Abstract
Abstract. We investigate the changes in terrestrial natural methane emissions between the Last Glacial Maximum (LGM) and preindustrial (PI) periods by performing time-slice experiments with a methane-enabled version of MPI-ESM, the Max Planck Institute Earth System Model. We consider all natural sources of methane except for emissions from wild animals and geological sources, i.e. emissions from wetlands, fires, and termites. Changes are dominated by changes in tropical wetland emissions, with mid-to-high-latitude wetlands playing a secondary role, and all other natural sources being of minor importance. The emissions are determined by the interplay of vegetation productivity, a function of CO2 and temperature; source area size, affected by sea level and ice sheet extent; and the state of the West African monsoon, with increased emissions from northern Africa during strong monsoon phases. We show that it is possible to explain the difference in atmospheric methane between LGM and PI purely by changes in emissions. As emissions more than double between LGM and PI, changes in the atmospheric lifetime of CH4, as proposed in other studies, are not required.
Highlights
The atmospheric concentration of methane underwent major changes in the time between the last glacial maximum (LGM) and preindustrial (PI) periods
We investigate the changes in terrestrial natural methane emissions between the Last Glacial Maximum (LGM) and preindustrial (PI) periods by performing timeslice experiments with a methane-enabled version of MPIESM, the Max Planck Institute Earth System Model
We assume that this is due to an overestimate of the West African monsoon and its impact on African methane emissions, as a general reduction in the West African monsoon would lead to decreases in TRO emissions for 15, 10, and 5 ka, bringing model results more in line with the implied emissions determined from ice core CH4. This is speculative at this point and would require further experiments. In this assessment we considered all natural emissions of methane, with the exception of emissions from wild animals and geological sources
Summary
The atmospheric concentration of methane underwent major changes in the time between the last glacial maximum (LGM) and preindustrial (PI) periods. Between LGM and 10 ka (before 1950 CE) atmospheric CH4, as reconstructed from ice cores, nearly doubled from ∼ 380 ppb at LGM to 695 ppb at 10 ka (Köhler et al, 2017), with very rapid concentration changes of about 150 ppb occurring during the transitions from the Older Dryas to the Bølling–Allerød (BA), from the BA to the Younger Dryas (YD), and from the YD to the Preboreal (PB) or early Holocene (Fig. 1). The change in methane between LGM and PI has been investigated in a number of studies. Some have used box models to explain the methane changes observed in ice cores
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