Global warming' and 'climate change,' allegedly aggravated as well as caused by the emission of so-called greenhouse gases and greenhouse effect, are becoming critical issues to be settled for the survival of all human beings and conservation of ecological system. Upon realizing the seriousness of global warming and climate change, international society established the so-called 'international climate change regime' based on the two major relevant conventions, 「United Nations Framework Convention on Climate Change」(UNFCCC) and 「Kyoto Protocol to the United Nations Framework Convention on Climate Change」(Kyoto Protocol). These two international treaties respectively provide legal measures regarding states' obligation to reduce the emission of greenhouse gases and prevent global warming and climate change.
However, in several respects, such as lack of effective implementation system, consensus of future duty to reduce the emission of greenhouse gases, practical means to claim state responsibility and so on, this treaty regime is still incomplete as a legal basis of states' duty to prevent climate change. Accordingly, some questions have been raised, such as whether any other rule of international law applicable to the states' duty to prevent climate change exists outside of the treaty regime and whether the existence of the treaty regime automatically excludes the application of relevant general international rule. The 'No-harm rule' under customary international law is located in the center of these discussions. If this rule, along with the treaty regime, is applicable and effective as a direct legal basis for the states' duty to prevent climate change, the defects of existing treaty regime will be significantly cured, as well as the legal framework of states' prevention duty of and responsibility for climate change will be strengthened.
Based on this recognition, this paper, starting with the general overview of the existing climate change regime, not only reviewed the concept and legal status of the 'No-harm rule' as an established principle under customary international law but also studied the applicability of the 'No-harm rule' to the states' prevention duty of and responsibility for climate change through the analysis of relationship between the existing treaty regime and the 'No-harm rule. Through this discussion, the author expects this paper can contribute to make the legal system concerning the states' duty to prevent climate change stronger and more effective.