Climate analysis: 2020 was also a hot year for wider NZ region

A fisherman tries his luck at Pilot Bay, Mt Maunganui, on a sunny day last November. The year finished up one of the warmest NZ has seen on and off the water. Photo / George Novak

Last year wasn't just the one of the 10 warmest for New Zealand, but for our wider ocean territory too, new figures show.

Climate scientist Professor Jim Salinger says his calculations - putting 2020 as the ninth hottest year on record for New Zealand's combined land and ocean region - underscores the need for urgent action to slow the pace of warming.

According to the country's official, Niwa-run "seven stations" temperature series, which Salinger pioneered, 2020 was New Zealand's seventh warmest in 110 years.

The nationwide average of 13.24C followed a climate change trend that's put six of our past eight years among the hottest ever recorded, and driven a run of 47 straight months without overall below-average temperatures.

New Zealand's official average temperature for 2020 - calculated using the seven-station series - proved the seventh warmest on record. Image / Supplied

Salinger said a wider picture could be seen when more climate stations and ocean temperatures were added.

Nonetheless, it was one also consistent with a changing planet.

Sea surface temperatures across some four million square kilometres of New Zealand's exclusive economic zone averaged 14.16C last year, which was 0.38C above normal and the 11th warmest recorded.

And an extended dataset for land temperatures, covering 22 stations, recorded a 2020 average of 13.75C - 0.58C above normal and the eighth warmest year in that series.

When those ocean and extra land temperatures were put together, the result was 13.93C - or 0.39 above average and the ninth hottest year in a combined record stretching back 150 years.

Salinger said it was critical to consider how New Zealand's sprawling marine estate was also warming, given its economic and environmental importance to our country.

Some 20 times larger than our land mass, New Zealand's ocean territory supported a marine economy estimated to be worth $4 billion a year.

The resources it depended on were being increasingly threatened by rising ocean temperatures.

The Tasman Sea, particularly, was warming at one of the fastest rates on Earth - up to three times the global average.

Some 20 times larger than our land mass, New Zealand's ocean territory supports a marine economy estimated to be worth $4 billion a year. Image / Ministry for the Environment

"If we're in a situation where we effectively have a warming bath, that's going to affect us dramatically," he said.

"These figures really show that warming is leaping ahead, and we need to get on to it now, both in terms of mitigation and adaptation."

The stocktake comes after Salinger, with fellow scientists Professor James Renwick and Dr Howard Diamond, published findings showing the New Zealand region had warmed by 0.66C since 1871.

All of the hottest years had been logged since 1998, in step with global warming.
Salinger noted that a La Nina system had an influence on 2020's ocean temperatures.

The naturally-occurring climate driver's formation later in the year co-incided with coastal waters around some parts of New Zealand approaching marine heatwave conditions.

The Southern Annular Mode, or SAM - a key climate indicator - was also in a positive phase for periods of 2020, bringing westerly winds farther south over the southern oceans but lighter winds and sunnier skies over New Zealand.

As at this week, our coastal waters were running warmer than normal - ranging from 0.5C to 0.9 above average - but sea temperatures were expected to drop with a coming southerly change.