Revision of SSP5-8.5: From Baseline to Outlier (Van Vuuren et al., 2026)
In 2026, a team led by Detlef van Vuuren published a reassessment of the high-end IPCC emission scenarios in the journal Geoscientific Model Development. The study concludes that SSP5-8.5 — formerly used as a plausible “business-as-usual” baseline — should be reclassified as a low-probability outlier rather than a central planning scenario.
Background: What Is SSP5-8.5?
The Shared Socioeconomic Pathways (SSPs) are a set of emission scenarios developed for the IPCC Sixth Assessment Report (AR6). SSP5-8.5 describes a world with very high fossil fuel consumption, resulting in a radiative forcing of 8.5 W/m² by 2100. It is roughly equivalent to the older RCP8.5 scenario used in AR5.
SSP5-8.5 was included in IPCC reports as the upper bound of the scenario range — not as a prediction, but as a stress test for worst-case climate outcomes. In practice, however, SSP5-8.5 became widely used in scientific literature and national policy assessments as a reference scenario for high-end projections.
The 2026 Revision
Van Vuuren et al. (2026) argue that the fossil fuel combustion levels required to reach SSP5-8.5 have become increasingly implausible given observed trends:
| Indicator | SSP5-8.5 assumption | Observed trend (2026) |
|---|---|---|
| Global CO₂ emissions by 2100 | ~128 Gt CO₂/yr | New high estimate: ~71 Gt CO₂/yr |
| Coal use | Massive increase | Declining in most world regions |
| Renewable energy share | Slow growth | Rapid, faster-than-projected expansion |
The authors propose a revised scenario range in which the new high-end pathway reflects roughly 71 Gt CO₂/yr by 2100 — significantly below the SSP5-8.5 level — and corresponds to a global mean temperature increase of approximately 2–3.5 °C by 2100, compared to the 4–6 °C range associated with SSP5-8.5.
The revision does not eliminate SSP5-8.5 from the IPCC scenario library, but reframes it as a low-probability sensitivity case rather than a plausible baseline.
Implications for National Climate Projections
The revision has direct relevance for national climate adaptation policies that were built on SSP5-8.5 as a planning benchmark. A prominent example is the Dutch KNMI ’23 climate scenario set, published by the Royal Netherlands Meteorological Institute in 2023.
The KNMI ’23 scenarios include four pathways (G, W, H, WH), of which the highest — scenario H — is based on SSP5-8.5. Scenario H projects:
- A global mean temperature increase of 4.9 °C by 2100
- Sea level rise of 59–124 cm along the Dutch coast by 2100
As of mid-2026, KNMI has indicated it will not update its national scenarios until the next IPCC Assessment Report cycle. The KNMI ’23 scenarios therefore continue to include SSP5-8.5 as a high-end planning scenario, despite the Van Vuuren et al. revision.
Scientific Context
The debate around SSP5-8.5 predates the 2026 paper. Critiques of its use as a default scenario were published as early as 2021, with researchers including Zeke Hausfather and Glen Peters arguing in Nature that the scenario family was being “misused” in the literature by being treated as a prediction rather than an extreme case. Proponents of retaining high-end scenarios argue that the low-probability, high-impact nature of worst-case outcomes justifies their continued use in risk assessments and adaptation planning.
The Van Vuuren et al. (2026) paper contributes quantitative updated bounds to this ongoing discussion.
Video
The following lecture by Detlef van Vuuren discusses the background and implications of the scenario revision:
References
- Van Vuuren, D. et al. (2026). Revised emission scenarios for the IPCC. Geoscientific Model Development, 19, 2627. https://doi.org/10.5194/gmd-19-2627-2026
- Hausfather, Z. & Peters, G.P. (2020). Emissions — the ‘business as usual’ story is misleading. Nature, 577, 618–620. https://doi.org/10.1038/d41586-020-00177-3
- KNMI (2023). KNMI Klimaatscenario’s 2023. Royal Netherlands Meteorological Institute. https://www.knmi.nl/klimaatscenarios
- Klimaatgek.nl (2026). KNMI zit op zijn handen. https://klimaatgek.nl/wordpress/2026/05/08/knmi-zit-op-zijn-handen/
- Klimaatfeiten.net (2026). Van rampscenario naar bandbreedte: wat de nieuwste klimaatmodellen ons wel en niet vertellen. https://klimaatfeiten.net/2026/05/05/van-rampscenario-naar-bandbreedte-wat-de-nieuwste-klimaatmodellen-ons-wel-en-niet-vertellen/