Fig. 5: The spread in steady-state pCO₂ from varying a single model parameter.

Each parameter in Table 1 is shown on the vertical axis (note that n_out and τ are incorporated into Q, see Eq. (10)). The left panel shows an incident flux of S = 1.0S_⊕. The right panel shows an incident flux of S = 0.5S_⊕. For each parameter, we held all other parameters constant at the modern Earth value (see text) and randomly sampled 100 values for the parameter in question from uniform distributions of the ranges given in Table 1. The horizontal extent of the gray shaded region shows the range of possible pCO₂ values when all other parameters are fixed. The thickness of each gray shaded region shows the relative abundance of steady-state planets at that pCO₂. The thickest regions show maximum relative abundance, the thinnest regions show the minimum relative abundance. No surface temperature limits on habitability were imposed for the simulated planets. At low pCO₂, three parameters (f_land, f_bio, and Q) dominate the spread in pCO₂. At higher pCO₂, the temperature- and pCO₂-dependence of continental silicate weathering (T_e and α) are also important.