Aotearoa New Zealand has just experienced its warmest winter on record – well exceeding the previous record which was set just last year.
Official climate data from the National Institute of Water and Atmospheric Research (NIWA) shows winter 2021 (June to August) was 1.32°C degrees above average – last winter it was 1.14°C above average.
The figures, derived from the NIWA ‘seven-station’ temperature series which extends back to 1909, also show seven of the 10 warmest winters on record have occurred since 2000.
NIWA meteorologist Nava Fedaeff noted that there were 76 locations across the country that experienced a record or near-record warm winter.
Similar sequence of events 50 years ago
To put this winter’s record warmth in perspective, Fedaeff delved into historic weather records and found that the last time New Zealand experienced a similar sequence of events was 50 years ago.
The winter of 1970 was, at the time, New Zealand’s warmest winter on record – only to be beaten by the winter of 1971.
“What was considered to be unusually warm at the time is no longer considered unusual. The winter of 1971 now stands in 13th place [among] the temperature rankings, while the winter of 1970 is 18th,” she explained.
Fedaeff added what may have been considered record-breaking in 1970 is now considered near average. For instance, the once record-breaking winter of 1971 was actually 0.75ᵒC cooler than the winter New Zealanders have just experienced.
Carbon dioxide concentrations are higher
A key difference can be found in carbon dioxide concentrations measured by NIWA at Baring Head, near Wellington. In the early 1970s the concentrations were 320 parts per million; today they are 412 parts per million.
So, what did the two periods have in common? The years 1970 and 1971 were both La Niña years, featuring warmer than usual coastal sea temperatures and higher than normal pressure over and to the east of the country – which led to more northerly and north-easterly winds than normal.
The winters of 2020 and 2021 were also influenced by La Niña, warm coastal waters, frequent high pressure and more northerly and north-easterly winds than normal.
“These similar winters, decades apart, show us that there are key natural ingredients to getting a warm winter, but adding climate change to the mix is like taking the same recipe and swapping plain flour for self-raising,” Fedaeff said.