After the first year, we allowed the fire-emitted CH4 (and its influence on
radiative forcing) to decrease with an atmospheric lifetime of 10 years, reflecting
oxidation by OH and other sink processes. Fire-emitted CO2 was removed from the
atmosphere by two sinks: the accumulation of carbon in the recovering post-fire
ecosystem and via ocean exchange. In considering this single fire, we assumed the rest of
the terrestrial biosphere was neither a sink nor a source. Our approach for estimating the
post-fire trajectory of net ecosystem production (NEP) and subsequent carbon
accumulation is described in section 1.3. Ocean uptake of the fire-emitted CO2 pulse was
estimated using an impulse response function from the Joos and Siegenthaler ocean
carbon model as described by Enting et al. (2001). This response function (fig. S3C) was
constructed assuming that the emitted pulse occurred at contemporary CO2 levels and that
fossil fuel emissions continue on a trajectory required for stabilization of atmospheric
CO2 at 650 ppm by 2100 (24). In each year after fire, ocean exchange acted only upon the
component of the fire-emitted CO2 pulse that remained in the atmosphere (that wasn’t
taken up in previous time steps by regrowing vegetation or by ocean exchange).