This article discusses the role that unilateral state action theoretically ought to have ' and practically is likely to have ' in an emerging regime of international environmental regulation. The tendency has been to see solutions to environmental problems in terms of broad environmental treaties and cooperative international approaches, arrangements and institutions. The article argues, however, that any perspective that ignores the role of unilateral state action is likely to prove incomplete and unrealistic since: (1) unilateral state action in the environmental field is a fact of international life; (2) certain types of environmental problems inherently require unilateral state action for their effective solution; and (3) in view of the decentralized character of the international political system, individual states are likely to retain considerable authority to act unilaterally to prevent environmental harm. The most significant problems of environmental regulation may thus involve the allocation among states of jurisdiction to take unilateral action rather than the restriction of state prerogatives in favor of international authority. The article, first suggests a classification of unilateral state environmental actions based on criteria such as the motive for the unilateral action, its principal locus of application, its permanence, the nature of the harm against which it is directed, its impact on foreign interests and its apparent consistency with international law. It then discusses the following questions: (1) What types of unilateral action are states presently taking or likely to take in order to deal with threats or transnational environmental injury? (2) To what extent does unilateral action raise problems under existing international law? (3) What are the potential advantages and disadvantages of unilateral action in terms of its possible effects on transnational environmental problems, international relations and trade, and on the future development of international environmental law? (4) Is it possible to accommodate the pressures that lead to unilateral action within a multilateral framework which can avoid or mitigate the problems unilateral action creates? (5) Is it possible to make any broad judgment as to the appropriate roles of both unilateral and multilateral action in an effective scheme of international environmental regulations? It concludes by suggesting that: (1) unilateral state action to prevent international environmental injury is likely to play an important and continuing role in efforts to deal with international environmental problems; (2) the desirability and effectiveness of such unilateral action will depend on a numbers of factors, including the alternatives practically available; and (3) a comprehensive and effective system of international environmental control will require an imaginative and realistic mix of both unilateral state approaches and international oversight, standards, procedures and regulatory authority.
