This summer has officially been the hottest on record, with temperatures 2.3degC hotter than average.
Until now, the hottest summer had been in 1934-35 where the temperature was 1.8degC above the 1981-2010 average.
Meteorologist Ben Noll from climate agency NIWA told RNZ said climate change and January's heatwave were the biggest factors in the high temperatures.
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"Our oceans around New Zealand have featured excessively warm conditions in the order of 2-4degC above average and in some pockets six or 7degC above average.
"If you had the same conditions, the same atmospheric set-up two or three decades ago, it's unlikely you would have experienced the anomalies or the difference from average being quite as extreme as it was in 2017/2018. That's indicative of the long-term trend of global climate change, global warning."
Mr Noll told RNZ the average might even increase thanks to the last four days of summer still to come.
One-hundred and eight places around the country recorded their hottest summer on record, 21 their second hottest and eight their third hottest.