The first global carbon offsetting system for the aviation industry, created by the International Civil Aviation Organization (ICAO), is expected to help reduce emissions from commercial flights without significantly impacting industry revenues. While individual governments still need to enforce the agreement's limits, the system will be voluntary from 2021 to 2026 and mandatory from 2027 for states 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 the result of compromises and consensus. Aliu stated that objections from a small number of countries would not derail the plan. He mentioned that participation in the voluntary first phases by 65 countries, covering over 80 percent of aviation activity, exceeded the agency's expectations and is expected to continue growing. The tensions revolved around developed nations, which have been responsible for most greenhouse gas emissions in the past, and emerging and developing countries that are concerned added costs could hinder growth. Russia and India have announced they will not participate in the voluntary phases, arguing that the deal unfairly burdens emerging countries. However, China has stated its intention to join the voluntary phase. Brazil, which had previously expressed concerns, has now shown support for the deal. However, it has not confirmed whether it will participate in the initial stages. According to ICAO figures, the agreement is expected to cost airlines between $1.5 billion and $6.2 billion in 2025, depending on future carbon prices. This amounts to no more than 1.8 percent of industry revenues by 2035. Despite airlines' slim profit margins, with an average of 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. Paul Steele, a vice president of IATA, stated that although the deal represents an additional cost for the industry, it is manageable. The US Department of State has advocated for a deal that aims to lead the industry towards sustainable, carbon-neutral growth. However, environmentalists argue that the voluntary phase and exceptions for smaller markets will prevent the scheme from achieving its objectives. The International Council on Clean Transportation predicts that airlines will only need to offset around three-quarters of growth post-2021, which equates to a quarter of total international traffic. Critics also question the deal's heavy reliance on offsets, with Transport and Environment director Bill Hemmings stating that air travel is a major contributor to environmental damage and this agreement will not reduce the demand for jet fuel. Discussions will now focus on the technical specifics of the agreement, particularly the types of offset credits that will be deemed acceptable. The deal, which was approved by an assembly of ICAO's 191 member states in Montreal, will be applicable to international passenger and cargo flights, as well as business jets that produce over 10,000 tonnes of emissions annually. Prior negotiations almost led to a trade dispute before the 2013 ICAO assembly, as the European Union, frustrated by slow progress, mandated foreign airlines to purchase credits under its program. This move was seen as a violation of sovereignty by China and other nations. The agreement was reached shortly after the Paris agreement to combat climate change came into effect. The aviation sector was not included in the agreement, even though it is responsible for around 2% 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 reduce 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.