A UN panel has proposed long-sought greenhouse gas emissions standards for airliners and cargo planes. The International Civil Aviation Organization (ICAO) said the agreement reached by the agency’s environmental panel requires new aircraft designs meet the standards beginning in 2020, and that designs already in production comply by 2023. There is also a cutoff date of 2028 for the manufacture of planes that don’t comply with the standards. The standard must still be adopted by the agency’s 36-nation governing council, but substantive changes aren’t expected.

The standards would require an average 4 percent reduction in fuel consumption during the cruise phase of flight starting in 2028 when compared with planes delivered in 2015. However, planes burn the most fuel during takeoffs and landings, while cruising at high altitudes is already the most fuel-efficient period.

The agreement is the first of two important opportunities this year to reduce carbon emissions from aviation. The second opportunity will come later this year when ICAO tries to reach an agreement on a “market-based approach” that would use economic incentives to further reduce aviation carbon emissions.

Aviation accounts for about 5 percent of global greenhouse emissions, according to environmentalists. ICAO says it’s actually less than 2 percent.