s possible, gradually reduce and prevent air pollution...."17 They also will "develop without undue delay, policies and strategies which shall serve as a means of combating the discharge of air pollutants.''18
They also shall undertake "to develop the best policies and strategies" in order to combat air pollution.19 As a matter of fact, in spite of its appearances, this convention is an operative one and has created a useful framework for everyday cooperation as well as for the development of further international rules that are more stringent.20
A growing number of treaties do not include immediate obligations for the contracting states, instead they develop programmes of action. One of the first was the Paris Convention for the Prevention of Marine Pollution from Land-Based Sources, adopted on 4 June 1974, which provides that, for carrying out the undertakings resulting from that Convention, "the Contracting Parties, jointly or individually as appropriate, shall implement programmes and measures.. "21 It may be considered that such provisions are between "soft" and "hard" treaty obligations, since the content of the duties resulting from the treaty are not defined. As a result, it could hardly be enforced by an international jurisdiction.
Not very different from this method is that of the "pactum contrahendi," i.e. the conclusion of a treaty that mainly provides for cooperation between the contracting parties, hoping that this may result in the adoption of more precise obligations. One of the earliest models in this field was the Convention on the Conservation of Migratory Species of Wild Animals, adopted in Bonn on 23 June 1979, according to which the parties shall endeavour to abide by agreements covering the conservation and management of certain migratory species.22 The most important application of this method, so far, seems to be the 1985 Vienna Convention for the Protection of the Ozone Layer, according to which the parties shall in accordance with the means at their disposal and their capabilities:23 "Co-operate in the formulation of agreed measures, procedures and standards for the implementation of this Convention, with a view to the adoption of protocols and annexes."24
As a matter of fact, the Montreal Protocol of September 1987 had determined the emission levels that different contracting parties should respect and that constitute a directly enforceable legal obligation.25
The Montreal Protocol26 and the two Protocols implementing the 1979 Geneva Convention on Long-Range Transboundary Air Pollution initiated a new method in the development of international regulations that may be called the method of relative standards. According to the Helsinki Protocol of the 1979 Geneva Convention, which provides for the reduction of sulphur emissions: "the Parties shall reduce their national annual sulphur emission or their transboundary fluxes by at least 30 per cent as soon as possible and, at the latest by 1993, using 1980 levels as the basis for calculation of reductions."27
Thus, the obligations accepted by this treaty necessarily vary from one contracting party to the other, since their sulphur emissions in 1980 were not the same. This method seems to be an important innovation in international treaty law.
Difference between the obligations of contracting states may also result from the recognition of the difference between their level of development. The best example of this is Article 5 of the Montreal Protocol on Substances That Deplete the Ozone Layer.28 This provision sets different standards for developing countries than those for industrialized states, but this principle has already been proclaimed in the 1972 Stockholm Declaration.29
The use of umbrella conventions is very frequent in all the new fields where global change has modified international legislative techniques: for example, the international protection of human rights,30 the legal regime of outer space,31 the new Law of the Sea,32 and, of course, environmental protections.33 This means that, a first agreement had to be reached on the principle