FOR almost a year, climate scientists have sounded one clear message. The world’s totemic goal of holding average global temperature rises to 1.5°C is still technically within our grasp, but will slip without a dramatic course correction by humanity.

“Unless there are immediate, strong, rapid and large-scale reductions in greenhouse gas emissions, limiting global warming to 1.5°C will be beyond reach,” said climate scientist Valérie Masson-Delmotte last August, launching the first of three landmark reports by the Intergovernmental Panel on Climate Change (IPCC).

Yet, three months later at COP26 in Glasgow, UK, at the climax of a pivotal UN summit designed to alter the trajectory of our emissions, COP26 president Alok Sharma admitted that even with new commitments, 1.5°C was on “life support”.

Fast forward to this April and Jim Skea at Imperial College London, launching the third IPCC report, gave a deadline for when the pulse might flicker out. If countries fail to deliver more ambitious emissions reduction plans by the next UN summit, COP27 in Egypt this November, he said: “We may well have to conclude 1.5°C is gone.”

Even a paper published this week suggests that the window to 1.5°C is closing fast. Michelle Dvorak at the University of Washington in Seattle and her colleagues estimate there is already a 42 per cent chance that the world will exceed the milestone based on historical emissions alone. By 2032, across eight future emissions scenarios, there will be a 66 per cent chance we will be committed to exceeding 1.5°C (Nature Climate Change, doi.org/hxss).

Earth has already warmed by 1.1°C since pre-industrial times. The IPCC says we are headed for about a 3°C rise by 2100, although one recent study gives a best case of 1.9°C if Glasgow’s promises are fully delivered globally. Staying under 1.5°C means global greenhouse gas emissions must fall 43 per cent by 2030, compared with 2019 levels.

That is mind-bogglingly steep. History offers no precedent that comes close. The biggest annual emissions drop in modern history was 5.4 per cent in 2020, when large swathes of the world stopped working and travelling during the coronavirus pandemic. Emissions rose last year and may do so again in 2022. What’s more, no country has put forward bolder plans than it promised at or before COP26.

In the face of such inconvenient truths, has it become untenable to keep saying 1.5°C is possible? And if we do collectively accept that the prospects of meeting the goal are “dead”, would that paralyse or catalyse action on climate change?

To supply answers, it is worth recalling the goal’s origins. “The push behind 1.5°C did not really come from the science community,” says Robert Rohde at US non-profit organisation Berkeley Earth. Since 1996, the broadly accepted goal in political spheres was 2°C above pre-industrial levels. From around 2008, small island states argued that anything weaker than 1.5°C meant oblivion. A growing cast of allies agreed. Yet it still surprised many people when 195 countries signed off on aiming for 1.5°C for 2015’s historic Paris Agreement.

That political deal led to a seismic IPCC report in 2018, which starkly spelled out the difference in climate impacts between a 1.5°C fate and the more intense heatwaves, flooding and human suffering that would accompany a 2°C future. In turn, 1.5°C became the world’s rallying cry on climate change, from the lips of politicians to the placards carried by Extinction Rebellion and Fridays for Future campaigners on streets across the world.

Calculating the odds

Scientists have rushed to catch up with this new political aspiration. In 2018, there were 53 published scenarios that reached 1.5°C with little or no overshoot before returning to that target (see “Overshoot world”, page 10), says Skea. By this April, there were 97. But because global average emissions have kept growing instead of falling, the models underpinning those scenarios are creaking under the strain. The IPCC’s reports only include scenarios with a 50 per cent chance of staying under 1.5°C, compared with a 66 per cent chance of meeting 2°C.

Given how the odds are stacked, is it still helpful for scientists to maintain that 1.5°C is technically possible? “Well, here’s the thing: whether we meet 1.5°C or not, is not a scientific question. It is a political and a policy question,” says Katharine Hayhoe at Texas Tech University. “We [scientists] stay in our lane and say, ‘technically, looking at the amount of carbon in the atmosphere and the amount that we are producing every year, if we did X and Y, we would still have a Z per cent chance of staying below 1.5°C’.”

Alison Ming at the University of Cambridge says it is still helpful, because a 1.5°C world remains feasible. “I think it’s worth saying that this future is possible,” she says. However, she echoes Hayhoe, saying that scientists are just laying out scenarios rather than making predictions. Ming says the IPCC models everything up to the worst-case scenarios, which no longer look likely. “I don’t really see it as scientists pushing 1.5°C of warming,” she says.

Nonetheless, Rohde says some researchers are uncomfortable with the narrative around 1.5°C because they believe it is an unrealistic target. “It’s not the message I tend to emphasise, because 1.5°C is very hard,” he says. “Even if we have scenarios that get there, they involve very radical changes of the energy system happening very quickly. And even if that works on paper, it doesn’t seem like humanity is making the necessary changes.”

“Even if 1.5°C works on paper, it doesn’t seem like humanity is making the necessary changes”

For now, few public figures, scientists included, will concede that the temperature target is out of reach. But with Skea giving November as a deadline, and the IPCC saying in April that global emissions must have peaked before 2025 to keep the goal alive, at some point this decade, society may have to collectively admit we have missed the mark. What happens then?

“At some point, you’re going to have to rip the Band-Aid off, and it’s better sooner than later”

The fear is that such an admission would lead people to “give up” on taking action to curb emissions, says Hayhoe. There is already some evidence that younger people are more fatalistic about their ability to make a difference on climate change. Nick Pidgeon at Cardiff University, UK, says one risk, well understood in health psychology, is that scaring people too much about a problem without offering them solutions is usually unproductive. “There’s a danger that if people think it’s going be really, really bad, people may want to avoid the problem,” he says.

Still, failure to be frank about 1.5°C now could lead to issues later. “I don’t think the solution to that is pretending it’s not a problem for longer, because then you’re just building in more and more emphasis as if it’s some sort of magic number, and increasing the risk of fatalism when we pass it [1.5°C],” says Zeke Hausfather, a climate researcher at the Carbon Brief website. “At some point, you’re going to have to rip the Band-Aid off, and it’s better sooner than later,” he says. Despite the risks, Pidgeon thinks we need a public discourse about whether the target is slipping away. “That conversation has to be had,” he says.

Scientists are split on what humanity’s climate target should be if we acknowledge that 1.5°C is out of reach. Some would hold to it, others prefer an emissions goal, others think it is a question for politicians. However, all the researchers that New Scientist spoke to agreed that there needs to be some sort of target.

“As humans, you need a target,” says Hayhoe. “We understand instinctively there’s no magic number of cigarettes you can smoke before you experience lung damage. Yet somehow 1.5°C and 2°C have turned into these magic numbers, where if we hit 1.49995°C [it’s okay], if we hit 1.50001°C, it’s all over.”

Not a cliff edge

As scientists frequently point out, 1.5°C isn’t a cliff edge. It isn’t a precisely calculated moment at which we know we will hit tipping points that turn the Amazon into a savannah or commit Antarctica’s ice sheets to a rapid collapse.

Richard Millar of the Climate Change Committee, a body advising the UK government, says the number can still serve as a North Star, even if we cross it. The Paris Agreement commits countries to hold rises to “well below” 2°C and “pursue efforts” for 1.5°C. Both can still be our goal, says Millar. Moreover, he suggests that people coping with the impacts of a 1.5°C world may be more be inclined to support ways of bringing the temperature back down later this century.

Hausfather says the Paris deal’s language on 2°C is vague, but usefully so. Switching to avoiding 2°C as our main goal would mean aiming for as close to 1.5°C as possible, perhaps landing between 1.6°C and 1.8°C, he says. In parallel, he argues that we should start talking about these temperature goals in terms of when peak warming will occur, rather than warming by 2100, the basis that climate scenarios usually work on.

While most scientists maintain that 1.5°C is still technically possible, the majority of those New Scientist spoke to think the goal will be missed.

Hausfather points out that the rate the world is warming, at 0.2°C per decade, will continue as long as our emissions don’t decline. “It just seems like there’s not the type of political action needed to result in a rapid reduction of emissions,” he says.

The goal will be missed, says Rohde, because “nowhere have we been at the pace necessary”. And Hayhoe says: “I don’t see how we’re going to do it without overshoot.” She says there is simply no signal of a decline in the world’s annual emissions yet, despite progress in some individual countries. “Realistically, I don’t see how the policies can be implemented quick enough,” she says.

Andy Wiltshire at the UK Met Office says the emissions cuts needed are probably in excess of what is feasible for societies. However, he notes: “There’s always a chance we can still make it. There’s decent uncertainty.”

That uncertainty is important. The headline statements about how emissions will affect the planet’s thermostat – such as a 43 per cent cut charting a path to a 1.5°C world – “crush a huge amount of uncertainty in the Earth system under the proverbial table”, says Hausfather. Two obvious examples are carbon cycle feedbacks – such as a warmer world making soil release more carbon – and just how sensitive the climate is to rising CO₂ levels. That fuzziness means we may get the short straw: cutting emissions drastically and still ending with more than 1.5°C of warming. Or we may get lucky, and end up with less warming than expected.

Every degree matters

The idea of conceding that prospects for hitting 1.5°C are dead might seem irredeemably gloomy. But it is worth remembering the path we were on before the world adopted the goal in 2015. Five years earlier, climate pledges globally had us on track for up to 5°C of warming by 2100, an apocalyptic level that would be almost impossible to adapt to, given that we are already struggling to do so after heating Earth by just over a degree.

Humanity shifted the goalposts at Paris, prioritising 1.5°C over 2°C. We have made significant progress to even have a chance of landing somewhere between the two. History may yet judge failure on 1.5°C as a success, given how much the rallying cry has dragged societies in the right direction.

In the meantime, remember the mantra on the lips of scientists over the past year: that every fraction of a degree matters. “If we end up at 1.6°C, that’s better than 1.7°C; if we end up at 1.7°C, that’s a lot better than 2°C. If we ended up at 2°C, that’s a lot better at where we were heading 20 years ago, which was 5°C,” says Hayhoe. “Every bit of warming matters. Every year matters, every choice matters, every action matters.”

2100 warming projections

Expected warming given emissions changes based on pledges and current policies

The path to 1.5°C has become a cliff edge…

Each line shows the trajectory of annual emissions cuts required for a greater than 50 per cent chance of staying below 1.5°C, depending on the year that emissions peak

…but 2°C remains achievable

Each line shows the trajectory of annual emissions cuts required for a greater than 50 per cent chance of staying below 2°C, depending on the year that emissions peak