On the death of RCP8.5

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On the death of RCP8.5<br>We should celebrate progress, but not overstate it

Zeke Hausfather, Glen Peters, and Piers Forster<br>May 18, 2026

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With the release of the new van Vuuren et al 2026 paper on the emissions scenarios that will be used in the upcoming IPCC 7th Assessment Report, the internet has been abuzz with debate over the implications of the formal retirement of the RCP8.5/SSP5-8.5 scenario. The president of the United States even weighed in over the weekend in his own unique style, posting that “the United Nations TOP Climate Committee just admitted that its own projections (RCP8.5) were WRONG! WRONG! WRONG!”.<br>van Vuuren et al justify this move by noting that “the CMIP6 high emission levels (quantified by SSP5-8.5) have become implausible, based on trends in the costs of renewables, the emergence of climate policy and recent emission trends,” citing the paper that we published in Nature back in 2020.

Actual global CO2 emissions (black) compared to different generations of emissions scenarios featured in IPCC reports. Updated by Glen Peters through 2025.<br>Others have pointed out that RCP8.5 was never particularly plausible, and have criticized claims that the move away from using these scenarios reflects actual progress on reducing emissions.<br>So what actually happened here? It turns out that two things can be true at the same time:<br>RCP8.5 (and its successor SSP5-8.5) were designed to be a worst case emissions scenario, not the most likely outcome even in a world that did nothing to address climate change. We were probably never headed to a tripling of global emissions by 2100 (to say nothing of a five-fold increase in coal use), even in the absence of climate policy.

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. The 21st century is now unlikely to see a continued expansion of fossil fuel use globally, with current policy scenarios reflecting relatively flat global emissions going forward.

Beyond business as usual

Emissions scenarios can broadly be categorized as “baseline” scenarios or “mitigation” scenarios. Baselines represent worlds where there are no additional efforts to address climate change (or in some cases turn back the clock to some earlier period and assume no policy after that point), while mitigation scenarios explore concerted efforts to reduce global emissions.<br>When RCP8.5 was first published global emissions were skyrocketing, having increased 30% in just the past decade. Clean energy sources were quite expensive, electric vehicles largely non-existent, and the idea that we would continue to increase our use of coal, oil, and gas through the end of the century was not seen as far-fetched.<br>Even in that context, RCP8.5 was chosen to represent the high end of the baseline scenario range available to the researchers at the time – around the 90th percentile. It was never a likely outcome even in a world that did not address climate change; rather it was always intended to represent a worst case scenario that pushed fossil fuel expansion to the max.<br>There are many other baseline scenarios with lower emissions, which were equally plausible as RCP8.5, even in the absence of climate policy. The original article that published the baselines, shows total CO2 emissions can be as low as RCP4.5 depending on the socioeconomic assumptions and the model used.<br>However, in part due to a breakdown in communication between the energy modeling community that develops the scenarios and the climate science community that uses them, RCP8.5 came to be incorrectly portrayed by many as the most likely “business as usual” scenario.<br>Around a decade ago the scenario started to garner more criticism. Justin Ritchie and Hadi Dowlatabadi published a paper in 2017 questioning whether the extremely high use of coal in RCP8.5 – which envisioned things like turning coal to oil for vehicles when oil reserves ran dry later in the century – was even possible given the world’s recoverable coal reserves. Ritchie and I (Zeke) wrote in 2019 that a 3C world was now “business as usual”, reflecting that:<br>Our business-as-usual projection of 3C of warming – rather than 4 or 5C – is a testament to the progress in global decarbonization over the last few decades. It also reflects the fact that rapid growth in coal use during the 2000s was not necessarily characteristic of longer-term energy use trends. The world has taken concrete steps to move away from coal in the past decade, and this progress should be reflected in our assessment of likely emissions pathways – and their resulting climate impacts – going forward.

In 2020 we published our Nature piece, arguing that we should “stop using the worst-case scenario for climate warming as the most likely outcome”, and that outcomes like RCP8.5 had...