Source: Radio New Zealand
Two activists, sitting on the floor alongside the grave of Charles Darwin, after they sprayed “1.5 is dead” over it in protest against climate change in action, inside Westminster Abbey in central London. AFP / Just Stop Oil / Jamie Lowe
Climate activists sit by the grave of Charles Darwin inside Westminster Abbey, London after they sprayed “1.5 is dead” over it in protest.
Among the hoopla of the annual COP climate summit – this year being held in Belém in the Brazilian Amazon – there is one fact finally being spoken out loud.
Ten years ago, most of the world’s countries signed up to the central pledge of the Paris Agreement: to limit global warming to well below 2°C and pursue efforts to limit the increase to 1.5°C.
Until now, official discussions treated 1.5°C as though it was still live, despite projections showing it was increasingly tenuous. Even after the limit was breached for the first time across a whole year in 2024, scientists said keeping the long-term average to 1.5°C was still technically feasible.
But a new UN Environment Programme report, released just before COP30 started, declared that dream was over, and the best the world could now achieve was to spend as little time above 1.5°C as possible.
Speaking at the summit’s opening, UN secretary-general Antonio Guterres spoke plainly: “We have failed to ensure we remain below 1.5 degrees.”
The world needed to face that “moral failure” and do everything it could to limit further damage, he said.
So, what hope is left – and why does 1.5°C still matter?
Why was the limit set at 1.5°C?
The Paris Agreement target built on earlier, more vaguely-worded agreements to limit global warming to 2°C – identified by the scientific community as an absolute ceiling.
But many climate scientists agreed that even warming below that limit would have disastrous consequences, and they were joined by a large group of small island nations who, faced with oblivion, pushed over the years for the world to adopt a lower warming goal.
New Zealand climate scientist Dr Andy Reisinger, who is a climate change commissioner, but spoke to RNZ in his capacity as an independent consultant, said 1.5 is not a black and white dividing line, but there are important ‘tipping points’ – irreversible changes in Earth’s systems – that start kicking in at that level of warming.
“It’s very hard to pinpoint them exactly on a global temperature scale,” Reisinger said.
“Having said that, some tipping points, you know, we’re very confident that they do exist and that they’re not reversible.”
Among the first is the collapse of the world’s coral reefs. “That’s one tipping point where we know it’s at about 1.5 degrees,” he said.
The West Antarctic ice sheet is among major geophysical phenomena at threat of permanent loss if global temperatures keep rising. AFP PHOTO / NASA / HANDOUT
Other points on the scale are less clear, such as the slowing and potential shutdown of ocean circulation that keeps northern regions like Britain and Scandinavia warm enough to sustain their populations and grow crops.
“That shutdown… is something that we desperately want to avoid,” Reisinger said.
“The more we can limit warming to as close as possible to 1.5 degrees, the lower the chances are that such a tipping point actually occurs.”
The same goes for widespread drying in the Amazon.
“[That] would turn large parts of the Amazon rainforest into savannah-dominated ecosystems, which in itself is a massive loss of carbon to the atmosphere, but also huge destruction of livelihoods for indigenous people and of course ecosystems and animal species.”
When will we pass 1.5°C?
The short answer is: very soon.
“The data is showing that we’re getting very, very close to breaching global warming of 1.5 degrees,” Reisinger said.
2024 was the first year in which global average temperatures were more than 1.5°C above pre-industrial levels – but a single year does not define global warming.
“Global warming is normally understood as the long-term average across multiple years,” he said.
“The long-term warming trend is still below 1.5 degrees, but only just, and we expect that within the next five years or so, global warming, as a long-term average in global temperatures, will start to exceed 1.5 degrees.”
There are always scientific uncertainties present.
“If next year we discover that we got some measurements of global temperature in the late 19th century fundamentally wrong, we might find that we’re actually further away from 1.5 degrees than we think we are… but there’s an equal chance that it will be even more than it is.”
Is there any way to avoid breaching it?
Not really.
“Emissions would have had to fall rapidly from 2020 onwards, and they haven’t,” Reisinger said.
“And so we can’t turn the ship around anymore in the space of five years.”
Even in the late 2010s, it was still possible, but now the very best scenarios place peak global warming closer to 1.7°C – and that is increasing all the time.
“If we wait another five years, the very best scenarios will put us at 1.8 degrees. And so it goes. Time is not on our side in this.”
Why does it still matter?
If the world couldn’t limit warming to 1.5°C, it’s easy to question the point of persevering.
Reisinger said in fact, the world should be doubling down on its efforts, for two reasons.
The first is partly a legal and political one.
“The International Court of Justice has ruled that 1.5 is a central part of the ambition and the obligations that countries have towards maintaining a liveable climate.
“Once you pass 1.5 degrees, you can still get back to it, so it’s still a relevant target.”
The second is that 1.5°C “is not a binary black and white threshold”.
“It’s not like everything’s fine under 1.5 degrees and everything goes to hell in a handbasket above 1.5 degrees,” Reisinger said.
“Limiting warming to 1.6 degrees is better than limiting warming to 1.7 degrees. Limiting warming to 1.7 degrees is better than limiting warming to only 1.8 degrees… The lower we can keep that peak of warming, the better.”
Getting back to 1.5°C would still be better than giving up just because we’ve already breached it, he said.
“Of course, it would have been better if we had managed that, but we haven’t – so how are we going to deal with it?”
What is ‘overshoot’ – and can we get back to 1.5?
Earlier this year, Reisinger attended an event in Austria called the Overshoot Conference – the first global gathering of scientists to discuss the consequences of breaching 1.5°C of warming and the possible pathways to bend the curve back.
Dr Andy Reisinger was among scientists who met earlier in 2025 to discuss ‘overshoot’ scenarios. Supplied / Climate Change Commission
‘Overshoot’, in a climate science context, refers to exceeding the limit but then bringing it back to that level or below, he said.
“It’s not entirely infeasible… in the long run, even while accepting that we will be above 1.5 degrees for a period of time with attendant greater damages, greater harm from climate extremes, greater risk of tipping points.”
However, doing so will mean more ambitious action from governments, businesses and individuals.
“One thing that doesn’t change at all when we exceed 1.5 degrees is the imperative to reduce emissions in the near term as rapidly as possible, as much as possible, and towards at least net zero emissions of long-lived greenhouse gases,” Reisinger said.
That was the “absolute minimum” though.
“The inevitable consequence, once you actually accept it, would be to start talking about long-term net negative emissions – so, a scenario where countries take more CO2 out of the atmosphere than the totality of greenhouse gases they put into it, in order to enable the world as a whole to get back to lower temperatures.”
Would lowering temperatures again fix everything?
If we could achieve net-negative emissions, then the global temperature would come down again, Reisinger said.
“But the question is, would other parts of the climate system also reverse?”
There is much less certainty around that.
“Just because the temperature comes back down again, that wouldn’t turn on the ocean circulation that might have shut down… That would not magically regrow glaciers or the western Antarctic ice sheet.”
Tuvalu is among nations at risk of being irretrievably lost because of rising sea levels. AFP / Theo Rouby
Some geophysical systems, such as long-term sea-level rise, might experience a lag; others could be “irretrievably lost”.
Even so – going past 1.5°C is not the time to give up on mitigation, he said.
“You need to keep on going at the same pace, if not more so.”
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand