WELLINGTON, June 28 (Xinhua) -- Global climate change is responsible for the warmest ever first half-year in New Zealand, the government's National Institute of Water and Atmospheric Research (NIWA) said Tuesday.
Numerous temperature records had been broken, or nearly broken, during 2016, according to NIWA, which has temperature records dating back to 1909.
Every month of the year to June had been at least 0.5 degrees centigrade warmer than the 1981 to 2010 climatological average, a record only achieved in two previous years: 1971 and 1998.
NIWA climate scientist Dr Brett Mullan said in a statement that February, at 2.2 degrees centigrade above average, was the second warmest February on record, beaten only by 1998.
March was the sixth warmest March; May was the warmest ever May; and March-April-May was the second warmest southern autumn after 1938.
For the six-month period, January to June, the current warmest years were 1938 and 1999, followed by 1998 and 1971.
New Zealand was experiencing June temperatures more than 1 degree above average, Mullan said.
If the mild conditions continued for the next couple of days, January-June 2016 would end up at 1.3 degrees above average, in clear first place as the warmest first six months of the year on record.
The exceptionally warm conditions were a consequence of two factors: the long-term regional warming trend owing to greenhouse-gas increase in the atmosphere, plus local "natural variability" adding extra warming this year.
"The natural variability acts like a 'tail wind,' pushing the local temperatures above the long-term trend," said Mullan.
"Two factors are important: sea surfaces temperatures in the Tasman Sea are exceptionally warm, persisting at more than 1 degree average since February 2016, and there has been more northerly flow than usual over New Zealand so far this year."
This year also had more northerly than normal, but nowhere near as extreme as 1938, indicating global warming had elevated temperatures regionally so that, even with less northerly airflow, 2016 temperatures surpassed those of 1938.
