GHGs: what gases, from what sources, when and where, through what specific technology investments or changes in management practices, motivated and coordinated by what policies, with what co-benefits¹ or unintended consequences, and monitored and verified through what means? Other questions focus on the specific impacts that are expected and the actions that can be taken to prepare for and adapt to them, such as reducing vulnerabilities or improving society’s coping and adaptive capacity.

This report explores what these emerging questions and decision needs imply for future scientific learning about climate change and for the scientific research enterprise. As the need for science expands to include both improving understanding and informing and supporting decision making, the production, synthesis, and translation of scientific knowledge into forms that are useful to decision makers becomes increasingly important. It may also imply a need to change scientific practices, with scientists working more closely with decision makers to improve the scientific decision support that researchers can offer. However, even with this decision focus, scientific knowledge cannot by itself specify or determine any choice. It cannot tell decision makers what they should do; their responsibilities, preferences, and values also influence their decisions. Science can inform decisions by describing the potential consequences of different choices, and it can contribute by improving or expanding available options, but it cannot say what actions are required or preferred.

This report describes what has been learned about climate change. It then identifies the most critical current research needs, including research needed to improve our understanding of climate change and its impacts and research related to informing decision makers and allowing them to respond more effectively to the challenges of climate change. As directed by the charge to the panel (see Appendix B), this report covers the broad scientific territory of understanding climate change and its interactions with humans and ecosystems, including responses to climate change. Thus, it spans the breadth of “climate change science,” which in this report is defined to include research in the physical, social, ecological, environmental, health, and engineering sciences, as well as research that integrates these and other disciplines.

The following chapters, which are broken into two parts, discuss the contributions that climate change science has made and can make in advancing our understanding of climate change and in supporting climate-related decisions. The five chapters in Part I