As the question says international norms, the answer woud relate to measures taken in international levels for the regulation of carbon dioxide. One of the main reasons can be controlling of flying of millitary heliopters and aeroplanes, and indirectly reduction of wars. some common reasons can be like controlling pollution, i.e. reducing the usage of vehicles running by fuels, assuring complete combustion of the fuel, using public transport(if possible) or making use of bicycles, etc. Better answers can include measures taken by international agencies like UNCTAD(United nations Conference on Trade and Development), etc. for the regulation of CO2. This was the best i could answer b'cause i myself was searching for this one.!!
