Mark Rasmussen's letter (October 2009 Microbe, p. 437) does a creditable job of clarifying the issue of the ruminant contribution to global methane emissions. But in doing so he inadvertently offers up an even larger falsehood than the one he is correcting: that “the carbon dioxide emitted by ruminants contributes as much or more towards global warming than the methane expelled by these animals.” This is a confusion of gross and net fluxes. On an annual basis the CO2 emitted by animals is about equal to the CO2 taken up by the plants they consume, and net emissions are zero to a very good first approximation. Only land use change associated, for example, with conversion of forest to pasture constitutes a net source of atmospheric CO2.