In the United States, approximately 70% of fluid milk carbon footprint occurs on-farm primarily from cows [enteric methane (CH₄)], from manure [CH₄ and nitrous oxide (N₂O)], and from cropland [carbon dioxide (CO₂) and N₂O]. In spite of some methodological inconsistencies attributional life cycle assessments (LCA) have consistently reported farm-gate emissions around 1.00 kg CO₂ equivalent per kg of milk. Variations among farms within a production system are large and often greater than across production systems (conventional, grazing or organic). Dry matter intake is the main driver of daily enteric CH₄ emission. Thus, reduction of enteric CH₄ per kg of milk depends heavily on feed-to-milk conversion efficiency. Consequently, better herd health, increased productive life (decrease culling rate), reduction in replacement herd, and in the long term, genetic selection for feed efficiency are effective practices that lowers milk carbon footprint. Dietary composition (type and level of carbohydrates, fiber, and fat, as well as feed additives) has direct effects on enteric CH₄ and indirect effects on N₂O because dietary crude protein determines manure N content and vulnerability to gaseous N emissions. In the manure management chain, aerobic conditions (e.g., aerated compost) depress CH₄ but stimulate N₂O emission, and the reverse is true for anaerobic manure systems (e.g., liquid storage systems). Mitigation options in the field have focused primarily on reducing the loss of CO₂ (soil organic matter) and reducing N₂O emission. Introductions of perennial crops or winter crops contribute carbon storage in plants and soils. Reduced or no till and the incorporation of organic matter (manure or crop residues) also favor carbon sequestration in soils, but may enhance N₂O emission. Although attributional LCA emphasizes increasing productivity and efficiency of farm (sub-) systems, and recovering energy (e.g., manure bio-digestion) and nutrients, recent consequential (expanded boundaries) LCA has suggested important trade-offs that cannot be ignored if the goal is to reduce actual emissions rather than the carbon foot print of the dairy sector.