Change in surface temperature in K; in atmospheric height at ToA (~0.01 Pa) in km; and in surface volume mixing ratio (vmr) of H₂O, O₂, CO, and CH₄ with decreasing concentrations of H₂ for scenarios with low (blue lines), medium (green lines), and high CH₄ scenarios. The concentrations of CO₂ corresponding to H₂ vmrs of 0.75,0.5, 0.25, and 0.0 are shown in green on the top x-axis for the medium CH₄ scenarios. The colored dots represent the ten individual main scenarios described in Table 3. The dashed black line shows T = 273 K. The gray shaded region represents the limits of combustion for H₂-CO₂ and H₂ -O₂ gas mixtures (see Grenfell et al. 2018). The assumed surface mixing ratios of H₂ and CO₂ for the main scenarios 5–8 are at the edge of the H₂-CO₂ combustion limit.