UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
The Earth’s changing climate is affecting human health and the environment in many ways. Across the United States (U.S.), temperatures are rising, snow and rainfall patterns are shifting, and extreme climate events are becoming more common. Scientists are confident that many of the observed changes in the climate are caused by the increase in greenhouse gases (GHGs) in the atmosphere. As GHG emissions from human activities increase, many climate change impacts are expected to increase in both magnitude and frequency over the coming decades, with risks to human health, the economy, and the environment.
Actions can be taken now to reduce GHG emissions and avoid many of the adverse impacts of climate change. Quantifying the benefits of reducing GHG emissions (i.e., how GHG mitigation reduces or avoids impacts) requires comparing projections of climate change impacts and damages in a future with policy actions and a future without policy actions. Looking across a large number of sectors, this report communicates estimates of these benefits to the U.S. associated with global action on climate change.
About this Report
This report summarizes and communicates the results of EPA’s ongoing Climate Change Impacts and Risk Analysis (CIRA) project. The goal of this work is to estimate to what degree climate change impacts and damages to multiple U.S. sectors (e.g., human health, infrastructure, and water resources) may be avoided or reduced in a future with significant global action to reduce GHG emissions, compared to a future in which current emissions continue to grow. Importantly, only a small portion of the impacts of climate change are estimated, and therefore this report captures just some of the total benefits of reducing GHGs.
To achieve this, a multi-model framework was developed to estimate the impacts and damages to the human health and welfare of people in the U.S. The CIRA framework uses consistent inputs (e.g., socioeconomic and climate scenarios) to enable consistent comparison of sectoral impacts across time and space. In addition, the role of adaptation is modeled for some of the sectors to explore the potential for risk reduction and, where applicable, to quantify the costs associated with adaptive actions.
The methods and results of the CIRA project have been peer reviewed in the scientific literature, including a special issue of Climatic Change entitled, “A Multi-Model Framework to Achieve Consistent Evaluation of Climate Change Impacts in the United States.” The research papers underlying the modeling and results presented herein are cited throughout this report and are listed in Section B of the Technical Appendix.
Interpreting the Results
This report presents results from a large set of sectoral impact models that quantify and monetize climate change impacts in the U.S., with a primary focus on the contiguous U.S., in futures with and without global GHG mitigation. The CIRA analyses are intended to provide insights about the potential direction and magnitude of climate change impacts and the benefits (avoided impacts) to the U.S. of global emissions reductions. However, none of the estimates presented in this report should be interpreted as definitive predictions of future impacts at a particular place or time.
The CIRA analyses do not evaluate or assume specific GHG mitigation or adaptation policies in the U.S. or in other world regions. Instead, they consider plausible scenarios to illustrate potential benefits of significant GHG emission reductions compared to a business-as-usual future. The results should not be interpreted as supporting any particular domestic or global mitigation policy or target. A wide range of global mitigation scenarios could be modeled in the CIRA framework,2 and results would vary accordingly. For ease of communicating results, however, this report focuses on a future where the increase in average global temperature is limited to approximately 2°C (3.6°F) above preindustrial levels—a goal relevant to international discussions on GHG emission reductions.
This report includes as many climate change impacts as feasible at present, but is not all-inclusive. It is not intended to be as comprehensive as major assessments, such as those conducted by the U.S. Global Change Research Program (USGCRP), which capture a wider range of impacts from the published literature.4 By using a consistent set of socioeconomic and climate scenarios, CIRA produces apples-to-apples comparisons of impacts across sectors and regions—something that is not always achieved, or even sought, in the major assessments. Also, the assessments typically do not monetize damages, nor do they focus on quantifying mitigation benefits. CIRA’s ability to estimate how global GHG mitigation may benefit the U.S. by reducing or avoiding climate change impacts helps to fill an important literature and knowledge gap.
The CIRA analyses do not serve the same analytical purpose nor use the same methodology as the Social Cost of Carbon (SCC), an economic metric quantifying the marginal global benefit of reducing one ton of carbon dioxide (CO2).5 In addition, the costs of reducing GHG emissions,6 and the health benefits associated with co-reductions in other air pollutants, are well-examined elsewhere in the literature7 and are beyond the scope of this report.
About the United States Environmental Protection Agency
Born in the wake of elevated concern about environmental pollution, EPA was established on December 2, 1970 to consolidate in one agency a variety of federal research, monitoring, standard-setting and enforcement activities to ensure environmental protection. Since its inception, EPA has been working for a cleaner, healthier environment for the American people.