Executive Summary -- Introduction -- Scope and Approach of the SAP 4.6 1-3 -- Climate Change in the United States : Context for an Assessment of Impacts on Human Systems -- Rising temperatures -- Trends in precipitation -- Rising sea levels and erosion of coastal zones -- Changes in Extreme Conditions -- Population Trends and Migration Patterns : A Context for Assessing Climate-related Impacts -- Trends in total U.S. Population -- Migration patterns -- Complex Linkages : The Role of Non-climate Factors -- Economic status -- Technology -- Infrastructure -- Human and Social Capital and Behaviors -- Institutions -- Interacting effects -- Reporting Uncertainty in SAP. Human health -- Introduction -- Observed Climate-Sensitive Health Outcomes in the United States -- Thermal Extremes: Heat Waves -- Thermal Extremes : Cold Waves -- Extreme Events : Hurricanes, Floods, and Wildfires -- Indirect Health Impacts of Climate Change -- Projected Health Impacts of Climate Change in the United States -- Heat-Related Mortality -- Hurricanes, Floods, Wildfires, and Health Impacts -- Vectorborne and Zoonotic Diseases -- Water- and Foodborne Diseases -- Air Quality Morbidity and Mortality -- Vulnerable Regions and Subpopulations -- Vulnerable Regions -- Specific Subpopulations at Risk -- Adaptation -- Actors and Their Roles and Responsibilities for Adaptation -- Adaptation Measures to Manage Climate Change-Related Health Risks -- Conclusions. This report, the Synthesis and Assessment Product 4.6 (SAP 4.6), focuses on impacts of global climate change, especially impacts on three broad dimensions of the human condition: human health, human settlements, and human welfare. The SAP 4.6 has been prepared by a team of experts from academia, government, and the private sector in response to the mandate of the U.S. Climate Change Science Program's Strategic Plan (2003). The assessment examines potential impacts of climate change on human society, opportunities for adaptation, and associated recommendations for addressing data gaps and near- and long-term research goals.