SSP scenarios are the framework behind every modern climate projection. Introduced in IPCC AR6, Shared Socioeconomic Pathways (SSPs) define five possible futures for global development, energy use, and emissions policy. Each SSP scenario produces different warming outcomes, which in turn drive different projections for every climate hazard from heat waves to sea level rise.
Understanding SSP scenarios is essential for interpreting climate risk data, meeting TCFD disclosure requirements, and making informed decisions about which future to plan for. The choice of scenario determines the severity of projected impacts at every location in a climate risk assessment.
What Are SSP Scenarios?
SSP scenarios combine two elements: a socioeconomic narrative (the SSP number) and a radiative forcing level (the number after the dash). Together, they describe both how the world develops and how much warming results.
The socioeconomic narratives range from SSP1 (sustainability, strong international cooperation) through SSP5 (fossil-fueled economic growth, minimal climate policy). Each narrative describes different assumptions about population growth, economic development, energy systems, land use, and governance that influence greenhouse gas emissions.
The radiative forcing number represents the additional energy trapped in Earth’s atmosphere by 2100, measured in watts per square meter (W/m2). Higher forcing means more warming. SSP1-2.6 produces 2.6 W/m2 of forcing, while SSP5-8.5 produces 8.5 W/m2.
CMIP6 climate models use these SSP scenarios as inputs to generate global projections for temperature, precipitation, wind, and other variables. These projections feed directly into climate scenario analysis for risk assessment and disclosure.
The Five SSP Scenarios Compared
| Scenario | Narrative | Forcing | Warming by 2100 | CO2 Trajectory |
|---|---|---|---|---|
| SSP1-1.9 | Sustainability (very low) | 1.9 W/m2 | ~1.4 C | Net-zero by 2050 |
| SSP1-2.6 | Sustainability (low) | 2.6 W/m2 | ~1.8 C | Peaks ~2025, declines |
| SSP2-4.5 | Middle of the Road | 4.5 W/m2 | ~2.7 C | Peaks ~2050, then declines |
| SSP3-7.0 | Regional Rivalry | 7.0 W/m2 | ~3.6 C | Doubles by 2100 |
| SSP5-8.5 | Fossil-Fueled Development | 8.5 W/m2 | ~4.4 C | Continuous increase through 2100 |
SSP1: The Sustainability Pathway
SSP1 describes a world that shifts rapidly toward sustainability. International cooperation strengthens, investment flows to clean energy, and consumption patterns become less resource-intensive. Population growth slows, education levels rise globally, and technology development focuses on green solutions.
SSP1-2.6 produces approximately 1.8 degrees Celsius of warming by 2100, roughly consistent with the Paris Agreement goal of limiting warming to well below 2 degrees. SSP1-1.9 is the most ambitious variant, achieving net-zero CO2 emissions by 2050 and limiting warming to approximately 1.4 degrees.
For risk assessment, SSP1 scenarios represent the lower bound of projected climate impacts. Even under these optimistic pathways, significant warming is already committed from historical emissions, so climate hazards still increase relative to today.
SSP2: Middle of the Road
SSP2-4.5 is the most widely used SSP scenario in climate risk assessments because it represents a plausible continuation of current trends. Socioeconomic development follows historical patterns, climate mitigation efforts proceed unevenly, and emissions peak around 2050 before declining.
Warming of approximately 2.7 degrees Celsius by 2100 means substantially greater impacts than SSP1: more intense heat waves, higher flood risk from extreme precipitation, and accelerated sea level rise. Most organizations use SSP2-4.5 as their central planning scenario because it avoids both the optimism of SSP1 and the extremes of SSP5.
NASA’s NEX-GDDP-CMIP6 dataset, the primary source for climate projections used in physical climate risk assessments, provides projections under SSP2-4.5 alongside SSP5-8.5.
SSP3 and SSP5: High-Emission Pathways
SSP3-7.0 (Regional Rivalry) describes a fragmented world where countries prioritize national security over international cooperation. Economic growth is uneven, inequality increases, and climate mitigation stalls. CO2 concentrations roughly double by 2100, producing 3.6 degrees of warming.
SSP5-8.5 (Fossil-Fueled Development) represents the highest emission pathway. High economic growth driven by fossil fuel energy, minimal climate policy, and rapid resource extraction push warming to 4.4 degrees by 2100. While some researchers debate whether SSP5-8.5 remains plausible given recent clean energy trends, it serves as the standard stress test scenario in climate risk assessments.
TCFD recommendations explicitly call for analysis under at least two scenarios, typically SSP2-4.5 and SSP5-8.5, to bracket the range of possible outcomes. Organizations reporting under TCFD should assess their exposure under both pathways.
Which SSP Scenario Is Most Likely?
Current global emission trends track closest to SSP2-4.5, making it the most widely used central planning scenario. Global greenhouse gas emissions have continued rising but at a slower rate than SSP5-8.5 assumes, largely because renewable energy costs have fallen faster than any SSP pathway anticipated. Solar capacity alone grew 50% year-over-year in 2023 and 2024.
The IPCC AR6 Working Group III concluded that SSP5-8.5 is increasingly unlikely as a baseline outcome, though it remains valuable as a high-end stress test for risk management. Nationally Determined Contributions (NDCs) under the Paris Agreement, if fully implemented, point toward warming outcomes between SSP2-4.5 and SSP3-7.0, roughly 2.4 to 2.8 degrees by 2100.
No single SSP scenario can be called “most likely” because future emissions depend on policy decisions, technological breakthroughs, and economic shifts that have not yet occurred. What matters for risk assessment is bracketing the range. Running analysis under both SSP2-4.5 (the planning scenario) and SSP5-8.5 (the stress test) reveals which assets and locations are vulnerable under moderate warming and which face severe exposure only under extreme conditions. The gap between the two scenarios tells risk managers where adaptive capacity matters most.
For organizations conducting TCFD-aligned assessments, pairing these two scenarios satisfies the recommendation to analyze “a 2 degrees or lower scenario” alongside a higher-emission pathway. Most climate risk platforms, including Continuuiti, default to this SSP2 + SSP5 pairing for exactly this reason.
How SSP Scenarios Are Used in Risk Assessment
SSP scenarios serve as inputs to CMIP6 climate models, which generate the temperature, precipitation, and wind projections that feed every downstream climate risk calculation. The choice of SSP scenario determines the severity of projected hazards.
In practice, most climate risk assessments run two SSP scenarios in parallel. SSP2-4.5 provides the central estimate for planning and investment decisions. SSP5-8.5 provides the stress test that reveals which locations and assets are most vulnerable under severe warming.
The difference between scenarios grows over time. Through 2030, SSP2-4.5 and SSP5-8.5 produce nearly identical projections because the climate system responds slowly to emission changes. By 2050, the divergence becomes meaningful. By 2100, the gap is dramatic: the difference between 2.7 degrees and 4.4 degrees of warming translates to vastly different flood frequencies, wildfire risk levels, and heat stress exposure.
SSP Scenarios vs RCP Scenarios
SSP scenarios replaced RCP (Representative Concentration Pathway) scenarios as the standard framework for climate projections in IPCC AR6. While RCPs defined only the radiative forcing pathway, SSP scenarios add socioeconomic context that explains how and why emissions reach a given level.
The forcing levels map approximately: RCP 2.6 aligns with SSP1-2.6, RCP 4.5 with SSP2-4.5, and RCP 8.5 with SSP5-8.5. However, the underlying model generations differ: RCPs used CMIP5 models while SSPs use the newer CMIP6 models, which generally project slightly higher climate sensitivity. For a detailed comparison, see our guide to RCP scenarios.
Frequently Asked Questions
What are SSP scenarios?
SSP scenarios (Shared Socioeconomic Pathways) are frameworks used in IPCC AR6 that combine socioeconomic narratives with radiative forcing levels to project future climate conditions. There are five main pathways (SSP1 through SSP5) representing different assumptions about global development, energy use, and climate policy, producing warming outcomes ranging from 1.4 to 4.4 degrees Celsius by 2100.
What is the difference between SSP2-4.5 and SSP5-8.5?
SSP2-4.5 represents a middle-of-the-road pathway where emissions peak around 2050 and warming reaches approximately 2.7 degrees Celsius by 2100. SSP5-8.5 represents fossil-fueled development where emissions continue rising, producing 4.4 degrees of warming. Through 2030, both scenarios produce similar projections, but they diverge significantly after 2040.
Which SSP scenario is most likely?
Most climate scientists consider SSP2-4.5 the closest to current global emission trends, making it the most commonly used central planning scenario. SSP5-8.5 is increasingly viewed as a high-end stress test rather than a likely outcome, given the rapid growth of renewable energy. However, no single scenario can be called most likely because future emissions depend on policy decisions not yet made.
How do SSP scenarios differ from RCP scenarios?
SSP scenarios replaced RCPs in IPCC AR6. RCPs defined only radiative forcing pathways (the physical outcome), while SSPs add socioeconomic narratives explaining how emissions reach that level. SSPs also use newer CMIP6 climate models, which project slightly higher climate sensitivity than the CMIP5 models used with RCPs.
Why do climate risk assessments use two SSP scenarios?
Using two scenarios (typically SSP2-4.5 and SSP5-8.5) brackets the range of plausible outcomes. SSP2-4.5 provides the central planning estimate, while SSP5-8.5 serves as a stress test. TCFD recommendations explicitly require multi-scenario analysis. Comparing results across scenarios reveals which locations shift from moderate to severe risk under higher warming.
Conclusion
SSP scenarios provide the foundation for every modern climate projection and risk assessment. From SSP1-1.9 at 1.4 degrees to SSP5-8.5 at 4.4 degrees, these pathways define the range of futures that organizations must plan for. Understanding what each SSP scenario means and how they differ is the first step toward interpreting climate risk data and building a credible scenario analysis for disclosure and decision-making.
