The IPCC report incorporates recent research suggesting that the amount of carbon that humanity can emit while limiting warming to 1.5 °C might be larger than previously thought. The previous IPCC assessment, released in 2014, estimated that the world would breach 1.5 °C by the early 2020s at the current rate of emissions. The latest report extends that timeline to 2030 or 2040 on the basis of studies1 that revised the amount of warming that has already occurred.
“Every extra tonne of carbon that we dump into the atmosphere today is a tonne that will have to be scrubbed out at the end of the century,” says Myles Allen, a climate scientist at the University of Oxford, UK, and one of the lead authors of the report.
“I think we need to start a debate about who is going to pay for it, and whether it’s right for the fossil-fuel industry and its customers to be enjoying the benefits today and expecting the next generation to pay for cleaning it up,” Allen says.
But scientists have only “medium confidence” in the revised carbon budgets, says Thomas Stocker, a climate scientist at the University of Bern in Switzerland. He says that researchers will provide a more comprehensive look at the numbers in the next full climate assessment, which is scheduled to be released in 2021.
In the meantime, the newer and larger carbon budget could send the wrong message to policymakers, says Oliver Geden, a social scientist and visiting fellow at the Max Planck Institute for Meteorology in Hamburg, Germany. He fears that the IPCC report undersells the difficulty of achieving the 1.5 °C goal. “It’s always five minutes to midnight, and that is highly problematic,” he says. “Policymakers get used to it, and they think there’s always a way out.”