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In April 2026 the amount of carbon dioxide (CO2) in the atmosphere exceeded 430ppm. The last time Earth’s atmosphere contained more than 400ppm of CO2 was during the Mid-Pliocene ~3 million years ago. Sea levels were 10-25 metres higher, global average temperatures were up to 4°C warmer than they are today, and Antarctica was covered in forests. Unless we reverse course, we’re on a path for global temperatures towards the much hotter Early Eocene (Fig. 1).
This level or warming won’t happen overnight, for the same reason that it takes time for an oven to reach the temperature you set on the thermostat. Nevertheless, the planet hasn’t warmed this fast since the comet wiped out the dinosaurs at the end of the Cretaceous, 65 million years ago. The average global temperatures in 2026 and 2027 are on track to exceed 1.5°C (Fig. 2) While some of this can be attributed to an extreme El Niño, global temperatures are no longer returning to pre-El Niño conditions:
“Cool” years are now hotter than the “warm” years of the past: tracking global temperatures through El Niño and La Niña. – OurWorld in Data 2025
Instead of turning down thermostat, we’re cranking it higher by continuing to add more greenhouse gases into the atmosphere. The result? A staggering increase in the number, scale, and duration of ‘heat storms’ (Video 1 & Fig. 2):
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Click the screen grab to be taken to the online portal, which shows a rotating globe. The map tracks ‘heat storms’ similarly to other maps that track cyclones or extreme weather events across large regions. In this example, New Zealand was selected, then the preferred option:°C was selected (the default is °F). You can click on a location such as Methven or Auckland to see the details. Scrolling further down the online page reveals the number of people affected by different heat storms around the planet.
Extreme vs. average weather-related events
The chances of getting a warm year are increasing all the time. The chances of getting a cold year are decreasing all the time. When you look at shorter time frames, from day to months, it’s really about the chances of getting a very hot event, extreme high temperatures, or heavy rainfall, are what’s really impacting both ecosystems and human activities. It’s how extreme are changing that’s really important…As temperatures rise, the number of rain days decrease. So moderate rain decreases while extreme rain increases…more and more extreme rainfall events and floods, with concurrent impacts, including erosion and landslips. – Prof. James Renwick 2022
When Cyclone Gabrielle struck Hawkes Bay in January 2023 it provided some insight into the limitation of climate models. The 2020 NIWA report, Climate change projections and impacts for Tairāwhiti and Hawke’s Bay projected that under the RCP8.5 (worst-case) scenario the average maximum annual 5-day rainfall by the year 2081 would be 151.3 (+14.8)mm at Glengarry.
During the cyclone, the Glengarry site recorded 546mm of rainfall with almost 400mm falling in 12 hours at a maximum intensity of 56mm/hour.
Over New Zealand, an average two to three fold rise in frequencies of extremes occurs irrespective of seasons due to anthropogenic influence, with a mean temperature increase close to 1°C. – Thomas et al, October 2022
NIWA’s long-running ‘seven-station’ series shows NZ’s average annual temperature has increased by about 1°C over the past 100 years. – Annual Climate Summary 2025, Earth Sciences New Zealand
Extreme weather events are rising at a pace which exceeds expectations based on thermodynamic arguments only, changing the way we perceive our climate system and climate change issues…. The additional evaporation and rainfall tends to end up in heavy rain rather than alleviating drought: half of it comes down in the wettest 6 d(ays) each year. Even once global warming is stopped, we will see unprecedented extremes for a long time to come.
Just think of a former once-in-5000-year event which at 1.5°C warming may have become a once-in-50 year event. – Di Capua and Rahmstorf 2023
At many locations studied, the one-in-100-year extreme sea level event is now occurring at least once per decade. Sea levels are continuing to rise so coastal inundation events will be happening even more frequently over time from here… This week’s extreme wave event on the Wellington south coast reinforces the idea that we need to act now and develop response plans urgently. I trust our policymakers and politicians are listening. – Prof. James Renwick 2026
The takeaway message is clear. Existing climate models and weather forecasts are not always able to predict the magnitude of extreme (acute) events. This should be considered when looking at, for example, flood hazard mapping tools as the statistical probability of any AEP1% event may no longer be valid because they were calculated for a climate that no longer exists. In some locations, the probability of recurrence may increase to decadal (AEP10%) or even annual (AEP100%). That is, they may occur every year.
Impacts
Most plants and animals alive today—including modern humans, which have been around for only about 300,000 years—evolved to live in an atmosphere where the quantity of greenhouse gases kept in enough heat, but not too much. Adding so much more heat so quickly means that many plants and animals don’t have time to adapt. This is disrupting entire ecosystems, driving species to extinction and bringing pests and diseases into new areas.
Taken together, this is threatening multiple life-supporting ecosystem services without which we cannot live.
Heat thresholds for humans have been poorly defined in part because public-health bodies have over-relied on a theoretical study published in 2010… In that paper, researchers used mathematical models to define the ‘wet-bulb temperature’ (WBT) at which a young, healthy person would die after six hours. WBT is a measure that scientists use when studying heat stress because it accounts for the effects of heat and humidity. The models churned out a WBT of 35°C as the limit of human survival. At that threshold, the body’s core temperature would rise uncontrollably. But the model treated the human body as an unclothed object that doesn’t sweat or move, making the result less applicable to the real world… In a 2021 study, Kenney and his colleagues provided a better estimate: a WBT survival limit of around 31°C. They calculated it by tracking the core body temperature of young, healthy people under different combinations of temperature and humidity while they were cycling. – Nature News 2024
Ecosystems, species, wild populations, local varieties and breeds of domesticated plants and animals are shrinking, deteriorating or vanishing. The essential, interconnected web of life on Earth is getting smaller and increasingly frayed. This loss is a direct result of human activity and constitutes a direct threat to human well-being in all regions of the world. – Prof. Settele, Global Assessment Report on Biodiversity and Ecosystem Services
More frequent and intense extreme events, superimposed on long-term climate trends, have pushed sensitive species and ecosystems towards tipping points, beyond ecological and evolutionary capacity to adapt, causing abrupt and possibly irreversible changes. – IPCC; Climate Change 2022: Impacts, Adaptation and Vulnerability
Background image: @redcharlie Unsplash
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