RCP8.5, a high-emissions climate scenario deemed to be the “business-as-usual” model under which no efforts are made to curb climate change, has been removed by scientists. This model represented what was thought to be the worst climate change could get. But thanks to strides in renewable energy and emissions reductions, it is now largely considered improbable.
Lowering the ceiling
It is difficult to determine how climate change will affect the future “because how much the planet will warm depends in large part on what humans do,” said Vox. So scientists build scenarios or “structured guesses about how the next century might unfold under different assumptions about energy use, growth and climate policy.” These scenarios get updated approximately every seven years. In a new paper published by an international team of researchers, the worst-case scenario was scrapped.
Under RCP8.5, “nations would make no effort to cut emissions and expand fossil fuel use,” Andrew King, an associate professor of climate science at the University of Melbourne, said at The Conversation. By 2100, “carbon dioxide levels would almost triple, to 1,135 parts per million and the world would be around 4.5°C (8.1°F) hotter than the pre-industrial period.” Instead, the “new high-emissions scenario projects about 3.5°C (6.3°F) of warming by 2100,” said The Times.
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Scientists have been positing that the worst-case scenario for climate change was becoming less likely over time. Despite this, the “use of RCP8.5 in climate modeling has remained, in part, as a way to study what might happen under a ‘baseline’ scenario in which the world does nothing to tackle climate change,” said The Washington Post. Using this model, however, has also “provided fodder for attacks,” with skeptics arguing that “scientists, activists and the media have overstated the risks that actually exist and given outsized attention to the most extreme scenario.”
Raising the floor
President Donald Trump claims that climate activism has been used to “scare Americans, push horrible energy policies and fund billions into their bogus research programs,” he said in a Truth Social post. But these recently updated scenarios are a “sign the expansion of solar, wind, electric vehicles and batteries have slowed emissions growth,” King said. “Taking RCP8.5 off the table is a sign of progress.”
Making progress does not mean all is well. Along with RCP8.5, the updated scenarios “discarded some very low-emissions scenarios because nations are unlikely to slash their fossil-fuel use as deeply as many world leaders had urged,” said The New York Times. Essentially, the “scenarios are becoming less pessimistic but also less optimistic.” The new models show that it is no longer possible to limit global warming to the recommended 1.5°C (2.7°F) above pre-industrial levels.
The new worst scenario of a temperature increase of 3.5°C (6.3°F) “would still be a very much worst-case scenario with considerable climate impacts,” Detlef van Vuuren, a senior researcher at the Netherlands Environmental Assessment Agency and lead author of the updated climate scenarios, said to The Times. “The brutal math of climate change is this,” climate scientists Zeke Hausfather, Glen Peters and Piers Forster, said in a commentary about the updated scenarios: “As long as CO2 emissions remain above zero, the world will continue to warm.”
