This paper presents a method to assess the key performance indicators of aircraft designed for minimum direct operating cost and aircraft designed for minimum global-warming impact. The method comprises a multidisciplinary aircraft optimization algorithm capable of changing wing, engine and mission design variables while including constraints on flight and field performance. The presented methodology uses traditional Class-I methods augmented with dedicated Class-II models to increase the sensitivity of the performance indicators to relevant design variables. The global-warming impact is measured through the average temperature response caused by several emission species, including CO2, NOx and contrail formation, over a prolonged period of one hundred years. The analysis routines are verified against experimental data or higher-order methods. The design algorithm is subsequently applied to a single-aisle, medium-range aircraft, demonstrating that a 45% reduction in average temperature response can be achieved by flying at 8.64 km and Mach 0.61, and by reducing the engine overall pressure ratio to 34 when compared to an aircraft optimized for minimal operating costs or fuel burn. However, if the total productivity of the aircraft fleet is to be maintained, the potential reduction shrinks to 38%.