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.
"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.