The European Commission has endorsed last week's deal at the ICAO to tackle growth in international aviation's carbon emissions.
Under the agreement, airlines emitting more than 10,000 tons of CO2 per year will be required to offset any emissions above 2020 levels by buying credits from other sectors.
European Union member states are among the 65 countries that will participate in the scheme from its pilot phase in 2021, while others will have to join from its mandatory phase in 2027.
Offsetting is a different solution to the EU's Emission Trading Scheme under which a fixed allocation of emissions credits are bought and traded because it places no upper limit on emissions growth. Instead, any increase in aviation's global warming impact should be canceled out by a reduction in another sector.
European Commissioner for Transport Violeta Bulc says that 80 per cent of airlines' extra CO2 from 2021 to 2035 will be offset as a result, which sounds promising.
Moreover, offsetting is in many respects the ideal solution for aviation – an industry with no realistic technological fix for ever-growing overall emissions. It makes sense, therefore, for it to trade with industries that do have alternatives, such as power generation.
However, offsetting schemes are only as effective as the permits they trade in, and it's usually impossible to prove that a credit to emit one ton of CO2 equals a net one-ton reduction elsewhere.
For instance, a new solar power station in Germany might justify several thousand offsetting credits for the aviation industry. However, quirks of that country's energy policy have allowed its coal sector to prosper, and greenhouse gas emission in Germany actually rose last year, despite almost a third of its power coming from renewables.
Another problem is that one ton of CO2 emitted at high altitude is more damaging than a ton at ground level.
The ICAO has provided little detail about what type of offsets will be acceptable, but the EU hopes that a triennial review process will ensure that standards are maintained.
"It is not 'Mission Accomplished'," says Bulc. "Over the next two years, ICAO will lay out the technical rules of the Global Market-Based Measure, and we will remain vigilant that it lives up to our expectations and is well implemented."