The United Kingdom and France are currently suffering through a heatwave that would be impressive for the middle of summer. It’s May. A heat dome is the culprit. “It’s the same mechanism that has been affecting India for weeks, with temperatures exceeding 45 degrees Celsius (112 degrees Fahrenheit) in some places, and has led to wildfires in Canada in 2021,” noted France24.com. In my neck of the woods, we’ve experienced one of the worst spring droughts on record and with intermittent extreme bursts of rainfall that shut down major interstates in Atlanta. Yet, a recent discussion within the scientific community has mistakenly created a false narrative for the public. Let’s use a simple analogy to explain the confusion and why climate change is still a major threat to society.
The Worst-Case Climate Scenario Retired But There Is A “But”
“I’ve got to say that I’m really disappointed in the recent discourse surrounding the RCP8.5 scenario,” wrote climate expert Daniel Swain on his LinkedIn page. “The lack of context and understanding is something I expected from the usual suspects, but it’s frustrating to see such bad takes from people and outlets who should know better,” he went on to say. What is he talking about?
Recently, a UN panel of scientists essentially said the RCP8.5 scenario, often called the “worst-case” scenario, is likely not going to be realized. What’s that? Swain refers to it as the “burn all the coal” scenario, which was likely never going to happen anyhow. I will circle back to this later, but I need to bring scenarios into the chat.
What Are Scenarios?
To project future climate change, there are many things to consider including the climate system itself, amount of greenhouse gases, various sensitivities, population assumptions, mitigation activities, land use, and so on. “To try and capture a range of possible future emissions, energy system modellers have used integrated assessment models (IAMs) that simulate both future energy technologies and emissions,” wrote Zeke Hausfather. His RCP8.5 scenario explainer went on to say, “These produce emissions scenarios that are then used by scientists to run complex climate models that simulate how the climate might change in the future.” RCP stands for Representative Concentration Pathway and represents a top-of-the atmosphere forcing of 8.5 watts per meter squared. Yeah, that’s pretty jargony stuff so we will shelve it for now.
“RCP8.5 was intended to be a ‘very high baseline emission scenario representing the 90th percentile of no-policy baseline scenarios available at the time,” said Hausfather. “The creators of RCP8.5 had not intended it to represent the most likely ’business as usual’ outcome, emphasising that ‘no likelihood or preference is attached’ to any of the specific scenarios,” wrote Hausfather in 2019. Though never the likely scenario, here’s where the conflict and confusion lies.
Many scholarly research papers and media outlets often mention RCP8.5 without the proper context. I remember a conversation many years ago with my friend and colleague, former Congressman Bob Inglis. Inglis, who is Executive Director of republicEn.org, told me that it is good conservative principle to understand all of the range of possible outcomes, and that’s absolutely still the case. There are many other scenarios that are really bad for the planet and society. Unfortunately, all of this “scenario” stuff is meaningful in the research and policy world but can quickly be taken out of context in the public sphere. That’s why I also cringed when I saw some of the headlines about the UN panel announcement.
Swain quibbles with the narrative that the RCP8.5 scenario has been overturned. “It’s still possible the Earth system is more sensitive to a given level of greenhouse gase increase/aerosol decrease than previously assumed, and, thus, could warm more than indicated in historial IPCC scenarios even with a lesser degree of GHG increase,” Swain argued and suggested recent evidence supports this claim.
A Simple Yet Imperfect Analogy
By the way, Shared Socioeconomic Pathways have also emerged. SSPs offer a more expansive view. Candidly, criticism of narratives anchored solely on the RCP8.5 scenario without context is fair. I would often try, possibly failing at times, to frame my discourse with context and would often ask my students what is problematic about risk communication with only one scenario. Swain, Inglis, and Hausfather are all saying the same thing. Using a range of scenarios, including the “worst-case,” is scientifically valid and informative if communicated with the proper context and constraint.
According to Swain, we are probably on an upper mid-range gas emission trajectory through the rest of the decade. This would likely fall between RCP4.5 and RCP6 scenarios. Those aren’t great folks. For me, a simple analogy comes to mind to explain this in a way that makes sense. It’s not perfect, however. Let’s say a person goes out drinking at the bar. There are a range of outcomes that we could predict a few hours later. They include:
- He just drinks soda all night and watches the game. Drives home safely.
- He has a couple of beers but remains below the legal limit and gets home safely.
- He has 4 to 5 beers and is above the legal limit and takes a risky drive home or calls rideshare.
- He has 10 beers and drives home under extreme impairment or calls a rideshare.
- He has 10 beers and starts a bar fight that results in multiple injuries and several arrests.
- He drinks all of the beers at the bar and in the cooler too with expected dire outcomes.
What the UN panel did, from an analogy standpoint, is take the last scenario off the table. He was never going to drink all of the beer, but there are still very problematic scenarios on the table. Understanding all of these scenarios and overlooked ones helps inform the decision space for the patron, bar owner, and the local jurisdiction.
Extreme weather, sea level, agricultural productivity, infrastructure vulnerability, health outcomes and energy-water systems are exhibiting impacts of climate change already and that will likely accelerate. Taking the RCP8.5 scenario off the table is certainly good news. “Rapid declines in clean energy costs have bent the curve of future emissions downward, with new scenarios designed to reflect current policies notably lower than most baseline scenarios in the literature,” wrote Hausfather, Glen Peters, and Piers Forster in the aftermath of the RCP8.5 bruhaha. The very irony of this discussion is that climate change urgency has likely helped move the needle towards cleaner energy and removal of the RCP8.5.
To carry my “bar” analogy forward, it’s akin to slowly removing beer from the bar or adopting a policy of one glass of water for every beer up to a certain limit. Hausfather, Peters, and Forster went on to write, “The brutal math of climate change is this: as long as CO2 emissions remain above zero, the world will continue to warm. The medium scenario ends up closer to 3.7 degrees Celsius by 2150, while the high scenario ends up more or less matching the warming in the old RCP8.5 scenario despite an assumption of flattening or modestly declining emissions after 2100.”
We still have work to do in order to slow climate change and its impacts. We also still have work to do in properly conveying the story and context for the public. I never really liked the term “worst-case” scenario. It conveys that there is only a singular outcome that is really bad. Actually, there are many out there lurking.
