# Emissions Scenarios Climate projections cannot predict the future, because the largest single factor in how much the planet warms is a choice not yet made: how much greenhouse gas humanity emits. Emissions scenarios are the standardized "what if" pathways that resolve this. A model is run under each scenario, and the results describe the climate that would follow *if* the world took that path. Confusing a scenario with a prediction is one of the most common errors in public climate discussion, made innocently by readers and deliberately by deniers. ## RCPs and SSPs The framework used since 2014 is the Representative Concentration Pathways (RCPs), labeled by the radiative forcing they reach by 2100 — RCP2.6 (aggressive mitigation), RCP4.5 and RCP6.0 (intermediate), and RCP8.5 (very high emissions). The more recent Shared Socioeconomic Pathways (SSPs) pair each emissions level with a story about how society develops — population, economic growth, energy choices, and international cooperation — so that the physical and the social futures are coupled. An SSP label like SSP2-4.5 names both a development story (SSP2, "middle of the road") and a forcing target (4.5 W/m²). ## The RCP8.5 Controversy The highest scenario, RCP8.5, became the center of a genuine scientific debate. It was designed as a deliberately extreme high-end case — useful for stress-testing — assuming heavy reliance on coal through 2100. For years it was widely, and misleadingly, labeled "business as usual," which made many impact studies sound like forecasts of the most likely future rather than of a worst case. As renewable energy costs collapsed and coal use plateaued, researchers argued RCP8.5 had become implausible as a central expectation. The episode cuts both ways in the politics: deniers cite it as proof that "alarmist" science exaggerates, while climate scientists note that the correction came from within the field through normal self-scrutiny — and that lower scenarios still entail serious harm. Current policies point toward something like 2.5–3°C of warming, better than RCP8.5 but far above the Paris targets. ## Why Scenarios Matter Politically Scenarios make explicit that the climate future is contingent on policy, which is exactly why the [[Energy Transition Politics]] fight matters: the difference between a high and a low pathway is the difference between manageable disruption and catastrophe. They also expose a rhetorical trap — opponents sometimes attack the high scenario to discredit the whole enterprise, or cite the low scenario to argue the problem will solve itself, when both are conditional branches, not forecasts. ## Connections Scenarios are the inputs that [[Climate Models]] turn into projected warming, and they are coordinated through [[The IPCC]] assessment process. Which scenario the world follows is decided in the arena of [[Energy Transition Politics]]. For the field overview, see [[Climate Science]].