杏吧原创

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

鈥淯nless there are immediate, strong, rapid and large-scale reductions in greenhouse gas emissions, limiting global warming to 1.5掳C will be beyond reach,鈥� said climate scientist last August, launching the first of three聽landmark reports by the聽Intergovernmental Panel on聽Climate Change (IPCC).

Yet, three months later at COP26聽in Glasgow, UK, at the climax of a pivotal UN summit designed to alter the trajectory of聽our emissions, COP26 president Alok Sharma admitted that even with new commitments, 1.5掳C was聽on 鈥渓ife support鈥�.

Fast forward to this April and 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聽said: 鈥淲e may well have to conclude 1.5掳C is gone.鈥�

Even a paper published this week suggests that the window to聽1.5掳C is closing fast. 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掳C.

Earth has already warmed by 1.1掳C since pre-industrial times. , although . Staying under 1.5掳C means global greenhouse gas emissions , 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 . Emissions rose last year and may do so again in 2022. What鈥檚 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掳C is possible? And if we do collectively accept that the聽prospects of meeting the goal are聽鈥渄ead鈥�, would that paralyse or catalyse action on climate change?

To supply answers, it is worth recalling the goal鈥檚 origins. 鈥淭he聽push behind 1.5掳C did not really come from the science community,鈥� says at聽US non-profit organisation Berkeley Earth. Since 1996, the聽broadly accepted goal in political spheres was 2掳C above pre-industrial levels. From around 2008, small island states argued that anything weaker than 1.5掳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掳C for 2015鈥檚 historic Paris Agreement.

That political deal led to a聽, which starkly spelled out the difference in climate impacts between a 1.5掳C fate and the more intense heatwaves, flooding and human suffering that would accompany a 2掳C future. In turn, 1.5掳C became the world鈥檚 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

杏吧原创s have rushed to catch up with this new political aspiration. In 2018, there were 53 published scenarios that reached 1.5掳C with little or no overshoot before returning to that target (see 鈥淥vershoot world鈥�, below), 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鈥檚 reports only include scenarios with a 50 per cent chance of staying under 1.5掳C, compared with a 66 per cent chance of meeting 2掳C.

Given how the odds are stacked, is it still helpful for scientists to maintain that 1.5掳C is technically possible? 鈥淲ell, here鈥檚 the thing: whether we meet 1.5掳C or not, is not a scientific question. It is a political and a policy question,鈥� says at Texas Tech University. 鈥淲e [scientists] stay in our lane and say, 鈥榯echnically, 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掳C鈥�.鈥�

at the University of聽Cambridge says it is still helpful, because a 1.5掳C world remains feasible. 鈥淚 think it鈥檚 worth saying that this future is possible,鈥� she says. However, she echoes Hayhoe, saying that scientists are just laying out scenarios rather than making predictions. Ming says the聽IPCC models everything up to聽the worst-case scenarios, which no longer look likely. 鈥淚 don鈥檛 really聽see it as scientists pushing 1.5掳C of warming,鈥� she says.

Nonetheless, Rohde says some researchers are uncomfortable with the narrative around 1.5掳C because they believe it is an unrealistic target. 鈥淚t鈥檚 not the message I tend to emphasise, because 1.5掳C is very hard,鈥� he says. 鈥淓ven if we have scenarios that get聽there, they involve very radical changes of the energy system happening very quickly. And even聽if that works on paper, it doesn鈥檛 seem like humanity is making the necessary changes.鈥�

For now, few public figures, scientists included, will concede that the temperature target is out聽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,聽at some point this decade, society聽may have to collectively admit we have missed the mark. What happens then?

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

Still, failure to be frank about 1.5掳C now could lead to issues later. 鈥淚 don鈥檛 think the solution to that is pretending it鈥檚 not a problem for聽longer, because then you鈥檙e just building in more and more emphasis as if it鈥檚 some sort of magic number, and increasing the聽risk of fatalism when we pass聽it聽[1.5掳C],鈥� says , a聽climate researcher at聽the Carbon Brief website. 鈥淎t聽some point, you鈥檙e going to have to rip the聽Band-Aid off, and it鈥檚 better sooner than later,鈥� he says. Despite聽the risks, Pidgeon thinks聽we need a public discourse about whether the target is slipping away. 鈥淭hat conversation has to be had,鈥� he says.

杏吧原创s are split on what humanity鈥檚 climate target should be if we acknowledge that 1.5掳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 杏吧原创 spoke to agreed that there needs to be some sort of target.

鈥淎s humans, you need a target,鈥� says Hayhoe. 鈥淲e understand instinctively there鈥檚 no magic number of cigarettes you can smoke before you experience lung聽damage. Yet somehow 1.5掳C and 2掳C have turned into these magic numbers, where if we hit 1.49995掳C [it鈥檚 okay], if we hit聽1.50001掳C, it鈥檚 all over.鈥�

As scientists frequently point out,聽1.5掳C isn鈥檛 a cliff edge. It isn鈥檛 a聽precisely calculated moment at which we know we will hit tipping points that turn the Amazon into a聽savannah or commit Antarctica鈥檚 ice sheets to a rapid collapse.

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

Hausfather says the Paris deal鈥檚 language on 2掳C is vague, but usefully so. Switching to avoiding 2掳C as our main goal would mean aiming for as close to 1.5掳C as possible, perhaps landing between 1.6掳C and 1.8掳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掳C is still technically possible, the majority of those New 杏吧原创 spoke to think the聽goal will be missed.

Hausfather points out that the rate the world is warming, at 0.2掳C per decade, will continue as long as our emissions don鈥檛 decline. 鈥淚t聽just seems like there鈥檚 not the聽type of political action needed to result in a rapid reduction of聽emissions,鈥� he says.

The goal will be missed, says Rohde, because 鈥渘owhere have we聽been at the pace necessary鈥�. And Hayhoe says: 鈥淚 don鈥檛 see how聽we鈥檙e going to do it without overshoot.鈥� She says there is simply no signal of a decline in聽the聽world鈥檚 annual emissions yet,聽despite progress in some聽individual countries. 鈥淩ealistically,I聽don鈥檛 see how the聽policies can be implemented quick enough,鈥� she says.

at the UK Met Office says the emissions cuts needed are probably in excess of聽what is feasible for societies. However, he notes: 鈥淭here鈥檚 always聽a chance we can still make it. There鈥檚 decent uncertainty.鈥�

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

Every degree matters

The idea of conceding that prospects for hitting 1.5掳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, , an apocalyptic level that would be almost impossible to adapt to, given that聽we are already struggling to聽do so after heating Earth by聽just聽over a degree.

Humanity shifted the goalposts at Paris, prioritising 1.5掳C over 2掳C. We have made significant progress to even have a聽chance of landing somewhere between the two. History may yet聽judge failure on 1.5掳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. 鈥淚f we end up at 1.6掳C, that鈥檚 better than 1.7掳C; if we end up at 1.7掳C, that鈥檚 a lot better than 2掳C. If we ended up at 2掳C, that鈥檚 a lot better at where we were heading 20 years ago, which was 5掳C,鈥� says Hayhoe. 鈥淓very bit of warming matters. Every year matters, every choice matters, every action matters.鈥�

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