Over the last few weeks, the United States right loudly claimed victory in a battle that few people on earth knew was happening. The National Review’s Editorial Board gloated, “Science Has Spoken Against Climate Alarmism.” Several papers owned by Rupert Murdoch ran similarly hyperventilating headlines that scientists had reversed “doomsday predictions” and “quietly scrapped the apocalyptic forecasts that have terrified policymakers and the public.” Donald Trump wrote on social media that the United Nations’ “TOP Climate change committee,” the Intergovernmental Panel on Climate Change, or IPCC, “admitted that its own projections (RCP8.5) were WRONG WRONG WRONG!”That isn’t what happened. And it’s hard to overstate the gulf between the scale of the right’s triumphalism and the size of the thing they are ostensibly talking about. The alleged victory in question is in reality an academic paper published last month by a team of Earth system modeling experts convened by the Coupled Model Intercomparison Project, or CMIP, an initiative of the UN’s World Climate Research Program. The paper describes several new forward-looking climate scenarios created to help researchers understand how and why the earth warms, and what might happen as it does. Such scenarios have been a mainstay of climate science since the 1980s, and are updated frequently to account for new research and observations. “These scenarios are not prediction machines,” said Detlef van Vuuren of the University of Utrecht, a veteran of emissions scenario development and the lead author on the CMIP paper. “They are simply ways to explore possible futures.” As the present changes, so too do researchers’ models of possible futures.So what exactly was Trump celebrating? The CMIP paper—which was published in April—notes that its researchers now consider one older scenario “implausible.” First created in the early 2010s, RCP8.5 outlines a world that is between 4.2 and 5.4 degrees Celsius warmer by 2100, thanks to extremely high levels of coal burning. Somewhat confusingly, the “8.5” in RCP8.5 doesn’t refer to temperature degrees but to specific levels of radiative forcing—a measure of change in the earth’s energy balance caused by human-caused greenhouse gas emissions. It was also developed at a time of rapidly rising fossil fuel use and relatively expensive renewables. “RCP” itself stands for “representative concentration pathway,” meaning that it was chosen to represent a range of similarly dire preexisting scenarios. Importantly, RCP8.5 was always intended as a “low-probability, high-risk” scenario among several others that show much lower radiative forcing, emissions, and warming. RCPs 2.6, 4.5, and 6.0 appeared prominently alongside RCP8.5 in the fifth assessment report of the UN Intergovernmental Panel on Climate Change, released in 2013. In 2017, modelers replaced RCPs with something called “shared socioeconomic pathways,” and used RCP8.5 to inform the high-end SSP that appeared in the IPCC’s sixth assessment report in 2023. (The IPCC does not create its own scenarios or conduct original research, but relies on largely volunteer experts to synthesize the latest-available climate science across a range of topics every few years.)Some 15 additional years of observable data about climate change, real-world climate policy, and the relatively recent, rapid proliferation of cheap renewables have now made the coal-heavy world of RCP8.5 look much less likely than it did in 2013. “We’re now in a very different position than RCP8.5 would have taken us, which is good,” van Vuuren said. “That doesn’t mean that RCP8.5 was wrong.” Continually updating scenarios to account for new data and understandings, he says, “is just the regular way we do our climate research.”The reasons why RCP8.5 seems to have struck such a nerve on the right stems back to a series of wonky debates among academics that started nearly a decade ago. Two researchers at the University of British Columbia—Justin Ritchie and Hadi Dowlatabadi—published a pair of papers back in 2017 arguing that the modelers relied too heavily on coal, and that extremely high coal usage in RCP8.5 entailed burning through more coal than exists in the world’s recoverable reserves of that resource. Subsequent entries into this debate cautioned against treating RCP8.5 as a “business as usual” outcome when the world looked increasingly on track to warm by roughly 3 rather than 4 or 5 degrees Celsius by 2100.Right-wing think tanks and climate skeptics glommed onto this debate to make a handful of bad-faith arguments that have relatively little to do with the generally good-faith academic discussions about the merits of RCP8.5.
