About

About this Report

Climate change threatens human health and well-being in the United States. The U.S. Global Change Research Program ( USGCRP) Climate and Health Assessment has been developed to enhance understanding and inform decisions about this growing threat. This scientific assessment, called for under the President’s Climate Action Plan,¹ is a major report of the sustained National Climate Assessment ( NCA) process. The report responds to the 1990 Congressional mandate² to assist the Nation in understanding, assessing, predicting, and responding to human-induced and natural processes of global change. The agencies of the USGCRP identified human health impacts as a high-priority topic for scientific assessment.

The purpose of this assessment is to provide a comprehensive, evidence-based, and, where possible, quantitative estimation of observed and projected climate change related health impacts in the United States. The USGCRP Climate and Health Assessment has been developed to inform public health officials, urban and disaster response planners, decision makers, and other stakeholders within and outside of government who are interested in better understanding the risks climate change presents to human health.

The authors of this assessment have compiled and assessed current research on human health impacts of climate change and summarized the current state of the science for a number of key topics. This assessment provides a comprehensive update to the most recent detailed technical assessment for the health impacts of climate change, the 2008 Synthesis and Assessment Product 4.6 (SAP 4.6), Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems. ³ It also updates and builds upon the health chapter of the 2014 NCA.⁴ While Chapter 1: Introduction: Climate Change and Human Health includes a brief overview of observed and projected climate change impacts in the United States, a detailed assessment of climate science is outside the scope of this report. This report relies on the 2014 NCA⁵ and other peer-reviewed scientific assessments of climate change and climate scenarios as the basis for describing health impacts.

Each chapter of this assessment summarizes scientific literature on specific health outcomes or climate change related exposures that are important to health. The chapters emphasize research published between 2007 and 2015 that quantifies either observed or future health impacts associated with climate change, identifies risk factors for health impacts, and recognizes populations that are at greater risk. In addition, four chapters (Temperature-Related Death and Illness, Air Quality Impacts, Vector-Borne Disease, and Water-Related Illness) highlight recent modeling analyses that project national-scale impacts in these areas.

The geographic focus of this assessment is the United States. Studies at the regional level within the United States, analyses or observations in other countries where the findings have implications for potential U.S. impacts, and studies of global linkages and implications are also considered where relevant. For example, global studies are considered for certain topics where there is a lack of consistent, long-term historical monitoring in the United States. In some instances it is more appropriate to consider regional studies, such as where risk and impacts vary across the Nation.

While climate change is observed and measured on long-term time scales (30 years or more), decision frameworks for public health officials and regional planners are often based on much shorter time scales, determined by epidemiological, political, or budgeting factors. This assessment focuses on observed and current impacts as well as impacts projected in 2030, 2050, and 2100.

The focus of this assessment is on the health impacts of climate change. The assessment provides timely and relevant information, but makes no policy recommendations. It is beyond the scope of this report to assess the peer-reviewed literature on climate change mitigation, adaptation, or economic valuation or on health co-benefits that may be associated with climate mitigation, adaptation, and resilience strategies. The report does assess scientific literature describing the role of adaptive capacity in creating, moderating, or exacerbating vulnerability to health impacts where appropriate. The report also cites analyses that include modeling parameters that make certain assumptions about emissions pathways or adaptive capacity in order to project climate impacts on human health. This scientific assessment of impacts helps build the integrated knowledge base needed to understand, predict, and respond to these changes, and it may help inform mitigation or adaptation decisions and other strategies in the public health arena.

Climate and health impacts do not occur in isolation, and an individual or community could face multiple threats at the same time, at different stages in one’s life, or accumulating over the course of one’s life. Though important to consider as part of a comprehensive assessment of changes in risks, many types of cumulative, compounding, or secondary impacts are beyond the scope of this report. Though this assessment does not focus on health research needs or gaps, brief insights gained on research needs while conducting this assessment can be found at the end of each chapter to help inform research decisions.

The first chapter of this assessment provides background information on observations and projections of climate change in the United States and the ways in which climate change, acting in combination with other factors and stressors, influences human health. It also provides an overview of the approaches and methods used in the quantitative projections of health impacts of climate change conducted for this assessment. The next seven chapters focus on specific climate-related health impacts and exposures: Temperature-Related Death and Illness; Air Quality Impacts; Extreme Events; Vector-Borne Diseases; Water-Related Illness; Food Safety, Nutrition, and Distribution; and Mental Health and Well-Being. A final chapter on Populations of Concern identifies factors that create or exacerbate the vulnerability of certain population groups to health impacts from climate change. That chapter also integrates information from the topical health impact chapters to identify specific groups of people in the United States who may face greater health risks associated with climate change.

The Sustained National Climate Assessment

The Climate and Health Assessment has been developed as part of the U.S. Global Change Research Program’s (USGCRP’s) sustained National Climate Assessment (NCA) process. This process facilitates continuous and transparent participation of scientists and stakeholders across regions and sectors, enabling new information and insights to be synthesized as they emerge. The Climate and Health Assessment provides a more comprehensive assessment of the impacts of climate change on human health, a topic identified as a priority for assessment by USGCRP and its Interagency Crosscutting Group on Climate Change and Human Health ( CCHHG) and featured in the President’s Climate Action Plan.¹

Report Sources

The assessment draws from a large body of scientific, peer-reviewed research and other publicly available resources. Author teams carefully reviewed these sources to ensure a reliable assessment of the state of scientific understanding. Each source of information was determined to meet the four parts of the Information Quality Act ( IQA): utility, transparency and traceability, objectivity, and integrity and security (see Appendix 2: Process for Literature Review). More information on the process each chapter author team used to review, assess, and determine whether a literature source should be cited can be found in the Supporting Evidence section of each chapter. Report authors made use of the findings of the 2014 NCA, peer-reviewed literature and scientific assessments, and government statistics (such as population census reports). Authors also updated the literature search⁶ conducted by the National Institute of Environmental Health Sciences ( NIEHS) as technical input to the Human Health chapter of the 2014 NCA.

Overarching Perspectives

Five overarching perspectives, derived from decades of observations, analysis, and experience, have helped to shape this report: 1) climate change is happening in the context of other ongoing changes across the United States and around the globe; 2) there are complex linkages and important non-climate stressors that affect individual and community health; 3) many of the health threats described in this report do not occur in isolation but may be cumulative, compounding, or secondary; 4) climate change impacts can either be amplified or reduced by individual, community, and societal decisions; and 5) climate change related impacts, vulnerabilities, and opportunities in the United States are linked to impacts and changes outside the United States, and vice versa. These overarching perspectives are briefly discussed below.

Global Change Context

This assessment follows the model of the 2014 NCA, which recognized that climate change is one of a number of global changes affecting society, the environment, the economy, and public health.⁵ While changes in demographics, socioeconomic factors, and trends in health status are discussed in Chapter 1: Introduction: Climate Change and Human Health, discussion of other global changes, such as land-use change, air and water pollution, and rising consumption of resources by a growing and wealthier global population, are limited in this assessment.

Complex Linkages and the Role of Non-Climate Stressors

Many factors may exacerbate or moderate the impact of climate change on human health. For example, a population’s vulnerability 1) may be affected by direct climate changes or by non-climate factors (such as changes in population, economic development, education, infrastructure, behavior, technology, and ecosystems); 2) may differ across regions and in urban, rural, coastal, and other communities; and 3) may be influenced by individual vulnerability factors such as age, socioeconomic status, and existing physical and/or mental illness or disability. These considerations are summarized in Chapter 1: Introduction: Climate Change and Human Health and Chapter 9: Populations of Concern. There are limited studies that quantify how climate impacts interact with the factors listed above or how these interactions can lead to many other compounding, secondary, or indirect health effects. However, where possible, this assessment identifies key environmental, institutional, social, and behavioral influences on health impacts.

Cumulative, Compounding, or Secondary Impacts

Climate and health impacts do not occur in isolation and an individual or community could face multiple threats at the same time, at different stages in one’s life, or accumulating over the course of one’s life. Some of these impacts, such as the combination of high ozone levels on hot days (see Ch. 3: Air Quality Impacts) or cascading effects during extreme events (see Ch. 4: Extreme Events), have clear links to one another. In other cases, people may be threatened simultaneously by seemingly unconnected risks, such as increased exposure to Lyme disease and extreme heat. These impacts can also be compounded by secondary or tertiary impacts, such as climate change impacts on access to or disruption of healthcare services, damages to infrastructure, or effects on the economy.

Societal Choices and Adaptive Behavior

Environmental, cultural, and socioeconomic systems are tightly coupled, and as a result, climate change impacts can either be amplified or reduced by cultural and socioeconomic decisions.⁵ Adaptive capacity ranges from an individual’s ability to acclimatize to different meteorological conditions to a community’s ability to prepare for and recover from damage, injuries, and lives lost due to extreme weather events. Awareness and communication of health threats to the public health community, practitioners, and the public is an important factor in the incidence, diagnosis, and treatment of climate-related health outcomes. Recognition of these interactions, together with recognition of multiple sources of vulnerability, helps identify what information decision makers need as they manage risks.

International Context

Climate change is a global phenomenon; the causes and the impacts involve energy-use, economic, and risk-management decisions across the globe.⁵ Impacts, vulnerabilities, and opportunities in the United States are related in complex and interactive ways with changes outside the United States, and vice versa. The health of Americans is affected by climate changes and health impacts experienced in other parts of the world.