If policymakers and the public are to be adequately informed about the climate change threat, climate modeling needs to include components far outside its conventional boundaries. An integration of climate chemistry and meteorology, oceanography, and terrestrial biology has been achieved over the past few decades. More recently the scope of these studies has been expanded to include the human systems that influence the planet, the social and ecological consequences of potential change, and the political processes that lead to attempts at mitigation and adaptation. Fore example, key issues – like the relative seriousness of climate change risk, the choice of long-term goals for policy, and the analysis of today’s decisions when uncertainty may be reduced tomorrow – cannot be correctly understood without joint application of the natural science of the climate system and social and behavioral science aspects of human response. Though integration efforts have made significant contributions to understanding of the climate issue, daunting intellectual and institutional barriers stand in the way of needed progress. Deciding appropriate policies will be a continuing task over the long term, however, so efforts to extend the boundaries of climate modeling and assessment merit long0term attention as well. Components of the effort include development of a variety of approaches to analysis, the maintenance of a clear division between close-in decision support and science/policy research and the development of funding institutions that can sustain integrated research over the long haul. (© 2004 International Union of Geodesy and Geophysics and the American Geophysical Union)