The greenhouse gas data, collected at Earth Sciences New Zealand’s monitoring station at Baring Head in Wellington, contributes to an international network of stations used to understand overall global warming.
Global concentrations of CO2 also hit a new record of 426ppm last year – a more-than 50% increase on pre-industrial levels (280ppm).
Carbon dioxide persists in the atmosphere for thousands of years, meaning concentrations of the gas – and therefore global temperatures – would continue to increase until the world stopped producing emissions.
New Zealand’s climate was changing at the same time, Stats NZ said.
Annual average temperatures had increased by 1.36C since 1908, when reliable records began, with winter averages rising particularly quickly.
Rainfall patterns painted a more complex picture.
Some places in the North Island now received more annual rainfall, while other locations – such as Tauranga and Whangārei – were significantly drier.
The South Island was generally getting wetter, Stats NZ said.
What was also clear was that more of the country’s rain was arriving all at once, during storms and other severe weather events.
At 11 of the 30 weather stations included in the analysis, the proportion of annual rain falling on “very wet days” had slowly increased between 1960 and 2025, at a rate of 0.6% to 1.8% a decade.
The vast majority of New Zealand’s extreme rainfall is driven by “atmospheric rivers” arriving from the tropics.
As the global atmosphere warms, it can hold more water vapour – meaning more rain when those atmospheric rivers do arrive.
Extreme rainfall can overwhelm stormwater and river management systems, causing flooding and destabilising land – leading to landslips.
Levels of methane also rise
Levels of methane in New Zealand’s atmosphere also slightly increased in 2025, from 1880ppm in December 2024 to 1890ppm in December 2025.
Overall, methane concentrations have increased 13.6% since December 1989, the first year the Baring Head station began monitoring the gas.
Methane is much shorter-lived in the atmosphere than carbon dioxide – which makes its inclusion in emissions targets controversial – but has a greater immediate warming effect.
New Zealand has pledged to reduce its emissions of both gases, although the Government weakened the methane target last year.
The 2016 Paris Agreement – to which New Zealand is a signatory, with almost every other country – pledges to keep global warming to well below 2C and pursue efforts to limit the increase to 1.5C.
In 2024, the annual global temperature increase surpassed 1.5C for the first time.
Researchers have said there is a strong likelihood that this year and next could break that record again, following northern hemisphere heatwaves and a burgeoning “super El Niño” that has caused ocean temperatures to spike dramatically.
This year a United Nations report found long-term warming beyond 1.5C was now inevitable, even if countries honoured their current emissions pledges.
Best-case scenarios now put the peak at 1.8C – beyond irreversible “tipping points” for some ecosystems, such as coral reefs.
The report said the world needed to do all it could to limit the “overshoot”, and then bend the temperature curve back down.
“This is by no means an acceptable or preferred pathway,” it concluded. “It is simply the best remaining option.”
Even so, the world now faced inevitable adaptation to the effects of climate change, it said.
New Zealand’s overall emissions are gradually decreasing, largely due to forestry offsets, rather than cutting emissions at their source.
The most recent Greenhouse Gas Inventory data, for 2024, showed total annual gross emissions (emissions at source) fell 0.1%, while net emissions (which include forestry offsets) fell 2%.