Countries have pledged to create a global, market-based system to control carbon dioxide emissions from international airline flights by 2020. Under an agreement completed at a gathering of the International Civil Aviation Organization (ICAO) earlier this month, countries will propose the emissions control system in 2016. It is to start operation in 2020, the same year a climate-change treaty now under negotiation at the United Nations is supposed to kick in. The decision by governments under ICAO, the UN aviation agency, is a setback to the European Union’s system to control greenhouse gas emissions from airplanes that take off and land in the EU. The regional program has been under fire by the U.S., China, and other countries since it began on Jan. 1, 2012. The EU suspended it about a year ago after some nations opposing the region’s airline emissions allowance program threatened to retaliate with trade sanctions. EU Climate Action Commissioner Connie Hedegaard says the region will change its system for controlling airline emissions in light of the ICAO deal.