dynamics, and of human behaviors, policy preferences, and choices; and on assumptions about the future availability of technologies for reducing emissions (including cobenefits and unintended consequences of mitigation). Yet the underlying human dimensions research needed to understand and develop sound adaptation strategies is a major gap in the CCSP. Although adaptation, mitigation, and vulnerability research would be needed for all the societal issues in the proposed new research framework, an additional focused research effort would help speed results. A critical step in the process is for agencies with appropriate expertise to increase funding and take a leadership role in supporting, managing, and directing this research.

Initiate a national assessment process with broad stakeholder participation to determine the risks and costs of climate change impacts on the United States and to evaluate options for responding.

A comprehensive national assessment with periodic reporting provides a mechanism to build communication with stakeholder groups and to identify evolving science and societal needs and priorities. A useful assessment does not merely summarize published studies, but has the ability to undertake targeted research to produce new insights, observations, models, and decision support services. Results of the assessment could be used to help determine priorities for federal research on impacts, mitigation, and adaptation; provide a focus for integrated science-policy assessments and enhanced regional modeling and predictions; and build human and institutional capacity to support decision making. Although the CCSP is mandated to carry out a national assessment every 4 years, the last one to involve a broad range of stakeholders was conducted a decade ago. From 2006 to 2008, the CCSP published 21 synthesis and assessment reports on a range of topics and an overarching synthesis. Although useful, the collection does not add up to a comprehensive national assessment. A new assessment will require strong political and scientific leadership, adequate resources, a careful planning process, and engagement of stakeholders at all stages of the process.