the statistical techniques described in the scientific literature, while NIWA did not.”

“The seminal peer-reviewed paper is Rhoades & Salinger (1993) ‘Adjustment of Temperature and Rainfall Records for Site Changes’. This is the authority NIWA’s Minister (Hon Wayne Mapp) has cited repeatedly in Parliament. It is on the NIWA website and permeates their Review report.

“The Rhoades paper describes the series of statistical steps which are required for a valid data adjustment, including measurement of margins of error. NIWA adopted two of those steps but ignored four others. In consequence, their calculations were just plain wrong as the technical notes below demonstrate”, said Mr Brill

Mr Brill said there was a second peer-reviewed paper which had been ignored by NIWA and which dealt with urbanisation and shelter problems at New Zealand weather stations: JWD Hessell (1980) “Apparent trends of mean temperature in New Zealand since 1930”.

NIWA, the Crown Research Institute (CRI) which advises Governments on climate science, is also responsible for maintaining temperature archives. In constructing its “New Zealand Temperature Record” (NZTR), NIWA has made a series of random adjustments which produce a cumulative warming trend of 0.92°C over the last 100 years.

“The scientific literature is quite clear that such random adjustments should balance out over time” says Mr Brill. “Detailed work undertaken by the Coalition’s statisticians and scientists show that is exactly what happens to the NZTR when internationally accepted techniques are applied.

“The historical weather data shows a trend of 0.3° ± 0.3° per century – effectively zero” says Mr Brill. “And that’s the same overall outcome as the adjustments produce when they conform to international standards.

“It is widely accepted that New Zealand is partly insulated from any global warming by our surrounding oceans, but the extent and duration of that insulation is unknown. NIWA has stated that it expects New Zealand will experience a ‘discount’ of about 33% from any future worldwide warming trends.

“The NZCSC finding that New Zealand has suffered no material warming during the past century shows a 100% ‘discount’ from the 0.7°C trend experienced globally. In the absence of any evidence of change, the null hypothesis is that New Zealand’s established immunity will continue into the future.

“This is good news for all New Zealanders” said Mr Brill. “Our isolation may be a cost in economic terms, but it seems to be a clear benefit in environmental terms”.

Technical Notes

The Rhoades & Salinger (1993) technique involves the following steps:
1. Determine the timing of any site change shown in the metadata of a candidate station.
2. Confirm that the candidate station data was not contaminated by non-meteorogical effects, at the relevant time.
3. Identify neighbouring stations unaffected by any change points or known problems a year or two before and after the site change time. These are the reference stations. These reference stations should be as close as possible to the candidate station and share the same local weather conditions.
4. For all the stations, obtain the monthly temperature data. Then, starting at the site change point, calculate a temperature difference series by subtracting the previous year’s monthly value from each monthly value. This is the temperature difference series termed k=1 (12-month offset). Repeat using k=2 (i.e. subtract the value 24 months prior). This has the effect of removing seasonal variations, as well as determining differences year-on-year at each station.
5. Determine the correlations between the candidate station and each of the reference stations, using the k=1 series. Use a 4th power rule to calculate the weighting to be applied to each reference station from these correlations.
6. Find the difference between the weighted sum of all the reference series and the candidate series. This is the z-series. Do this using both k=1 and k=2 series.
7. Calculate the mean of the z-series, and determine the 95% confidence limits.
8. If the absolute mean of the z-series is less than the 95% confidence limits (i.e. the confidence interval contains zero) then do not make an adjustment. Otherwise subtract the mean of the z-series (from point 7) from all monthly values prior to the site change.

NIWA, in their method, have made the following omissions or changes:
1. Candidate station data are not checked for gradual contamination (except Auckland pre-1960);
2. Reference stations seldom share local weather conditions with the candidate station, and are usually in different climate zones.
3. NIWA uses annual mean temperatures, not monthly. They do not create the differenced series between monthly values at all.
4. Instead of taking a short symmetric period (i.e. 1-2 years) before and after the site change, they accept a different z-series of assymetric periods of approximately ten years before and after. Although similar in concept to the R & S z-series, it is prone to non-climatic influences - something the R&S method specifically sets out to address.
5. NIWA compounds this problem by not using weightings on their distant reference stations. The whole point of weighting each reference station is to exclude (or reduce the influence of) those stations showing some abnormal non-climatic behavior relative to the other stations.
6. NIWA does not calculate the 95% confidence limits of the monthly z-series in order to determine whether an adjustment is warranted. NIWA always applies their calculated shift. This means the NIWA method is 100% open to Type I errors (false positives).

Ends (1039 words)

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