An estimate of the distribution of wetland area and associated CH4 emission is presented for the Last Glacial Maximum (LGM, 18 kyr BP, kiloyear Before Present) and the Pre-Industrial Holocene (PIH, 9000-200 years BP). The wetland source, combined with estimates of the other biogenic sources and sink, yields total source strengths of 120 and 180 Tg CH4/yr for LGM and PIH respectively. These source strengths are shown to be consistent with source estimates inferred from a photochemical model, and point to changes in wetland CH4 source as a major factor driving the atmospheric CH4 increase from LGM to PIH. -Authors