What was New Zealand's costliest year for flood damage was also our warmest – sending a grim reminder, if we still needed one, that our planet is heating at an alarming rate.
Niwa today revealed that 2021 was the hottest year in more than a century of records, with a mean land surface temperature of 13.56C - or just shy of 1C above the 1981-2010 average.
That placed it above our previous warmest, 2016, as well as 2018, which began with a record-hot summer, and 1998, the year a severe El Nino fuelled a nightmare drought.
"Coming up to the end of last year, we knew it was going to be in the top three, but December was such a hot month that it wasn't even by a close margin that it beat 2016," Niwa climate scientist Nava Fedaeff said.
"It is alarming that we have had so much warmth, particularly in the last decade," she said, noting that seven of the past nine years have been among the hottest on the books.
"Hopefully it does open some people's eyes, if they're not already open – but this isn't anything particularly new. We've been seeing this for a while now."
For the year as a whole, it was the warmest year on record for 12 locations – including Auckland (at Whangaparāoa), Wellington (at the airport) Dunedin (Musselburgh), Kerikeri and Whitianga - and a further 50 spots saw annual average temperatures in the top four warmest on record.
Daily data based on Niwa's Virtual Climate Station Network revealed how just 26 per cent of days in 2021 featured below or well below average temperatures – compared with 19 per cent of days with near average temperatures, and 55 per cent with above average or well above average temperatures.
Victoria University climate scientist Dr Luke Harrington pointed out that, while 16 stations experienced some of their hottest ever days in 2021, only one experienced its coldest day on record.
"That about sums up climate change in New Zealand: in the future, every cold record broken will be accompanied by another five to 10 hot records, if not more."
It's now been nearly 60 months – or five years – since Niwa recorded a month of below-average temperatures relative to the 1981-2010 baseline.
The hottest spell of the year took hold over the country from January 25-28, a period when the mercury at Ashburton reached 2021's highest reading, 39.4C.
Fedaeff said the year was also characterised by a series of tropically-charged storms, which pushed weather-related insurance costs to an unprecedented $304.9m.
They included a disastrous May deluge that dumped 200mm of rain on the Canterbury foothills in just two days, and was later assessed to have been made 10 to 15 per cent more intense because of climate change.
Combined with 2020's $274m damage bill, and other under-insured and uninsured losses, it's estimated that severe weather in the past two years alone came with a billion dollar-plus toll.
Later in the year, Tower moved to raise some premiums based on flood risk, representing a symbolic "first step" in the industry directly and openly confronting climate change-driven hazards.
The Government has been developing its own national adaptation plan, along with a new act dedicated to tackling climate threats.
About 675,500 Kiwis live in areas already prone to flooding, with a further 72,065 living in the firing line of where some of the most dramatic effects of sea-level rise could hit.
Along with the background influence of global warming, Niwa scientists have attributed 2021's warmth to a mix of factors – including separate La Niña events and heated oceans.
Both of those elements were now helping drive unseasonably hot summer temperatures.
A separate climate indicator, called the tripolar index, had spent much of last year in a negative phase, which encouraged La Ninas and sea surface temperatures around New Zealand to be above average.
As well, an indicator called the Southern Annular Mode (SAM) – essentially a ring of climate variability that encircles the South Pole, but stretching far out to our own latitudes – was mostly positive, which tended to bring more sunnier, settled weather over the country.
Fedaeff said the SAM was positive 73 per cent of days last year – the fourth-highest value since 1979.
The year also delivered New Zealand's warmest winter – the previous record was set just the year before – along with its warmest June, its second warmest spring and its 10th warmest autumn.
In just 111 years, the average has risen by more than 1C. The starkest changes have come within the past three decades, when the pace of warming has tripled.
Globally, human activities are estimated to have caused approximately 1.09C of global warming above pre-industrial levels.
According to the record of global land and ocean temperatures spanning 1880 to 2020, the seven warmest years have all been since 2014, and the 10 warmest years have occurred since 2005.
"Every year we spin the roulette wheel of weather variability; however, like a casino, we have rigged the game, and the hothouse always wins in the end," Victoria University climate scientist Dr Nathanael Melia said.
"Aotearoa New Zealand sits in a privileged position globally to shelter from climate change.
"Deep in the South Pacific and surrounded by ocean, the effects of rising global temperatures due to climate change are moderated.
"However, our protective waters have been pulsing up to 3C recently, inexorably driving up our surface air temperatures."
The latest record results – picked early by veteran climatologist Dr Jim Salinger last week – come as Niwa scientists this month reported that extreme events like record-breaking heatwaves have been increasing at a faster rate expected even under climate change.
In the past decade, there were on average four to five times more extreme high temperatures than would be expected in a climate with no long-term warming.
Even with climate change considered, New Zealand still experienced two to three times more extreme high temperatures than expected.
Melia said higher background temperatures were only exacerbating extreme weather events around the country.
"Heat extremes are getting hotter, and extreme rain events are getting wetter," he said.
"Summer 2022 has continued at full throttle too, and with the weather variability wheel landing on La Niña, I wouldn't be surprised to see 2022 result in a back to back record."