Climate outlook predicts 'rivers in the sky', heatwaves in the sea

Flooding in Henderson Valley, West Auckland in January. Photo: Supplied
Flooding in Henderson Valley, West Auckland in January. Photo: Supplied
Bigger, heavier 'rivers in the sky' - like the atmospheric river that brought record rainfall to Auckland in January - are on the cards as the planet heats, the latest report on New Zealand's climate says.Infectious diseases and pests will be more likely to spread, and it's "almost certain" (90 percent) new pests will become established here, especially as parts of the North Island became more suitable for sub-tropical species to thrive.

That is according to Statistics NZ and the Ministry for the Environment's Our Atmosphere and Climate 2023 report.

The actual impacts will depend on how much greenhouse gas countries produce, and various complex climate processes.

But, based the current trajectory, where countries are tackling emissions but not fast enough to meet the Paris Agreement target of keeping global heating inside 1.5C-2C, New Zealand can expect around another 1-1.3C of heating by 2050 on top of what it is already experiencing, it says.

Higher temperatures are already hitting New Zealand communities - but the most affected critters might be species such as kiwi, whio (blue duck) and North Island kōkako, which the report says are facing a "thermal squeeze".

It says although some species are moving to cooler areas as the climate warms, others (like kiwi) have limited ability to move - and endangered birds such as fairy terns could lose their coastal breeding sanctuaries to washouts as seas rise.

But Ministry for the Environment chief science adviser Alison Collins said there was plenty people could do to protect these species. Conservation efforts like those to save the whio could still rescue our native biodiversity, she said.

Changes so far

New Zealand's average air temperature has risen 1.26C since 1909, and that seemingly small change is already having huge impacts.

Extreme weather (causing floods, slips and droughts) is becoming worse, and happening more often, the report says.

In line with what climate scientists expected, the south of the South Island is getting wetter and the north of the North Island drier, with changing rain patterns set to get more noticeable.

Nelson flood damage in Atawhai in August last year. Photo: RNZ
Nelson flood damage in Atawhai in August last year. Photo: RNZ
Places that are seeing more rain also tend to be getting more of it in heavier dumps, over a short period, the report says.

On the other hand, there were more droughts bad enough to impact farming in half the places monitored (though a handful of places had fewer droughts), with Dannevirke coming out worst for drought time.

The frequency of extreme heat has doubled, and fire risk has risen in some places. An area larger than Hamilton burned in wildfires in the year to June 2021 alone.

Meanwhile, tropical cyclones happened slightly less often - but got more severe, it says.

One trend that is worrying environmental officials is the potential for more extreme events to happen back-to-back - like Cyclone Hale dumping record rainfall on Auckland in January, closely followed by Cyclone Gabrielle devastating the North Island in February. That leaves little time to recover.

Treasury has estimated the damage from cyclones Gabrielle and Hale together may total between $9 billion and $14.5b, and, the report says, costs from events like these are likely to increase.

Native species

As well as hurting people, the changes are causing problems for native birds and fish, the report concluded.

The ministries gathered evidence from published studies to produce the analysis.

New Zealand's native species have evolved to survive in the largely stable climate the country had for most of the past 10,000 years, it says.

The report cites a study saying populations of gulls and penguins, including little blue penguins, might be falling because hotter, more acidic oceans make it harder to find food. Carbon dioxide dissolving in the ocean raises its acidity. Further down the food chain, acidity makes it harder for crustaceans (like crabs, crayfish, shrimp) and molluscs to build their protective, calcium-based shells.

Photo: File
Droughts will likely get more intense in some areas, the report says. File photo
Native forests might be expected to change their mix of species in future, to favour more drought-tolerant trees, it says.

However, Collins said by fostering healthy forests and wetlands, New Zealanders could lessen the impacts of floods and storm surges.

Outlook for the future

Unlike the Our Atmosphere and Climate reports in 2017 and 2020, the latest update includes details on what to plan for in coming decades.

Collins said it was significant that the report concluded the globe was not currently on track to meet the Paris Agreement. Every country had a responsibility to act and cut emissions, she said, but New Zealand also needed to start adapting to the impacts of heating.

Hotter and more frequent marine heatwaves are on the cards, possibly becoming permanent by the end of the century, the report says.

The report also says heat will probably affect summers more strongly than springs and autumns, with the added effect of wetter summers for the east of both islands.

Droughts will likely get more intense, especially in the north and east of the North Island.

Dr Nick Cradock-Henry, of GNS Science, who helped review the report, said the message could not be clearer.

"Aotearoa is warming; it's us. We are sure. It's bad. But we can do something about it."

Vital statistics

 - Air temp: up 1.26C since 1909

 - Glaciers: 35 percent of ice volume lost

 - Emissions: 76.8 million tonnes (2021), up 19 percent since 1990

 - Biggest sources: Agriculture and road transport

 - Year-on-year change: 0.7 percent drop from 2020 to 2021, mainly because of a small drop in cattle and sheep numbers

 - Cars, buses and trucks: Emissions down 7 percent since 2018, influenced by Covid-19

 - EVs: Now 2 percent of the light vehicle fleet