The world will likely exceed 1.5 degrees Celsius of warming within the next few years, according to a UN Environment Programme report. The report acknowledges this overshoot but argues the planet could theoretically cool back to 1.5°C by the end of the century through rapid emissions cuts and large-scale removal of carbon dioxide from the atmosphere.
The 1.5°C target, adopted under the Paris Agreement in 2015, has always faced steep obstacles to achievement. Inger Andersen, head of UNEP, said the goal remains important even after overshoot: "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."
The scenario described in the report would require limiting peak warming to no more than 1.8°C, according to Debra Roberts, a report author at the University of KwaZulu-Natal in South Africa. It would also demand a halving of global emissions by 2035, said Joeri Rogelj, another report author at Imperial College London. Emissions are currently rising worldwide.
The plan would require scaling up carbon removal to roughly 10 gigatonnes of CO2 annually, compared with current emissions of around 40 gigatonnes. Reto Knutti at ETH Zurich, who was not involved in the report, estimated this would require scaling carbon removal by a factor of around 100,000. While direct air capture technology could theoretically reach such volumes, Knutti said it is prohibitively expensive and the scenario is politically implausible.
Oliver Geden at the German Institute for International and Security Affairs said the overshoot concept, once a theoretical exercise, now risks becoming "official plan B" for the 1.5°C target. "The overshoot concept may turn out to be no more than a way to mask ongoing failure," he said. Among the latest climate scenarios used by modellers, only two imply a return to 1.5°C before 2150.