Summary

2024 was Aotearoa New Zealand’s 10th-warmest year on record. The nationwide average temperature …was 13.25˚C, being 0.51˚C above the 1991-2020 annual average. Of New Zealand’s 10 warmest years on record, eight have occurred since 2013 – NIWA

This century, climate change will alter New Zealand’s natural water cycle significantly. It will change how much rain and snow we receive, and at what time of year. It will change how much water is stored in the soil, snow, glaciers and aquifers. It will change how much water evaporates back to the atmosphere and how much flows through streams and rivers to the coast. And it will change the severity of droughts, floods and power shortages. – Deep South

Two-thirds of New Zealanders live in areas prone to flooding and rising sea levels – NZ Statistics, 2023

The number of people exposed to these hazards will increase as the climate changes. – p53 Draft Adaptation Plan for New Zealand, April 2022 (The final Plan was released August 2022)

• The oceans have absorbed ~93% of warming and are heating up 40% faster than the was estimated ten years ago.
• The Southern Ocean, which plays a major role in Aotearoa’s climate, is almost entirely responsible for ‘uptaking almost all the planet’s ocean warming‘.

This Southern Ocean warming and its associated impacts are effectively irreversible on human time scales, because it takes millennia for heat trapped deep in the ocean to be released back into the atmosphere. – Huguenin et al, 2022

In the Southern Hemisphere climate models consistently predict an almost year-round poleward shift in mid-latitude westerly winds as a consequence of global warming. This poleward shift is most notable in the cool season, April–September. – Speer et al 2022

• The atmosphere holds ~7% more water for every 1°C warming; resulting in more intense precipitation, and more heat = more energy, winds are getting stronger. But:

The condensation of water vapour to make rain droplets releases heat. This, in turn, can fuel stronger convection in thunderstorms, which can then dump substantially more rain. This means that the intensity of extreme rainfall could increase by much more than 7% per degree of warming. What we’re seeing is that thunderstorms can likely dump about double or triple that rate – around 14–21% more rain for each degree of warming. – Dowdy et al, May 2024

• We already are experiencing extreme weather and increased evapotranspiration (10% more since 2003), leading to plant stress.
• Any drop in emissions won’t reverse warming or return us to a ‘normal’ climate as there’s a long lag time between emitting greenhouse gases and their effect (see ‘the last time there was this much carbon dioxide in the atmosphere‘).
• This is increasingly costly for all of us in a multitude of ways, from marine heatwaves that supercharge NZ storms and affect fish and bird populations, to drought, floods (rain and/or rivers), rising sea levels, ocean acidification, and loss of critical ecosystem services we need to survive.