• The United Nations' Intergovernmental Panel on Climate Change has discarded the extreme emissions scenario RCP 8.5, a significant development in climate science that will impact markets, government policy, and education.
• RCP 8.5, a climate scenario representing a future with high greenhouse gas concentrations and significant heat trapping, was widely used but deemed implausible by subsequent data, leading to its retirement by the IPCC.
• The retirement of RCP 8.5 has sparked varied reactions, with some welcoming the change as evidence of effective climate policy, while others argue it remains a relevant tool for understanding future climate impacts despite its decreasing likelihood.

(The Center Square) – The United Nations' Intergovernmental Panel on Climate Change threw out one of its most extreme emissions scenarios last week, a major development in climate science that will likely echo across markets, federal and state government policy, and education.

What is RCP 8.5?

RCP 8.5 is the stuff of climate apocalypse nightmares. RCP stands for Representative Concentration Pathway, a future climate scenario Earth could face by the end of the century if no policies were adopted to address climate change.'Concentration' refers to greenhouse gas concentrations in Earth's atmosphere, and the 8.5 refers to the amount of additional heat those gases would trap by 2100.

RCP 8.5 became the highest-emission climate scenario widely used in both academic research and media coverage over the past decade. But last week, the panel determined that RCP 8.5 described a future that subsequent data has shown to be too implausible to remain a useful benchmark for climate projections.

Why is the panel's decision-making headlined?

The panel's decision was significant because of how influential RCP 8.5 has been, not only within the field of climate science, but within academia, the media, business and government. It became foundational in climate science education, shaped outward-facing climate communication and was sometimes utilized in localized climate-impact modeling.

It influenced corporate climate-risk assessments used by insurance companies, banks and investment firms to evaluate long-term property and infrastructure risks, which can affect insurance costs and investment decisions. It also informed some taxpayer-funded climate planning and policy analysis at the federal level.

Reactions to the IPCC's decision are varied

Some scientists and policy analysts have welcomed the change and said RCP 8.5 was obviously an unreliable benchmark since its inception.

Travis Fisher, director of energy and environmental policy studies at the Cato Institute, believes the warming scenario was based on "implausibly, absurdly ridiculous" assumptions from the start.

"What if we decide to dig up every ounce of coal on planet earth and burn it at the same time? Yeah, what if?" Fisher said in an interview with The Center Square. "This world where we find every hydrocarbon on planet earth and burn it — that [was] the scenario."

Others say the panel's retirement of RCP 8.5 is evidence that climate policy is working.

"Although often slow and incomplete, our efforts to tackle climate change have made a tangible difference," wrote Andrew King, an associate professor in climate science at the University of Melbourne. "[But] the job is far from done. Emissions are at record highs and global warming is speeding up."

Still others say that RCP 8.5 remains a relevant scenario for modeling future climate impacts. In an article titled RCP 8.5 is Fine, Actually, published by the Center for Progressive Reform, the writers contend it is, in fact, a "crucial tool to help us understand the climate impacts that lie ahead — even as the emissions trajectory it represents, fortunately, becomes less likely."

They argue, among other things, that it's possible that lower levels of emissions in other warming scenarios could "lead to temperatures conventionally associated with RCP 8.5" because the Earth's climate sensitivity to greenhouse gas concentrations isn't fully understood, and neither is Earth's carbon cycle.

Climate and emissions modeling is also extremely complex and subject to significant scientific uncertainties.

Where does climate science go from here?

The IPCC also introduced seven new overarching emissions pathways to be used in modeling and projections that are meant to better reflect contemporary conditions and climate policy.

As for how the panel's retirement of the widely used worst-case warming scenario will affect public perceptions of climate science, that remains unclear.

Fisher thinks it may cause some to be less trusting of the panel and other authorities on climate science, but that it's also a good thing for the field as a whole.

"It's gonna basically red pill a bunch of people," Fisher said, but "I think it actually does the world of climate science, a favor by basically hitting reset on the most outlandish claims and getting back to reality."

"There's a history of overstepping and trying to be alarmist and catastrophic, but I think it's a positive thing [they're] correcting it now instead of doubling down on it."