Final answer:
The Montreal Convention deals with international air travel and has not been adopted by all nations, thus not fully replacing the Warsaw Convention. Other treaties like the Geneva Conventions and Paris Climate Accord have different focuses and also require state compliance.
Step-by-step explanation:
The Montreal Convention, which targets issues related to international carriage by air, may not have been adopted by all nations and thus has not entirely replaced the older Warsaw Convention for every UN member state. The statement that "all nations of the world have now adopted the Montreal convention" is inaccurate as adoptions of international treaties can vary among countries. Additionally, there are other conventions, such as those addressing humanitarian law and various international issues, that play a critical role alongside the Montreal Convention. For instance, the Geneva Conventions cover international humanitarian law, and the World Trade Organization (WTO) functions to promote trade while protecting the economies of member nations. The Paris Climate Accord and treaties like the Convention to Eliminate All Forms of Discrimination Against Women (CEDAW) also require states to modify domestic policies in line with international commitments. The Montreal Protocol of 1987 is another significant international agreement that pertains to environmental issues, specifically the phase-out of substances that deplete the ozone layer, and is separate from the Montreal Convention which governs air travel.