High latitude wetlands are significant sources of atmospheric methane, with emission rates that are susceptible to effects of climate change. Our data demonstrate that unlike mid-latitude wetlands, methane in northern peatlands is not derived from acetate or C1 compounds. These latter compounds accumulate to high levels with acetate as the primary organic end product of anaerobic decomposition. Acetate is ultimately degraded aerobically to carbon dioxide after diffusion into oxic regions of peat. Therefore, organic precursors destined for methane in mid-latitude wetlands are degraded to carbon dioxide in northern wetlands. A warming-induced initiation of acetoclastic methanogenesis could substantially increase methane production. ¿ 2001 American Geophysical Union