Reanalysis reveals no significant global warming in New Zealand in the 20th century

New Zealand has one of the longest temperature-time series available.  In the past it has been reported that this data-set  confirms the view of global warming of just under 1ºC per century. But that is now highly suspect. A new paper reanalysing the data has been published and shows that the trend is less than one-third of what has been previously assumed.

de Freitas, C.R., Dedekind, M.O. and Brill, B.E. 2014. A reanalysis of long-term surface air temperature trends in New Zealand. Environmental Modeling and Assessment, do1 10.1007/s10666-014-9429-z.

AbstractDetecting trends in climate is important in assessments of global change based on regional long-term data. Equally important is the reliability of the results that are widely used as a major input for a large number of societal design and planning purposes. New Zealand provides a rare long temperature time series in the Southern Hemisphere, and it is one of the longest continuous climate series available in the Southern Hemisphere Pacific. It is therefore important that this temperature dataset meets the highest quality control standards. New Zealand’s national record for the period 1909 to 2009 is analysed and the data homogenized. Current New Zealand century-long climatology based on 1981 methods produces a trend of 0.91 °C per century. Our analysis, which uses updated measurement techniques and corrects for shelter-contaminated data, produces a trend of 0.28 °C per century.

Dr. Craig Idso writes:

De Freitas et al. report that, whereas the previous analysis yielded a trend of 0.91 ± 0.30°C per century, their analysis – which used updated measurement techniques and corrects for shelter-contaminated data – produces a trend of only 0.28 ± 0.29°C per century, which is a heck of a lot less than what had previously been believed to have been the case.

The significance of de Freitas et al.’s work is two-fold. First, the authors report that the old, contaminated data with the inflated warming trend has been “widely used as inputs for societal design and planning purposes” all across New Zealand. Second, de Freitas et al. note these data are “extensively used in hindcast verifications for regional and local models.” However, as the saying goes, “garbage in equals garbage out.” Therefore, at best, the corrected New Zealand temperature trend, which is three times smaller than the uncorrected version, calls into question all results, findings, conclusions, and policies built upon or derived from the old contaminated data record. And at worst, it invalidates them.

Given the great importance of starting with the proper baseline, one would hope that with so much at stake in terms of economics, personal freedoms, and governance, much greater care and scrutiny would be applied to ensuring the quality and reliability of near-surface air temperature records. But obviously, such has not been the case for New Zealand. And it begs the question as to where else temperature records might be less than par.

To obtain a “global temperature”, raw temperature data from available sites is massaged, applied to geographical grids, corrected, adjusted, “filled-in” and otherwise homogenised. But the algorithms used to make these adjustments inevitably carry the preconceptions and misconceptions of the adjusters. As raw data is reviewed it is becoming increasingly obvious (in the US, in Australia in Germany and now in New Zealand) that “adjustments” that have been made over the last 20 years have been plagued by “confirmation bias”. Rather than a clear-cut warming record what is apparent is that many data-sets have been adjusted to “cool the past”.


%d bloggers like this: