After much discussion, the United Nations' aviation agency plans to set limits on emissions from international airline flights.
The agreement ratified by members of the UN International Civil Aviation Organization (ICAO) sets airlines' carbon emissions in the year 2020 as the ceiling of the total amount that will be legally allowed.
Airlines that exceed those limits in subsequent years will have to offset them through the purchase of credits, or by investing in projects that limit greenhouse-gas emissions.
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The plan marks a major step to address carbon emissions from aviation, which have received much less attention from regulators than emissions from road vehicles.
But it may take time for the full benefit to be felt.
Most airlines are expected to exceed the emissions cap, at least initially, notes The New York Times (subscription required).
Southwest Airlines Boeing 737 (Image: Flickr user Aero Icarus, used under CC license)
The agreement's success also relies on countries independently working to implement it.
The first phase of the agreement—covering 2021 to 2027—is voluntary, but countries will be required to participate in the second phase, which covers 2028 to 2035.
Full compliance for both phases could eliminate 2.5 billion tons of carbon emissions, according to the Environmental Defense Fund.
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So far, 65 countries have indicated they will participate in the initial, voluntary phase.
That includes the U.S., China, and the 44 nations that make up the European Union's aviation conference.
Russia has no current plans to participate in the voluntary phase, and India has expressed "reservations" over certain aspects of the agreement, according to The New York Times.
Boeing 787 Dreamliner
The agreement does have the backing of the airline industry, which may be expecting the added cost of compliance to be offset by fuel savings.
It only applies to international flights, which account for around 60 percent of aviation.
Emissions from domestic flights fall under the Paris climate-change accord signed by U.N. members last year.
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International flights were left out of that agreement because airlines complained that they would have been forced to deal with regulations country by country.
The global nature of the airline industry has made setting emissions limits challenging.
Aviation currently accounts for around 2 percent of global carbon emissions, but but many analysts believe that share could triple by the middle of the century if projected growth in air travel occurs.