Figure 3. Summary of the contributions to the glacial to inter-glacial CH₄ budget as modelled in this work and in previous studies.

V: Valdes et al.⁸, K: Kaplan et al.⁷,¹⁴, L: Levine et al.¹⁵. T: Thonicke et al.²⁹ and S: Singarayer et al.¹⁰. The contributions from individual sources are calculated assuming no change in lifetime, while the contributions from sinks are calculated with constant source terms. The total concentration changes take account of both source and sink changes. The separate contributions to the change in chemical lifetime of CH₄ are quantified for the low-fire scenario here. The non-CH₄ term will be smaller for the standard fire and standard+LGM humans fire scenarios. The uncertainty range in each of the ‘Net' values, encompasses whether or not peatlands are considered. Details of these calculations are given in Supplementary Table 2.