The International Civil Aviation Organization’s (ICAO) 39th Assembly in Montreal witnessed the signing of a landmark agreement to control CO2 emissions from international aviation.

With 191 countries agreeing to a global market-based measure (GMBM) to “control” CO2 emissions from flying, the deal was reached on Thursday.

A raft of “mitigation measures” the air transport industry was already looking at to cut CO2 emissions would be complemented by the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) of the ICAO, the agency said.

Reuters reported that for countries with big aviation industries, the new system will be voluntary between 2021 and 2026 and then compulsory from 2027. Reuters added that in order to offset any increase in emissions, carbon credits from environmental projects will need to be bought.

“We now have practical agreement and consensus on this issue backed by a large number of states who will voluntarily participate in the GMBM – and from its outset,” Olumuyiwa Benard Aliu, ICAO council president, said in a news release.

“This will permit the CORSIA to serve as a positive and sustainable contributor to global greenhouse gas emissions reduction,” Aliu added.

The Paris Agreement – reached at last year’s COP21 summit – did not cover aviation and hence the ICAO’s announcement is significant. The International Air Transport Association (IATA) praised Thursday’s agreement.

“The historic significance of this agreement cannot be overestimated,” Alexandre de Juniac, director general and CEO of the IATA, said.

“CORSIA is the first global scheme covering an entire industrial sector. The CORSIA agreement has turned years of preparation into an effective solution for airlines to manage their carbon footprint,” Alexandre de Juniac added.

The scheme was described as an “unprecedented deal, the first of its kind for any sector” by the U.K.’s aviation minister, Lord Ahmed.

“For years, the U.K. has pushed to tackle aviation emissions globally,” Ahmed went on to say.

“Now, 191 countries have agreed on a global measure and sent a clear message that aviation will play its part in combating climate change,” Ahmed added.

“It has taken a great deal of effort and understanding to reach this stage, and I want to applaud the spirit of consensus and compromise demonstrated by our Member States, industry and civil society,” remarked ICAO Council President Dr. Olumuyiwa Benard Aliu.

“This will permit the CORSIA to serve as a positive and sustainable contributor to global greenhouse gas emissions reduction,” Aliu added.

Implementation of the CORSIA will include a first phase, from 2024 through 2026 following a pilot phase from 2021 through 2023. For States with very low levels of international aviation activity, Landlocked Developing Countries (LLDCs), Least Developed Countries (LDCs) and Small Island Developing States (SIDS), some exemptions were accepted.

“I would like to thank all those who have been part of this process”, said Dr. Fang Liu, Secretary General of ICAO. “This Resolution is the reflection of the spirit of cooperation and tremendous efforts. The ICAO GMBM endorsed today is an important addition to the basket of measures aviation is pursuing to address CO₂ emissions.”

(Adapted from CNBC & ICAO)