The carbon footprint associated with the ingredients of this dish (1,141 g CO2-eq for the whole recipe) is dramatically lower than that for a comparable dish with beef (13,443 g CO2-eq for the whole recipe) instead of the Portobello mushrooms. The reason for this is that cattle are ruminant animals, so the carbon footprint includes not only all of the feed that goes into raising the animals, but also the methane and nitrous oxide (both potent greenhouse gases) associated with the animals’ metabolism and manure. See below for an ingredient by ingredient breakdown of carbon footprint for the major components of this recipe.