“…Methane emissions from hard-to-mitigate sources, such as enteric fermentation, are very large (Rogelj et al, 2015;Reisinger & Clark, 2018), too important to ignore as intractable. For example, high methane mole fractions, often 10-100 ppm can occur in air around feed lots (Figure 19), cattle pens (Grainger et al, 2007), manure heaps, agricultural biodigesters (Flesch et al, 2011), and near active faces of landfills (Riddick et al, 2017;Zazzeri et al, 2015). Methane yield from manure is highly variable, depending on the diet fed to the cattle (Amon et al, 2007).…”