Agencies across the federal government, such as the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration, collect and manage many types of climate information, including observational records from satellites and weather monitoring stations on temperature and precipitation; projections from complex climate models; and other tools to make this information more meaningful to decision makers. Such information includes the following: Information and analysis about observed climate conditions. This includes information on, for example, temperature, precipitation, drought, storms, and sea level rise and how they may be changing in the local area. This type of information can be most easily conveyed by graphs and maps with some statistics on trends, variability, and data reliability. Information about observed climate impacts and vulnerabilities. This includes site-specific and relevant baselines of environmental, social, and economic impacts and vulnerabilities, resulting from observed changes in the climate against which past and current decisions can be monitored, evaluated, and modified over time. Projections of what climate change may mean for the local area. This includes, for example, projections based on easily understandable best- and worst-case scenarios with confidence intervals and probability estimates and examples of potential climate impacts. The projections may need to be downscaled from complex global-scale climate models to provide climate information at a geographic scale relevant to decision makers. Then, the information would need to be translated into impacts at the local level, such as how increased streamflow for a particular river may increase flooding. Information on the economic and health impacts of climate change. Observed and projected local impacts must be translated into costs and benefits, as this information is needed for many decision-making processes. Entities within the Executive Office of the President, such as the Council on Environmental Quality and the Office of Science and Technology Policy, have led specific government-wide climate information efforts, such as USGCRP’s May 2014 Third National Climate Assessment, which summarizes the impacts of climate change on the United States, now and in the future. Methods used to estimate the potential economic effects of climate change in the United States are based on developing research from a small but growing number of researchers. These methods are complex because they link different types of complicated climate and economic models to assess how projected changes in the climate could affect different sectors and regions. They produce imprecise results because of information and modeling limitations associated with (1) climate modeling uncertainty; (2) limited information on which to base models for specific economic sectors; (3) incomplete coverage of sectors, interactions among sectors, and climate change impacts; and (4) challenges of modeling over long time frames. Nonetheless, according to several experts we interviewed, the methods can convey useful insight into broad themes about potential climate damages across sectors in the United States. Methods used to estimate the potential economic effects of climate change in the United States are based on developing research being undertaken by a small but growing number of researchers, according to the literature we reviewed and several experts we interviewed. Researchers began developing methods to understand the economics of climate change starting in the early 1990s. These original methods— primarily designed to analyze the economic benefits and costs of reducing greenhouse gas emissions—typically assess the economic effects of climate change at a global or multinational scale, with little detailed information about specific regions or sectors within a country. As a result, some experts said that these original methods produce limited information about the economic effects of climate change within different sectors in the United States. Since the early 2000s, researchers have developed new methods that provide more detailed information about the economic effects of climate change in the United States. Advances in knowledge about the historical relationships between changes in temperature, precipitation, and other climatic variables and the economy; access to data and information about the physical impacts of climate change; and a growth in computing power, among other things, have enabled the development of methods to assess economic effects in specific sectors and regions of the United States, according to literature we reviewed. To date, the new methods have been used primarily to quantify the economic effects of climate change on certain economic sectors, such as agriculture, health, and energy, but the research has been expanding to include additional sectors, such as infrastructure and water resources. Only recently have studies analyzed the economic effects of climate change using frameworks that can compare effects across different sectors and regions within the United States on a national scale. According to many experts we interviewed, the following are the only two such national-scale research studies: American Climate Prospectus: This study was published in October 2014 by the Rhodium Group and assessed the economic effects of potential changes in temperature, precipitation, sea level, and extreme weather events on six sectors of the U.S. economy—coastal property, health, agriculture, energy, labor productivity, and crime— within different regions of the country. According to the study, its intent was to provide information on the probability, timing, and scope of a set of economically important climate change impacts comparable across sectors, rather than a conclusive answer about how much climate change will cost the United States. The study’s authors noted that they designed a research framework that could expand and improve as the climate science and economics fields continue to develop. Climate Change Impacts and Risks Analysis: This is an ongoing research project coordinated by the Environmental Protection Agency (EPA), which published a summary study in 2015. The goal of the study was to assess the extent to which reducing global greenhouse gas emissions may help avoid or reduce climate change impacts and adverse economic effects on six U.S. sectors—health, infrastructure, electricity, water resources, agriculture and forestry, and ecosystems—and enabled the comparison of climate risks across these sectors. According to the authors of the Climate Change Impacts and Risk Analysis study, the study estimated the benefits to the United States of global action on climate change. As such, the analysis presented in the report did not inform on alternative actions and did not constitute a benefit-cost assessment of actions to address climate change. In addition, EPA officials stated that the report was meant to convey broad themes about climate damages across sectors of the United States based on peer-reviewed data and methods. Like the authors of the American Climate Prospectus study, the authors of the Climate Change Impacts and Risk Analysis study noted in the report that the breadth and depth of the project, including the number of sectors covered, will expand in future work as the fields of climate science and economics continue to develop. According to EPA officials, this expanded research will contribute physical and economic information to USGCRP’s next National Climate Assessment. Methods used to estimate the potential economic effects of climate change in the United States are complex because, according to literature we reviewed and many experts we interviewed, they use different types of complicated climate and economic models that are linked together in a sequential framework that uses the results of one model as input to another. The different types of climate and economic models include the following: Climate models: Climate models are mathematical representations of physical, chemical, and biological processes in Earth’s climate system, including the atmosphere, land surface, ocean, and sea ice. These models use scenarios of future greenhouse gas emissions as input, such as a scenario in which current trends in greenhouse gas emissions continue or a scenario in which future emissions are reduced. Based on these scenarios, the models simulate future changes in climate variables, such as changes in temperature and the amount of precipitation. In the United States, global-scale climate models are developed at federally funded institutions, such as the National Center for Atmospheric Research. The American Climate Prospectus and Climate Change Impacts and Risk Analysis studies both used climate models from the National Center for Atmospheric Research, including the Model for the Assessment of Greenhouse- gas Induced Climate Change and the Community Atmosphere Model. Economic models for individual sectors: These models estimate the direct economic effects in certain sectors from changes in climate variables, such as temperature, and related climate impacts, such as sea level rise. Some economic models for individual sectors are based on relatively new econometric research that uses historically observed relationships between climate variables and economic effects to assess the potential economic effects of climate change on certain segments of the economy. For example, the American Climate Prospectus study used analyses of the historical relationships among temperature and changes in mortality, labor productivity, and violent crime, among other things, to project the economic effects of climate change. Other types of sector-specific models use known or theoretical relationships among climate variables and economic effects to make projections. These types of process-based models include, for example, the Forest and Agricultural Sector Optimization Model, used in the Climate Change Impacts and Risks Analysis study, which estimates changes in market outcomes associated with projected impacts of climate change on U.S. crop and forest yields. The 2015 Climate Change Impacts and Risks Analysis report included 18 process-based models and 2 econometric models, according to EPA officials. Also, a version of the U.S. Energy Information Administration’s National Energy Modeling System, maintained by the Rhodium Group and used in the American Climate Prospectus study, models the impact of changes in temperature on energy demand, power generation, and electricity costs. Economy-wide models: These models—called Computable General Equilibrium (CGE) models—can help assess how the entire economy, including individual sectors or regions, might react to the impacts of climate change and how their reactions can have implications for other sectors and regions. For example, as a result of changes in climate (e.g., higher temperatures), increases in energy demand and costs can increase the price of a wide range of goods, and decreases in crop yields in Iowa can affect food prices nationwide. As they encompass multiple sectors in a model of the U.S. economy, CGE models can more fully account for interactions between sectors than individual sector models can, potentially affecting findings on the effects of climate change. The American Climate Prospectus used a CGE model to examine how these types of interactions among sectors affect the magnitude and regional variation of effects on the sectors analyzed in the study.