Abstract The rapid growth of air traffic and the expectation that this growth will continue into the foreseeable future co-exist with the growing awareness of the need to limit or reduce the impact of human activities upon the world's climate and the natural environment. To successfully realise these twin goals, it is necessary for all parties involved - aircraft makers and users, atmospheric scientists, regulators, etc - to cooperate to achieve a comprehensive understanding of the issues and options. AERONET is a project which demonstrates the feasibility and utility of such cooperation.