Infant feeding practices have environmental consequences that are largely absent from climate policy discussions. Breastfeeding relies on maternal metabolism and local support systems, whereas commercial milk formula depends on dairy production, industrial processing, packaging, and extensive supply chains. Comparative analyses report higher greenhouse-gas and water burdens for commercial milk formula than for breastfeeding. Globally, commercial milk formula use among infants under 6 months of age adds roughly 5.9-7.5 billion kg of carbon dioxide equivalent (CO2e) annually. Pumping and bottle-feeding add material, electricity, and cleaning-related burdens relative to feeding at the breast, but the magnitude of these impacts is far less than that of commercial milk formula. Climate change and water insecurity can also threaten breastfeeding through heat stress, food insecurity, and disruptions during disasters and emergencies. Moreover, uncontrolled formula donations during upheavals, while well-intended, impede continuation of breastfeeding. Collectively, these pressures can generate a feedback loop: climate shocks undermine breastfeeding, increasing reliance on resource-intensive substitutes that further strain water and energy systems. Recognizing breastfeeding as both a mitigation and resilience issue highlights co-benefits for child health and climate action and points to practical policy levers, including paid maternity leave, workplace lactation protections, responsible marketing of commercial milk formula, and continuity of lactation support during emergencies that are needed to align optimal infant feeding with climate adaptation planning.