Analysis: Climate experts have said their piece: Will the world listen?

Extreme weather events like last month's Cyclone Gabrielle will become more frequent under a changing climate. Photo / Dean Purcell

The experts have officially said their piece, giving world leaders what they need to tackle our planet’s worsening climate crisis. Science reporter Jamie Morton explains.

Two years and three major reports, authored by hundreds of scientists and informed by tens of thousands of peer-reviewed studies.

For all of that, though, the United Nations Intergovernmental Panel on Climate Change (IPCC) might only have needed a single sentence to hammer home its big message to decision-makers: Acting now can secure a liveable, sustainable future for all.

That statement, from its chair Hoesung Lee, encapsulates a just-issued synthesis, that itself encapsulates a trio of scientific stocktakes comprising the sprawling, 7700-page Sixth Assessment Report (AR6).

Just like that comment, the latest report is chock-full of urgent warnings of fast-closing windows – a person born in 2020 may experience several degrees of warming in their lifetimes - but also hope for a healthier, more equitable planet.

By the numbers, some loom especially large: There’s the 1.1C by which we’ve already warmed the world, making once-a-decade droughts twice as frequent.

University of Otago senior lecturer Dr Daniel Kingston noted the IPCC’s “hugely meaningful” use of the term “unequivocally” in attributing that rise to human activities.

“Scientists are typically cautious and like to include many ‘ifs’ and ‘buts’ with their statements,” he said.

“To eliminate all doubt that humans are causing global warming highlights starkly just how overwhelming the evidence is in this case.”

Or, there’s 1.5C: The aspirational goal of the Paris Agreement and symbolic temperature threshold, beyond which lies even more heatwaves and disastrous floods.

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 last month's Gabrielle hit hardest. Photo / Mark Mitchell

At the current pace of climate change, the world could blow past that milestone within just five to 10 years – and then through the Paris pledge’s ultimate target of 2C within two decades.

The first chunk of the AR6, released in 2021, warned that, without rapid and large-scale emissions cuts, reining global warming within either of those points would prove out of reach.

Today’s report pointed out that, even under the lowest of emissions scenarios, that all-important 1.5C mark would be “more likely than not” met because of the increased, cumulative levels of CO2 we’ve pumped into the atmosphere.

What lay ahead?

According to a mid-range scenario – in which CO2 levels peak at around 2040, then hit the 2C point some time between 2041 and 2060 – this century might finish up being some 2.7C hotter than pre-industrial years.

Such pathways ranged from a highly-optimistic 1.4C of temperature rise by this century’s last two decades, to a very pessimistic 4.4C.

However, for the frequency of extreme weather events like those New Zealand’s seen this summer, every tiny fraction of warming mattered immensely.

“Every tenth of a degree warming from here will add to the impact of extremes, with more loss of life, infrastructure damage, reduced food security, and many other impacts,” said Victoria University of Wellington climate science professor James Renwick.

Victoria University of Wellington climate science professor James Renwick. Photo / Supplied

With just 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.

In New Zealand, particularly, we could expect major climate shifts such as wetter summers in the east of both islands, or rainier winters and springs in the west and south.

Baked-in impacts on our oceans and ice sheets also meant unavoidable sea-level rise over millennia – but deep and rapid emissions drops could change the long-term picture.

Under one low-confidence estimate, global mean sea level could rise by two to three metres over the next 2000 years if warming could be limited to 1.5C, or two to six metres in a 2C scenario.

In the nearer term, the world could expect up to 23cm of mean sea level rise by 2050 and up to 55cm by 2100 under lower-emissions scenarios – or up to a metre by 2100 in higher ones.

“1.5C-2C global warming is an irreversible tipping point for the Greenland and West Antarctic ice sheets, and intergenerational multi-metre sea-level rise will be unavoidable,” said Victoria University glaciology professor Tim Naish.

The AR6′s second volume, released last year, also found the world was moving far too slowly to adapt to climate change – especially in lower-income populations living in swelling cities.

It also projected that by 2100 the proportion of the world’s population exposed to deadly heat stress could climb from 30 per cent today to somewhere between 48 and 76 per cent.

As many as three billion people could experience chronic water scarcity from droughts if warming reached 2C – and up to four billion under 4C of global temperature rise – again with grim consequences for food production and ecosystems.

The final part in the AR6 trilogy, however, offered a hopeful, viable roadmap away from climate devastation.

By 2050, it was possible the right mix of policies, infrastructure and tech could pull emissions down by 40 to 70 per cent.

Again, the next few years would be crucial.

To eventually pull warming within 1.5C, for instance, global emissions would need to peak before 2025 at the latest and be nearly halved by the decade’s end.

Meeting the Paris Agreement’s ultimate target of 2C would also require a 2025 peak, but emissions falling by a quarter before 2030.

The global temperature would stabilise when carbon dioxide emissions were forced back to net zero: For a 1.5C world, that’d need to happen in the early 2050s; for 2C, the deadline would be around the early 2070s.

Elsewhere, today’s report pointed to a “rapidly narrowing window of opportunity” for climate-resilient development – and that going hard on mitigation efforts now could come with multiple health and economic benefits.

A New Zealand-based author, professor Bronwyn Hayward of the University of Canterbury, noted the need for those steps to be transparent and inclusive - particularly of local and indigenous knowledge.

Between 1990 and 2019, our gross emissions climbed by more than a quarter, while net emissions – which include carbon removals from land use and forestry – rose by around a third. Photo / Brett Phibbs

In the past few years, New Zealand has made unprecedented headway on climate policy, with its Zero Carbon Act, new five-year carbon budgets, agricultural emissions pricing arrangements and a forthcoming Climate Change Adaptation Act.

But critics have still accused the Government of moving too slowly – most recently after Cabinet dumped a batch of climate-focused policy – and Hayward herself said New Zealand’s rising domestic emissions made it an “outlier” compared with other countries.

Between 1990 and 2019, our gross emissions climbed by more than a quarter, while net emissions – which include carbon removals from land use and forestry – rose by around a third.

“We don’t realise that we are quite a significant outlier now, in the way in which our emissions are continuing to rise, when many other countries are really starting to make significant cuts,” Hayward said.

“And that includes the US and the UK.”

While New Zealand’s made up just about 0.17 per cent of the world’s gross emissions, on a per capita basis, the country ranked as the sixth-highest emitter among developed “Annex 1″ nations.

“Every country says ‘but we’re so small’ and it’s always the big countries ... but three-quarters of the world is small and they make up a significant [proportion] collectively.”

Renwick saw tackling the root causes of climate change as a huge opportunity for humanity, to bring about a more equitable and sustainable world.

“Failure to act will surely end in chaos,” he said.

“I really hope the governments of the world are listening – we have run out of time for thinking about the issue, now is the time for action.”