Shared Socioeconomic Pathways
The Shared Socioeconomic Pathways (SSPs) are five storylines of how society, the economy and technology could develop over the 21st century: population, economic growth, education, urbanisation and technological change, without any new climate policy (O’Neill et al., 2017). Combined with a level of climate forcing, they define the emission scenarios that the climate models of CMIP6 simulate for the IPCC’s sixth assessment report (AR6).
The five storylines
Section titled “The five storylines”Each storyline makes cutting emissions, adapting to climate change, or both, easier or harder.
| SSP | Storyline | Challenge to cut emissions | Challenge to adapt |
|---|---|---|---|
| SSP1 | Sustainability | low | low |
| SSP2 | Middle of the road | medium | medium |
| SSP3 | Regional rivalry | high | high |
| SSP4 | Inequality | low | high |
| SSP5 | Fossil-fuelled development | high | low |
How the scenarios are named
Section titled “How the scenarios are named”A scenario name joins a storyline and a forcing level. In SSP2-4.5, “SSP2” is the middle-of-the-road storyline and “4.5” the radiative forcing reached in 2100, 4.5 W/m². The forcing levels of the Representative Concentration Pathways of the previous assessment were kept, so SSP2-4.5 and RCP4.5 reach the same forcing, and new levels were added (O’Neill et al., 2016).
Table 1. The five core scenarios of AR6 and the warming they imply: global surface temperature in 2081–2100 relative to 1850–1900, best estimate and assessed range (IPCC, 2021, Table SPM.1).
| Scenario | Emissions | Warming by 2081–2100 |
|---|---|---|
| SSP1-1.9 | very low | 1.4 °C (1.0 to 1.8) |
| SSP1-2.6 | low | 1.8 °C (1.3 to 2.4) |
| SSP2-4.5 | intermediate | 2.7 °C (2.1 to 3.5) |
| SSP3-7.0 | high | 3.6 °C (2.8 to 4.6) |
| SSP5-8.5 | very high | 4.4 °C (3.3 to 5.7) |
The scenarios in our datasets
Section titled “The scenarios in our datasets”Our climate projections use three scenarios: SSP1-2.6 (with climate policy), SSP2-4.5 (intermediate) and SSP5-8.5 (without climate policy), from low to very high emissions. To choose among them, see Which scenario should I use? For how the SSPs relate to the RCPs, see What’s the difference between RCPs and SSPs?
References
Section titled “References”- IPCC (2021). Summary for Policymakers. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 3–32). Cambridge University Press. https://doi.org/10.1017/9781009157896.001
- O’Neill, B. C., Kriegler, E., Ebi, K. L., Kemp-Benedict, E., Riahi, K., Rothman, D. S., et al. (2017). The roads ahead: narratives for shared socioeconomic pathways describing world futures in the 21st century. Global Environmental Change, 42, 169–180. https://doi.org/10.1016/j.gloenvcha.2015.01.004
- O’Neill, B. C., Tebaldi, C., van Vuuren, D. P., Eyring, V., Friedlingstein, P., Hurtt, G., et al. (2016). The Scenario Model Intercomparison Project (ScenarioMIP) for CMIP6. Geoscientific Model Development, 9, 3461–3482. https://doi.org/10.5194/gmd-9-3461-2016