Second-hand smartphones reduce carbon emissions, yet shorter use times limit actual gains

Product reuse advances circular economy by reducing material demand. However, environmental assessments often assume reused products fully replace new ones, or they overlook market changes and shortened lifespans driven by resale and repurchase opportunities. This study presents an empirically based analysis of the second-hand smartphone market and its cumulative effects on manufacturing demand and carbon emissions. Integrating consumer survey data and product lifetime estimates in a stock-and-flow model, we find that in the United States, each second-hand transaction currently extends smartphone use time by 40%, displaces 0.40 new devices, and that circular consumption results in a 34% lower annual carbon footprint. With 25% of consumers purchasing used phones, production demand and carbon emissions are lowered by 15% and 14%, respectively. Yet, shortened use times offset nearly half the potential gains. If reuse became the norm, manufacturing demand could decline by one-third, revealing both the promise and the limits of reuse. Circular devices extend use by 40% and cut individual carbon footprint by 34%. A stock-and-flow model using survey data and lifetime estimates shows that at 25% adoption, manufacturing demand and emissions dropped 15% and 14%, and by one-third if reuse becomes the norm.