Fig. 1: IIASA IAMC database of scenarios in the IPCC Special Report on the Global Warming of 1.5 °C.

Panel a plots the annual CO₂ emissions. Panel b (below a) shows the running sum (or cumulative) CO₂ emissions from 2018. Panel c (bottom right) shows the non-CO₂ radiative forcing for each scenario (dotted lines, right hand axis). Also on panel c are the cumulative non-CO₂ CO₂-fe emissions from 2018 corresponding to each non-CO₂ RF line (solid lines, left-hand axis). The axes of panels b and c are scaled so the cumulative emissions from CO₂ and non-CO₂ are directly comparable. Panel d plots the FaIRv2.0-derived temperature response against the diagnosed cumulative CO₂-fe emissions (solid lines) and against the cumulative CO₂-only emissions (dotted lines). For FaIR temperature response TCR = 1.8 °C, ECS = 3.0 °C. Scenarios are coloured by category in the IAMC database: red for 2 °C-higher, orange for 2 °C-lower and blue for 1.5 °C-compatible. Light blue scenarios in panel c highlight some example non-CO₂ pathways (lower bound, upper bound and a central scenario from 1.5 °C-compatible dark blue plume) with the central light blue scenario (P3 scenario from SR15 SPM.3b) also used in Figs. 2 and 3.