It's because of disagreement over how emissions that cross region borders should be allocated: do they belong towards the nation of departure or country of origin? How are connecting flights accounted for? The tensions in achieving international aviation and delivery deals are discussed in detail from the Carbon Temporary here. https://professionalcleaningservi85959.mdkblog.com/35290728/the-fact-about-emissions-reporting-that-no-one-is-suggesting