Integrated scheduling is a powerful way to reduce carbon emission of pickup and delivery because the vehicle loading efficiency can be improved. Our study investigates theoretically the potential carbon emission reduction brought by integrated scheduling, and develops the upper and lower bounds. To demonstrate the practical advantage of carbon emission reduction brought by integrated scheduling, we use the real application of pickup and delivery, i.e., “picking up and delivering customers to airport” (PDCA). Using based-on-set-partitioning formulation, we accurately obtain the minimal carbon emissions of non-integrated scheduling and integrated scheduling. We conclude that integrated scheduling reduces carbon emission by approximate 10.8%. However, the cost in integrated scheduling may be more than before, which causes a company unwilling to accept integrated scheduling. The acceptable integrated scheduling is proposed. We identify the situations under which carbon emission can be efficiently reduced in acceptable integrated scheduling based on the extensive experiments of PDCA.