Global greenhouse-gas emission reductions could be achieved in a fair and thrifty way by surprisingly small variations of well-known policies. This is shown by a team of economists in a quantitative study now published in Nature. Differentiated CO2 prices in different countries combined with moderate financial transfers from advanced to developing countries would do the job. These changes would be most efficient in achieving fair burden sharing and at the same time keep overall costs in check, the researchers find. This could solve the epic trilemma to unite cost-efficiency, national sovereignty and fair effort-sharing.