At next week's Group of 20 summit in Antalya, Turkey, world leaders must commit to cutting fossil-fuel subsidies. In 2009, they pledged to do so. Research by the Overseas Development Institute and Oil Change International shows that G-20 governments pump $452 billion annually into the exploration for and production of fossil fuels. Three-quarters of known reserves of oil, natural gas and coal have to stay in the ground if climate change is to be avoided, so this use of public funds is calamitous.

Governments cannot ignore the rising health costs of air pollution, the falling returns on fossil-fuel exploration and the rapid emergence of alternatives, from low-cost solar energy to electric vehicles, that make low-carbon energy systems the smart investment choice. Some governments have acted to rein in highly subsidized fossil-fuel production, but much more has to be done by leading economies.

Ahead of the Paris summit, a timetable for action on subsidies would restore the credibility of the G-20's pledge and send a clear message that the largest economies in the world are willing to take action to meet the challenge of climate change.

Jeffrey Sachs , New York

The writer is director of the Earth Institute at Columbia University and director of the U.N. Millennium Project.

Fan Gang , Beijing

The writer is director of China's National Economic Research Institute.