Implementing global aviation emissions plan no simple task

[WASHINGTON] Concessions made by the United Nations' aviation body to wrap up two weeks of tense negotiations could make achieving the goal of a market-based measure to cap carbon emissions from airlines harder to achieve.

The International Civil Aviation Organization (ICAO) agreed in Montreal on Friday to design a global scheme to reduce the growth of the sector's greenhouse gas emissions. The scheme will be hashed out in 2016 and is intended to start in 2020.

But existing differences between countries sharpened at…