The official New Zealand Temperature Record is made up of historical temperature readings (raw data) and NIWA’s adjustments. Both of those components are unreliable.
The 169-page Report on the Review of NIWA’s “Seven-Station” Temperature Series, or the Review Report (RR), published by NIWA in December 2010 devotes very little space to that bane of climatologists — the urban heat island (UHI) effect. It has been long recognised that air temperature readings taken in towns and cities are affected by the heat absorption of concrete and tarseal surfaces; by exhausts of vehicles, aeroplanes and air-conditioners; and by structures which deflect wind and confine humidity.
Because a “heat island” is not representative of the wider region or country, most climatologists try to give them a wide berth. Wikipedia says that “the temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 10°F”.
A similar enemy of the climate archivist is “shelter” — trees or structures which interfere with the thermometer’s normal exposure to wind or sun, and thereby cause distortions.
The mean temperature impacts of both UHI and shelter are typically gradual, but non-linear. They are hard to detect and almost impossible to correct. Most climate archivists simply omit any sites suspected of being contaminated by UHI/shelter. Continue Reading →
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