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The world is likely to overshoot 1.5°C of warming within the next few years, a report by the UN Environment Programme (UNEP) acknowledges. However, it says it is still possible to cool the planet back down to this level by the end of the century. Can it really be done? It isn’t impossible, but it certainly isn’t the most likely outcome.
The goal of limiting the increase in the average global surface temperature to 1.5°C above pre-industrial levels looked implausible even back in 2015, when it was adopted as part of the Paris Agreement. The UNEP report can be seen as an “official” acknowledgment of what many have been saying for years: that it is now certain that we are going to blast right past this limit.
But some aren’t giving up on the target. There are no good outcomes if we remain above 1.5°C, says Inger Andersen at UNEP. “Even if we exceed 1.5, let’s be very clear: that 1.5 target is still the goal. But now we need to approach it differently, from above.”
Much of the report looks at the consequences of overshooting 1.5°C and the need for adaptation to cope with the severe impacts this will bring. “We will see increased food insecurity, increased water insecurity, impacts on human health – physical and mental – danger to our homes and our infrastructure,” says Debra Roberts at the University of KwaZulu-Natal in South Africa, one of the authors of the report. “This will lead to the loss of livelihoods and certainly lives.”
The world isn’t prepared for overshooting 1.5°C, she says. “Therefore we have to advance our adaptation and development strategies to deal with those higher levels of warming, the greater range of risks and impacts… Adaptation needs to be transformational to allow us to plan for a changing world.”
There will be no going back to how things were, says Roberts. “Some losses will be irreversible, which means returning to 1.5 doesn’t mean we return back to the same world we left.”
But what exactly should we be preparing for? The report focuses on a scenario in which rapid emissions cuts and massive-scale removal of carbon dioxide from the atmosphere result in a return to 1.5°C of warming by the end of the century.
But achieving this would require limiting temperature rises to no more than 1.8°C, says Roberts. Beyond this, there will be cascading effects from all the irreversible changes that make it much harder.
However, restricting warming to this level requires a halving of global emissions by 2035, says report author Joeri Rogelj at Imperial College London. That seems highly unlikely given that emissions are still rising worldwide.
In addition to emissions cuts, the scenario envisaged in the report also requires carbon removal on a truly gigantic scale – enough not just to balance out hard-to-tackle emission sources, such as farming, and achieve net zero, but to go well beyond that to remove around 10 gigatonnes of CO2 each year. That compares with current emissions of around 40 gigatonnes.
This means scaling up carbon removal by a factor of around 100,000, says Reto Knutti at ETH Zurich in Switzerland, who wasn’t involved in the report. Cheap forms of carbon removal, such as planting forests, can’t be scaled up this much because there isn’t enough land. Direct air capture could be scaled up, but it is really expensive, he says.
Knutti thinks achieving this is technically and financially possible, but not politically plausible. “We should be honest when we talk to policy-makers and the public that this is not the thing to plan for,” he says. “I think the plan should be to adapt for at least 2 degrees, if not more.”
James Dyke at the University of Exeter in the UK is even less optimistic. “There are still no credible plans for large-scale carbon dioxide removal,” he says. “Human societies must adapt and prepare for a warmer and more dangerous world that will persist potentially for centuries.”
Konstantin Weber, also at ETH Zurich, points out that among the latest emissions scenarios that will be used by climate modellers, only two imply a return to 1.5°C before 2150. The scenario based on current policies suggests warming of around 3°C by 2100.
Until recently, overshooting and returning to 1.5°C was no more than a scientific thought experiment, says Oliver Geden at the German Institute for International and Security Affairs. Now it could become the “official” plan B for 1.5°C. “The overshoot concept may turn out to be no more than a way to mask ongoing failure,” he says.
But even if getting the temperature back down to 1.5°C isn’t likely, we have to try, says Weber. “We have to give it a shot. There’s no real alternative.”
“Now is the time to double down on climate action, not to give up on it,” says Andersen. “Every fraction of a degree avoided, every year by which overshoot is shortened, and every adaptation action taken will save lives, protect ecosystems and reduce economic losses.”
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