Although the general theory of greenhouse warming has been understood by scientists since the end of the nineteenth century, an international regime to address the problem of climate change began to develop only in the late 1980s.11Political scientists use the term "international regime" to refer to a network of rules, institutions, programs, and decision-making procedures governing a given area of international relations (Bodansky, 1995; Krasner, 1983). In the decade and a half since then, the regime has undergone a remarkable evolution. In 1992, states adopted the UN Framework Convention on Climate Change (UNFCCC), which took effect in 1994 and serves as the "constitution" for the international climate change regime.22As of February 17, 2003, 188 states and the European Community had become party to the UNFCCC, making it one of the most widely ratified treaties of any kind. In 1997, the UNFCCC was supplemented by the Kyoto Protocol, which requires industrialized countries to reduce their emissions of carbon dioxide and five other gases that contribute to the greenhouse effect (so-called "greenhouse gases" or GHGs for short). And the 2001 Marrakesh Accords further elaborate the Kyoto Protocol's regulatory regime, setting forth detailed rules for how the Kyoto Protocol will operate. Several general features of the emerging climate change regime are noteworthy. First, the regime has aimed, thus far, at the widest participation possible, due to the global nature of the greenhouse effect and the recognition that human-induced ("anthropogenic") climate change is the "common concern of humankind."33UNFCCC preamble, paragraph 1. This aim has been severely undermined by the withdrawal of the United States from the Kyoto Protocol in 2001, and the reluctance of developing countries to accept quantified limitations on their GHG emissions. Currently, the United States contributes more than one-fifth of global CO2 emissions and all OECD (Organization for Economic Co-operation and Development) countries roughly one half.44World Resources Institute (2003). Moreover, although emissions from developing countries are comparatively low at present, particularly in per capita terms, they are growing rapidly and are projected to surpass industrialized country emissions in the next 20-30 years. Although some have argued that a regime comprising only the dozen largest industrialized and developing countries (which together account for more than three-fourths of global GHG emissions) could potentially be effective, such a regime would be difficult to negotiate, given fears that it would provide a competitive advantage to non-participants and would lack the international legitimacy of a regime representing a true global consensus. Second, the climate change regime exemplifies the "framework convention/protocol" approach to international environmental law - an approach used successfully to address such problems as acid rain in Europe and depletion of the stratospheric ozone layer. As its title indicates, the UNFCCC established the basic framework for the climate change regime.55See generally Barratt-Brown, Hajost, and Sterne (1993), Bodansky (1993), Goldberg (1993), Grubb (1992), and Sands (1992). The 1997 Kyoto Protocol then built on that framework by setting forth specific obligations and mechanisms to control the GHG emissions of industrialized countries.66See generally Breidenich, Magraw, Rowle, and Rubin (1998), Davies (1998), and Oberthur and Ott (1999). Third, the climate change regime has an exceptionally broad scope, encompassing not simply environmental protection as traditionally conceived (that is, limiting emissions of pollutants), but economic and development policies more generally. Virtually the entire range of human activities contribute to GHG emissions. GHG emission scenarios, for example, are highly sensitive to population growth assumptions. (According to one scenario, population growth will account for half of the increase in global CO2 emissions from fossil fuels over the next 60 years.77DeCanio (1992).) Thus, population policy could conceivably play a prominent role in the climate change regime. Fourth, the climate change regime is largely neutral regarding policy options. Although climate change is primarily a problem of carbon dioxide (which accounts for about 70% of the enhanced greenhouse effect to date),88Houghton (1997). fossil fuels (which account for 65-90% of CO2 emissions and 30% of methane emissions),99The reports submitted by industrialized countries under the UNFCCC indicate that fossil fuels account for 97% of their CO2 emissions and CO2 for 75% of their overall GHG emissions. and ultimately coal (which represents more than 90% of the carbon in estimated fossil fuel reservoirs), neither the UNFCCC nor the Kyoto Protocol singles out any particular greenhouse gas or economic sector for special attention. Indeed, while attention has tended to focus thus far on mitigation - an emphasis reflected in the Kyoto Protocol - the UNFCCC addresses adaptation as well. As a result, states have significant flexibility in designing strategies to respond to climate change. This chapter provides an introduction to the international climate change regime. The first section reviews the development of the regime, from the emergence of the climate change issue in the 1980s through the adoption of the 1997 Kyoto Protocol and the 2001 Marrakesh Accords. The subsequent section then outlines the principal elements of the regime, including:•the objective and guiding principles set forth in the UNFCCC;•the regime's governing institutions such as the Conference of the Parties (COP) and financial mechanism;•the emissions limitation commitments set forth in the Kyoto Protocol, and•innovative mechanisms such as emissions trading and the Clean Development Mechanism (CDM).