2025 was second-warmest year on record for NZ's part of the world

An extensive marine heatwave and continued glacier loss are among the alarm bells ringing as New Zealand's part of the world recorded its second-warmest year on record.

The World Meteorological Society's (WMO) State of the Climate report found that the average air temperature for the region in 2025 was 0.37 °C above the 1991-2020 average.

It had already confirmed in March that 2025 was globally the second-hottest year on record.

Last year's marine heatwave, which affected waters around New Zealand, was the most extensive ever recorded in a year without an El Niño event, the organisation said.

"This is a worrisome sign for 2026, with a potentially strong El Niño event now developing."

Between 1999 and 2025, sea levels in the region rose at an average rate of 3.7 millimetres a year.

WMO Secretary-General Celeste Saulo said rising ocean temperatures and levels were already affecting people's lives.

"For many countries and territories in the South-West Pacific, the ocean is central to livelihoods, economies and resilience."

University of Waikato Professor Sandra Morrison said the report held "sobering messages of the impact of climate change and extreme weather disruption".

"We know that any increase in temperatures will have devastating impacts on the environment and people alike," she said.

The report singled out last year's devastating Tongariro National Park fire as among the events that were driven by or made worse by climate change, noting that the fire happened against a backdrop of record warm spring temperatures.

This year could also mark the complete loss of the last remaining tropical glacier in Papua, Indonesia, the report said.

Ice cover in Papua last year was estimated at just two percent of what had been observed in 1988.

In New Zealand - which is home to nearly all of the south-west Pacific's glaciers - glacier volume fell by 42 percent, or nearly half, between 2005 and 2023.

There was a 6.5 percent decrease between April 2022 and March 2023 alone, the report said.

University of Canterbury associate professor Heather Purdie had monitored glaciers in New Zealand's mountains for more than 20 years "watching and recording our ice volume shrinking away".

"We have already lost around 300 glaciers and more will follow," she said.

University of Otago associate professor Daniel Kingston said last year's near-record temperatures were notable for occurring during a La Niña event, which often reduced overall temperatures in the region.

"2025 was actually the warmest year that has occurred in this region without the presence of El Niño conditions - noteworthy in light of the El Niño event this is just beginning to unfold now," he said.

Climate forecasters have warned that this year's El Niño could be the strongest ever recorded - bringing heatwaves to parts of the Pacific, and likely dry and windy conditions to large parts of New Zealand.

University of Auckland Professor Karin Bryan said the report confirmed what local climate researchers were observing.

"I think the most concerning of all the indicators they review, is the steady creep upward of the ocean temperature," she said.

"Many species are already under threat due to direct anthropogenic effects such as run-off, fishing and habitat change, and do not have the resilience any more to deal with this additional threat."

As well as changing marine ecosystems, warmer oceans contributed to sea-level rise and changing ocean currents, and indirectly altered storm tracks, the report said.