Scientists have been trying to warn about the climate crisis for decades – but 2023 happened to be the year they perhaps didn’t need to. Science reporter Jamie Morton looks at four sobering statistics that tell the story.
Floodwaters gushing through Auckland Airport’s terminals; disaster-stricken Eskdale residents being plucked from their rooftops; cars sitting half-submerged on roads out of a cut-off Mangawhai.
The North Island’s extreme summer left us with more than enough dramatic images etched in our memory – and there’s also no shortage of new records to show just how off-the-charts it was.
The first six months of 2023 was New Zealand’s second warmest start to a year, but easily the wettest for a host of centres, with Kaikohe, Whangārei, Tauranga, Napier, Gisborne and multiple locations in Auckland all receiving a year’s worth of rainfall.
Even by the end of January, Auckland had already seen nearly half its average annual rainfall – and nearly nine times what it’d typically get in that month – with much of it coming in the disastrous Anniversary Weekend deluge.
On January 27, Auckland’s Albert Park was drenched with 280mm of rain in under 24 hours and 211mm in under six hours.
Just a fortnight later, ex-Tropical Cyclone Gabrielle brought the country’s costliest weather disaster in history, leaving swathes of Hawke’s Bay underwater, East Coast beaches covered in debris and 11 people dead.
Days from the end of summer, more record rainfall and plunging temperatures brought hailstones, slips and flooding to Mangawhai, stranding hundreds of people who had to camp at schools, in their cars, and strangers’ homes.
By the start of December, Auckland Airport’s rain gauge had collected nearly 1600mm, locking in yet another record for a year that had prompted MetService to issue five of its rare red warnings for extreme weather.
What caused the relentless wet?
We can blame La Niña’s subtropical influence on northern New Zealand, blocking highs near the South Island that caused rain-bearing systems to linger longer, and the energising effect of persistent, widespread marine heatwaves.
And, of course, there’s background climate change, which is packing more moisture into our atmosphere, while heating ocean waters in regions where many of our biggest rainmakers are sourced.
Gabrielle itself happened to form over waters that were running abnormally warm, even for the tropics.
While scientists haven’t yet teased out climate change’s precise hand in the monster storm’s effects, big deluges have become up to four times more common, and drop up to 30 per cent more rain, in the East Coast regions that it hit hardest.
As relentless rain saturated the north, seas at the other end of New Zealand warmed to reach some of the widest anomalies observed there.
It was yet another sign of marine heatwaves – prolonged spells of unusually high sea temperatures – that have been emerging around New Zealand over the past decade.
Above water, they have helped fuel our hottest-ever summer in 2017-18, while driving earlier grape harvests, milder winters and more energetic storms.
Below it, they’ve contributed to losses at salmon and mussel farms, sent tropical fish into normally colder climes and disrupted local feeding and breeding patterns of our own population of the planet’s largest animal: the blue whale.
In September, scientists warned warming waters were placing our kelp forests in peril thereby endangering the plethora of ocean species that rely on them.
At the peak of summer, meanwhile, seas around Fiordland warmed to a striking 5C above normal, heaping more pressure on sea sponges that had already just suffered a mass-bleaching event.
Data collected by MetService’s MetOcean Solutions showed multiple regions, including Bay of Plenty, Stewart Island, Chatham Island and Otago, recently experienced marine heatwave periods that stretched hundreds of days long.
“Event attribution studies show that it’s very-to-extremely likely that recent intense and perduring marine heat wave events in the Tasman Sea are due to human-induced climate change,” said the agency’s science lead, Dr João De Souza.
Again, natural drivers were also a big part of the picture; the windy arrival of El Niño helped churn up our seas and dissipate much of that stored-up heat.
In the long-term, however, scientists expect marine heatwaves to grow longer, stronger and more frequent under climate change.
On top of what we’ve already witnessed, scientists have warned that average sea temperatures could rise by 1.4C within four decades – and almost 3C by the century’s end.
That would mean that, by mid-century, we could be facing 260 days of marine heatwaves per year – and 350 days by 2100 – compared with the 40-odd days we see now.
Marine heatwaves and other drivers have also been taking bites out of our shrinking glaciers, which have lost about a third of their ice volume in just four decades.
When scientists took to the air in March for their annual health-check of the South Island’s snowlines, they found some low-elevation glaciers had largely disappeared.
Even much larger, iconic glaciers like the tourist-pulling Fox and Franz Josef had retreated markedly.
Whether the world can limit warming to 2C, or let it run to 4C, means the difference in whether half or more than 90 per cent of New Zealand’s icy wonders ultimately vanish.
On a far greater scale, scientists have grown increasingly worried about another striking absence of ice – that in the Southern Ocean.
On February 19, satellite data showed Antarctic sea ice at its lowest extent, at 1.77 million square kilometres, after net extent dropped below 2 million sq km for the first time over 2022-23.
Amid the winter season, the Southern Ocean was suddenly missing about 20 per cent of the sea ice that would normally be covering it – equivalent to an area roughly 10 times the size of New Zealand.
Some experts have suggested we’ve now crossed a tipping point, where this seasonally swelling and shrinking apron of ice around Antarctica won’t ever regrow to its former extent.
The potential implications of losing that ice long-term are profound, given its role in helping regulate our climate, driving ocean circulation, supporting a plethora of life and buffering Antarctica’s vast shelves and sheets.
The trend came as scientists this year catalogued a series of recent extreme events across Antarctica, including major iceberg calving events and the world’s largest recorded heatwave.
As July edged toward becoming the planet’s hottest single month in 120,000 years, with an average 16.95C, United Nations Secretary-General Antonio Guterres famously warned of a new era of “global boiling”.
Over that month, when global temperatures measured 1.5C warmer than pre-industrial times for a record 16 days, wildfires raged across Sicily and the Mediterranean Sea’s surface reached its hottest reading in four decades.
In North America, smoke from Canada’s wildfires left tens of millions of Americans under air quality advisories, while water temperatures off its West Coast peaked at nearly 5C above normal.
Elsewhere, China set its highest temperature record – a blistering 52.2C measured in Sanbao, Xinjiang, on July 16 – while record-breaking monsoon rains caused devastation in north India and Pakistan.
While climate attribution studies are ongoing, a Climate Central analysis found 80 per cent of the planet’s population experienced hotter temperatures than they would have in a world without climate change.
The year is now on track to be Earth’s hottest ever observed, and it’s possible 2023′s anomaly could be as high as 1.5C above the pre-industrial average.
Holding warming at that limit happened to be an aspiration of the UN Paris Agreement, which ultimately sought to rein in further temperature rises to 2C above pre-industrial times.
Yet, just before delegates from signatory countries, including New Zealand, began meeting for this year’s climate conference, scientists observed two November days that exceeded that 2C threshold for the first time, with weather variability accounting for about half the reading.
Niwa meteorologist Ben Noll considered what the warming Earth meant for extreme events like the North Island’s sodden summer.
“It was one of those cases where you think, what’s possible as the planet warms up? Well, we were shown that in 2023,” he said.
“It doesn’t mean that every summer, every year is going to have that type of weather – it’s not necessarily the new normal.
“But when you get compounding risk factors coming together with that long-term warming trend, and that moistening in the atmosphere, the potential for these extreme events is rising.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
Much of the South Island is set to plunge below 0C tonight and tomorrow.