What are Representative Concentration Pathways (RCPs) and how do they differ from SSPs?

• A. RCPs are radiative forcing trajectories used in climate modeling; SSPs are socio-economic scenarios; modern analyses combine SSPs with RCPs to link futures with forcings.
• B. RCPs are regional climate projections; SSPs are solar activity proxies.
• C. RCPs drive climate models; SSPs drive economic policy;
• D. RCPs and SSPs are two names for the same concept.

Answer: (A)

RCPs describe how the amount of radiative forcing—essentially the energy imbalance caused by greenhouse gases and other factors—evolves over time. They are used as input for climate models to project how the climate responds to different forcing levels, with end-of-century values often expressed in watts per square meter. They’re about the physical pathway the climate system follows, not about why society changes.

SSPs, on the other hand, are narratives of how the world might develop socio-economically—population, economic growth, technology, energy choices, land use, and policies. They don’t specify a climate forcing trajectory themselves; instead, they set the context for emissions and land-use changes that then map onto a given forcing pathway.

In practice, researchers link the two by pairing SSPs with RCPs. This allows exploration of futures where a particular social and economic development path leads to a specific climate forcing outcome, or to examine how different social choices might realize low- or high-forcing futures. That combination is the reason modern analyses discuss both together.

So, the best answer is that RCPs are radiative forcing trajectories used in climate modeling, SSPs are socio-economic scenarios, and modern analyses couple them to connect future social pathways with forcing and climate outcomes.