A symbolic climate change threshold that's formed the focus of New Zealand's latest policy stocktake may be crossed within little over a decade, as scientists report the damaging consequences of global warming have arrived.
Arguably the most important climate change report to date – authored by 200 scientists and drawing on more than 14,000 studies – has been described by one top Niwa climate scientist as "nothing but bad news".
The sprawling Sixth Assessment Report, just released by the UN's Intergovernmental Panel on Climate Change (IPCC), found that human-induced climate change was now influencing weather and climate extremes across the globe.
And that warming was happening at frightening pace.
Even since the IPCC's last assessment report, in 2012, global surface temperature had risen by 0.19C.
With human activity already having pushed global temperatures to 1.1C above pre-industrial times, the planet is in a state perhaps not seen for more than 100,000 years.
A drought that used to occur once a decade now happened twice as often.
If nations couldn't keep warming within 1.5C above pre-industrial levels – something that New Zealand's Climate Change Commission just found our policies currently failed to reflect – the planet would see even more heatwaves, longer warm seasons, and shorter cold seasons.
And at 2C of global warming – the bottom line for commitments pledged by 200 nations under the landmark Paris Agreement - heat extremes would more often reach "critical" tolerance thresholds for agriculture and health, the report warned.
Either of those junctures could be reached sooner than we might realise.
The report confirmed that the chances of the world staying within the 1.5C level had now dropped to 67 per cent – and that nations could only pump another 400 gigatonnes of carbon dioxide (CO2) into the atmosphere before hitting that threshold.
At current global emission rates, this would happen within just 11 years – or within less than four of our election cycles.
The authors warned that, unless there were immediate, rapid and large-scale emissions reductions, limiting warming to close to 1.5C - or even 2C – would prove beyond reach.
Niwa principal climate scientist Dr Sam Dean said scientific advances in the attribution of extreme weather events have been recognised, allowing the IPCC to make stronger statements about recent extreme weather.
"Some hot events were found to be 'extremely unlikely' to occur without human influence and that climate change is 'likely' the main driver of increases in the frequency and intensity of heavy rainfall events observed since the 1950s."
Climate change was clearly intensifying the water cycle, the report found, bringing more intense rainfall and flooding, along with more intense drought in many regions.
As for the report's prognosis for the future, Dean said the outlook was "nothing but bad news".
In high latitudes of the globe, precipitation was likely to increase, but decrease over large parts of the subtropics.
Coastal areas would see continued sea level rise this century, bringing more frequent and severe coastal flooding in low-lying areas, and driving more erosion.
Extreme sea level events that previously occurred once every 100 years, for instance, could happen every year by the end of this century.
One "medium" emissions pathway – assuming CO2 levels peaked around 2040 and then began to fall to about half in the last decade of this century - could see temperatures reach around 2C between 2041 and 2060, and around 2.7C between 2081 and 2100.
A "high" emissions scenario, in which CO2 levels doubled by 2100, could result in an average temperature 3.6C higher than pre-industrial times before the next century began.
The worst-case "very high" pathway, when CO2 levels doubled even before 2050, could result in 4.4C of warming by century's end.
Each came with their own alarming implications for extreme weather.
With 2C of warming, for instance, the hottest day in a decade would be 2.6C warmer, relative to the climate as it was 150 years ago, while droughts would occur three times more than they once did each decade, and the proportion of intense tropical cyclones would grow by 13 per cent.
With 4C, a decade's hottest day could be 5.1C warmer than it was, droughts would grow more than five times more frequent, intense tropical cyclones would become 30 per cent more frequent, and the planet's snow cover extent would shrink by a quarter.
Climate change in NZ
"As a climate scientist, the updated knowledge presented here is as fascinating as it is impressive, and has enabled a doubling down on the IPCC's confidence in our now 'unequivocal' influence on the climate," said Dr Nathanael Melia, a senior research fellow at Victoria University's New Zealand Climate Change Research Institute.
"However, as a human, with a young family, combined with this understanding, the contents of this report are nothing short of terrifying.
"In the space of eight years since the last report, the language seems to have changed from a position of a 'warning, this could happen', to a position of 'brace for impact."
We could now expect, Melia pointed out, exponential increases to the frequency and intensity of extreme heat events with every incremental increase of global warming.
"For example, a once in 50-year heat event in an 1850-1900 climate is now about five times more likely, and nine to 14 times more likely at Paris climate agreement levels."
In line with the global average, New Zealand's land areas have warmed by around 1.1C since the start of the century.
Heat extremes had increased and the fire season had become longer since 1950 at many locations, while cold extremes and snow cover and depth, have decreased.
The report projected increased winter and spring rainfall in the west and south of New Zealand, but less in the east and north over those seasons.
In summer, we could likely expect more rain in the east of both islands, but less in the west and central North Island.
Victoria University climate scientist Professor James Renwick explained this shift could be partly explained by the fact the tracks of storms were moving toward the poles in many regions – notably across the Southern Hemisphere – while high-pressure regions in the subtropics were also expanding poleward.
"As is seen across the globe, New Zealand glaciers will keep retreating as the climate warms."
And although the temperature difference might seem small to most of us, the report found changes in several local impacts – from floods to drought and heatwaves – would become more widespread under a 2C scenario, compared with 1.5C.
Dr Nick Cradock-Henry, a senior scientist at Manaaki Whenua-Landcare Research, pointed out that drought was now our costliest hazard, and had already had a "marked impact" on a primary sector that depended on stable, long-term climate conditions.
"To ensure sustainable long-term futures for Aotearoa New Zealand, the report is a stark reminder of the need for adaptation."
Melting ice, rising seas
Victoria University glaciologist Professor Tim Naish said that, even if the world managed to stay within the Paris Agreement's 2C target, some "pretty serious impacts" remained unavoidable.
"This is certainly the case with rising seas, which will impact at least 800 million people by the end of the century."
Even as of 2018, the global average sea level was about 15cm to 25cm higher than in 1900, and 7cm to 15 cm higher than in 1971 – and this would keep rising to reach between 10cm and 25cm higher by mid-century.
While the projected "likely" range for global sea level rise by 2100 – between 44cm and 1.01m - hadn't shifted significantly since the last report – big unknowns about sea ice processes meant that dramatic rises by as much as 2m by 2100, and 5m by 2150, couldn't be ruled out.
"The elephant in the room continues to be our ongoing lack of understanding of how Antarctica's ice sheets will respond," Naish said.
As it stood, fellow Victoria glaciologist Professor Nick Golledge said we could have high confidence that the ice lost from West Antarctica in recent decades had exceeded any gain in mass from snowfall.
"And we have high confidence that this loss is largely due to increased melting of ice below sea level, driven by warming ocean water," Golledge said.
"On the other side of the world the Greenland Ice Sheet has also been losing mass over recent decades, but in Greenland this is principally due to warmer air, rather than ocean, temperatures.
"It is virtually certain that the melting of the two great ice sheets, as well as the many thousands of glaciers around the world, will lead to globally rising sea levels for the rest of the current century."
Golledge explained there were still processes at play that still couldn't be fully captured in computer models, largely because they took place over time periods longer than we had direct, satellite-based observations for.
"In Antarctica some of these uncertain processes could greatly accelerate the loss of ice, and potentially contribute an additional one metre to sea level by 2100."
Along with rising higher, the report found oceans had grown warmer and more acidic – with less oxygen and more potential for "marine heatwaves" that have engulfed New Zealand over recent years – as a direct result of human influence.
These shifts came with grave impacts on ocean ecosystems - and the people who relied on them – and would continue throughout at least the rest of this century.
In our region, the report found "enhanced warming" in the East Australian Current region of the Tasman Sea had been observed, and was projected to continue.
'A line in the sand'
Climate Change Minister James Shaw described the report as "sobering", and saw it as "a line in the sand" for setting hard mitigation policies.
"It underscores the severity of the climate crisis and the urgency with which we need to take action," he said.
"It also underscores the need for our Emissions Reduction Plan to be as strong as possible, and for it to be not just more strategies, but real actions that will make a difference sooner rather than later."
As they stood, New Zealand's climate commitments weren't ambitious enough to fit in with what was needed to limit warming to 1.5C.
This year, the Climate Change Commission found we were on track to undershoot our set 2050 target of net-zero long-lived gases by some 6.3 million tonnes of carbon dioxide equivalent – and that we couldn't keep planting our way out of tough action.
The commission recommended a wholesale transformation across virtually every corner of the economy – from the cars we drive and import, and the cows and sheep we farm, through to the energy we produce and consume, the forests we plant and the houses we build.
Moreover, it set out a radical transition that, while changing the face of our country forever, would largely all happen within the next 15 years.
Cabinet ministers were still assessing how those recommendations would fit into the Government's plan, which would lock in three five-year carbon budgets, and was due by the end of the year.
But Shaw said recently-announced measures – like a "feebate" targeting high-emitting vehicles – reflected how seriously the Government was taking the crisis.
For the rest of the world, University of Canterbury's Professor Bronwyn Hayward said it was time to set aside the "magical thinking" that technology would save us.
The IPCC itself noted that CO2-removal techniques still weren't yet ready to "achieve the scale of removal to compensate for current levels of emissions and most have undesirable side effects".
"Instead, we must take real actions to reduce emissions and protect people, biodiversity and businesses," Hayward said.
"It's critical that we stop hoping someone or something else will fix this if we hope to achieve the Paris Agreement of 'holding the increase in the global average temperature to well below 2C above preindustrial levels' - let alone 1.5C."
While the next IPCC reports discussed how emissions could be cut, Hayward said the hard work needed to begin now.
"Let's start the real changes in some of the most obvious areas so we can look our children in the eye and report on big actions, not just plans, in Glasgow in November," she said, referring to the next UN climate summit.
"Extreme weather events cannot be the future we leave for our children. it will never be easier to act on climate than it is now."