A1b

A1B, sometimes written A1b, is a climate-change scenario designation that originated with the IPCC’s Special Report on Emissions Scenarios (SRES) published in 2000. It is part of the A1 family, which describes a future world characterized by rapid economic growth and globalization, with technology advancing quickly and population rising toward the mid‑century before stabilizing.

A1B specifies a balanced or intermediate mix of energy sources, with no single source dominating the global energy supply. This contrasts with other A1 sub-scenarios such as A1FI (fossil-fuel‑intensive) and A1T (predominantly non‑fossil energy). The intent of A1B is to reflect a plausible path where energy demand is met through a diverse mix of fossil fuels, nuclear, and renewables, along with improvements in efficiency.

In climate modelling, A1B was used to drive simulations within the CMIP3 framework and served as a common reference scenario for evaluating potential climate impacts under a mid‑range energy‑mix assumption. Outputs associated with A1B inform projections of global temperature rise, precipitation patterns, and other climate variables, enabling comparisons across sectors and regions.

Following the SRES, the IPCC and the broader research community gradually moved to different scenario frameworks. The A1 family, including A1B, is now largely superseded by the Representative Concentration Pathways (RCPs) used in CMIP5 and the Shared Socioeconomic Pathways (SSPs) used in CMIP6. Nevertheless, A1B remains a frequently cited historical reference in retrospective analyses and in studies that align with older modelling conventions.