The International Civil Aviation Organization (ICAO) has developed a global carbon offsetting system for the aviation industry, which is the first of its kind. This system is expected to help slow down the growth of emissions from commercial flights and will cost the industry less than 2 percent of its revenues. However, individual governments still need to take action to implement the agreement's limitations. The system will start as voluntary from 2021 to 2026 and become mandatory from 2027 for countries with larger aviation industries. Airlines will need to purchase carbon credits from specific environmental projects worldwide to offset the increase in emissions. According to Olumuyiwa Benard Aliu, president of ICAO's governing council, the system is a result of compromises and consensus among stakeholders. Aliu stated that objections from a few countries would not stop the plan from moving forward. He mentioned that 65 countries, which account for over 80 percent of aviation activity, have already joined the voluntary first phases, exceeding the agency's expectations. Participation is expected to increase further. The main tensions are between developed nations, who have been the biggest emitters of greenhouse gases in the past, and emerging and developing countries worried about the additional costs affecting growth. Russia and India have declined to participate in the voluntary phases, claiming that the deal unfairly burdens emerging countries. On the other hand, China has announced its intention to join the voluntary phase. Brazil, which previously had concerns, has now expressed support for the deal without confirming whether it will participate in the initial phases. According to ICAO data, the agreement is estimated to cost airlines between $1.5 billion and $6.2 billion in 2025, depending on future carbon prices, and no more than 1.8 percent of industry revenues by 2035. Despite airlines operating on slim margins, averaging 4 percent over the past decade, the International Air Transport Association has stated that the deal is more cost-effective than a fragmented system of national and regional climate agreements. IATA Vice President Paul Steele believes the additional cost is manageable for the industry. The US Department of State, which advocated for a deal, stated that it would lead the industry towards sustainable, carbon-neutral growth. However, environmentalists argued that due to the voluntary phase and exceptions for smaller markets, the scheme would not achieve its goals. The International Council on Clean Transportation estimated that airlines would only need to offset about three-quarters of growth after 2021, or one-quarter of total international traffic. Critics also expressed concerns about the deal's reliance on offsets, with Transport and Environment director Bill Hemmings stating that it would not reduce the demand for jet fuel. Discussions will now focus on the technical aspects of the agreement, particularly regarding the types of offset credits that will be deemed acceptable. The deal was approved by an assembly of ICAO's 191 member states in Montreal and will apply to international passenger and cargo flights, as well as business jets that emit more than 10,000 tonnes of emissions annually. Previous negotiations nearly led to a trade war before the 2013 ICAO assembly, when the European Union, frustrated by slow progress, required foreign airlines to purchase credits under its program. This move was seen as a violation of sovereignty by China and other countries. The agreement was reached just one day after the Paris climate change accord went into effect. Aviation was not included in the agreement, even though the sector is responsible for approximately 2 percent of carbon dioxide emissions, a greater amount than some industrialized countries. With the industry anticipating a doubling of passenger numbers to 7 billion by 2034, it is crucial to limit the increase in aircraft pollution in order to meet the temperature goals set by the Paris agreement, according to Lou Leonard, a vice president at the World Wildlife Fund.