Last weekend, former US President Donald Trump took to social media to lash out at a particular climate projection scenario, “RCP8.5,” which paints a picture of a future with extraordinarily high carbon emissions. He declared it “wrong, wrong, wrong,” falsely claiming that the UN’s “top climate committee,” the Intergovernmental Panel on Climate Change (IPCC), had “just admitted” this. This statement quickly became fodder for right-leaning media, who amplified Trump’s misrepresentation of climate science and the IPCC’s role. His pronouncement came on the heels of the release of new emissions scenarios that will inform upcoming IPCC reports. While these newer scenarios no longer include such extreme-high emission pathways as RCP8.5, one of the authors, Dr. Chris Smith, points out a sobering reality: it’s “not possible” to limit global warming to 1.5 degrees Celsius above pre-industrial levels without significant “overshoot.” Another author notes that current projections still put the world on track for a deeply concerning 2.5 to 3 degrees Celsius of warming – a level previously deemed “catastrophic” by the UN. This situation leaves us with a complicated mix of “good” and “bad” news, forcing us to re-evaluate our climate trajectory.
Trump’s social media tirade on May 16th was punctuated by his characteristic inflammatory language, including a derogatory nickname for Democratic politicians. He clearly aimed his criticism at the IPCC, the UN body tasked with assessing climate change science. The crucial point, often missed or deliberately overlooked by those who echoed his claims, is that the IPCC doesn’t create or own climate scenarios; rather, it assesses existing scientific literature, which includes scenarios developed by other groups. The idea that the IPCC would declare any scenario “wrong” is fundamentally misunderstanding its mandate. Yet, media outlets, particularly those with a conservative slant, jumped on Trump’s comments. The New York Post, for example, incorrectly suggested the IPCC had “quietly adjusted” its framework, while the Daily Caller spun a conspiratorial tale about IPCC researchers revising their models. Even more dramatically, a climate-skeptic Australian outlet declared scientists had “quietly scrapped the apocalyptic forecasts that have terrified policymakers and the public.” This wasn’t an isolated incident; the Trump administration had previously targeted RCP8.5 in a 2025 executive order, “Restoring gold-standard science,” alleging that previous administrations had used “highly misleading” scientific information by emphasizing RCP8.5. This attack dovetailed with recommendations from influential right-wing think tanks, like the Heritage Foundation, which in 2023 called for eliminating the US Environmental Protection Agency’s use of “unrealistic climate scenarios, including those based on RCP8.5.” This concerted effort to discredit RCP8.5 highlights a broader political agenda to downplay the urgency of climate action.
To truly grasp the debate, it’s essential to understand what RCP8.5 actually is. These “emissions scenarios” are not crystal balls predicting the future; they’re tools scientists use to explore various potential climate futures based on how global energy and land use might evolve. Therefore, Trump’s assertion that RCP8.5 projections were “wrong, wrong, wrong” fundamentally misunderstands their purpose. RCP8.5, one of four “representative concentration pathways” (RCPs) developed in the early 2010s, was designed to represent the higher end of plausible baseline scenarios – those assuming no climate mitigation policies. The “8.5” refers not to temperature rise, but to “radiative forcing” by 2100, a measure of the Earth’s energy imbalance caused by greenhouse gases. As the highest forcing pathway, RCP8.5 depicted a future of very high emissions and significant warming. When it was first published in 2011, it aimed to capture the 90th percentile of baseline scenarios. The IPCC’s fifth assessment projected a best estimate of 4.3°C warming by 2081-2100 under RCP8.5. Later, the successor scenarios, called “shared socioeconomic pathways” (SSPs), including SSP5-8.5, were used for the IPCC’s sixth assessment, indicating even higher potential warming. The key takeaway is that RCP8.5 was always intended as an extreme, “no-policy” scenario, a benchmark to understand the consequences of inaction, not a probable forecast.
Professor Detlef van Vuuren, a leading figure in emissions scenario development, emphasizes that RCP8.5 was always considered a “low-probability, high-risk scenario.” It wasn’t meant to be a “best-guess” of the future. Yet, a misinterpretation emerged in some research, where RCP8.5 was mistakenly labeled “business as usual,” implying it was the most likely outcome without climate action. This, van Vuuren clarifies, was “incorrect” and “never a likely outcome.” This mischaracterization fueled a heated academic debate. Some argued that such high emissions were becoming increasingly improbable, while others contended that RCP8.5 remained consistent with historical CO2 trends. While global emissions up to the early 2010s did somewhat track RCP8.5, a flattening of emissions growth since then means they haven’t kept pace with the scenario’s sustained increases. In fact, over the past decade, emissions have more closely aligned with RCP4.5, a “medium stabilization” scenario. Critics of RCP8.5 also pointed to its assumptions of a dramatic expansion of coal use and high population growth, which seemed increasingly unrealistic. For example, a 2017 paper argued the “return to coal” envisioned in RCP8.5 would require an unprecedented five-fold increase in global coal use, an “exceptionally unlikely” outcome. However, proponents argued that even if less probable, high-emissions scenarios are vital for understanding high-risk possibilities and potential climate feedbacks that could amplify warming.
As the scientific community prepares for the IPCC’s seventh assessment cycle (AR7), new emissions scenarios are being developed. This process, known as ScenarioMIP, began with brainstorming sessions involving diverse climate research communities. The result is a set of seven new scenarios, replacing the older SSPs and RCPs, named for their greenhouse gas emission levels. Significantly, the authors note that the range of future emissions in these new scenarios “will be smaller.” They explain that the very high emission levels of the former SSP5-8.5 have become “implausible” due to advancements in renewable energy, the emergence of climate policies, and recent emission trends. Conversely, many very low emission trajectories have become “inconsistent with observed trends.” In essence, the combination of technological progress and some – albeit insufficient – climate action has narrowed the spectrum of plausible futures. Dr. Chris Smith describes this as a “narrowed range of potential futures.” While we’ve “ruled out futures at the high end,” importantly, we’ve also “ruled out futures at the low end” – meaning it’s no longer possible to limit warming to 1.5°C without significant “overshoot.” The “good news” is that we’ve eliminated the most extreme high-end possibilities, a consequence of bending the emissions curve. However, the “bad news” is that even the lowest of the new scenarios projects a peak warming of about 1.7°C, and the new “high” scenario projects warming closer to 3.2°C by 2100. This means the world is now on a trajectory of 2.5-3°C of warming, signifying a “significant overshoot” of the 1.5°C target.
Crucially, the IPCC is not the architect of these scenarios, contrary to Trump’s assertions. The development of emissions scenarios is spearheaded by the Coupled Model Intercomparison Project (CMIP), overseen by the World Climate Research Programme. CMIP coordinates global climate modeling centers, asking them to run standardized experiments using fixed sets of future climate scenarios. These scenarios are updated with each new CMIP “phase” to reflect scientific advancements and real-world climate action. CMIP aligns its work with the IPCC’s assessment cycles, providing the model runs that feed into the IPCC’s landmark reports. For example, the upcoming AR7 will use models from CMIP’s seventh phase (CMIP7). While the IPCC is consulted during the CMIP process, its input is no different from any other review comment. Dr. Robert Vautard, co-chair of IPCC AR7 Working Group I, clarifies that the IPCC doesn’t “do or coordinate research” but rather “synthesizes existing knowledge” and reviews climate science literature. He emphasizes that CMIP7 scenarios are just one set among many that the IPCC assesses. In short, the IPCC plays a crucial role in evaluating and presenting climate science, but it does not, and has never, created or dictated the emissions scenarios themselves. These scenarios are the product of a collaborative, evolving scientific endeavor, constantly refined to reflect our best understanding of potential climate futures.