Reducing greenhouse gas emissions would benefit the health of Americans in the near and long term (high confidence). By the end of this century, thousands of American lives could be saved and hundreds of billions of dollars in health-related economic benefits gained each year under a pathway of lower greenhouse gas emissions (likely, medium confidence).

This finding is from chapter 14 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The chapter evaluated the scientific evidence of the health risks of climate change, focusing primarily on the literature published since the cut off date (approximately fall 2015) of the U.S. Climate and Health Assessment.f1e633d5-070a-4a7d-935b-a2281a0c9cb6 A comprehensive literature search was performed by federal contractors in December 2016 for studies published since January 1, 2014, using PubMed, Scopus, and Web of Science. An Excel file containing 2,477 peer-reviewed studies was provided to the author team for it to consider in this assessment. In addition to the literature review, the authors considered recommended studies submitted in comments by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The focus of the literature was on health risks in the United States, with limited citations from other countries providing insights into risks Americans are or will likely face with climate change. A full description of the search strategy can be found at https://www.niehs.nih.gov/CCHH_Search_Strategy_NCA4_508.pdf. The chapter authors were chosen based on their expertise in the health risks of climate change. Teleconferences were held with interested researchers and practitioners in climate change and health and with authors in other chapters of this Fourth National Climate Assessment (NCA4).

The U.S. Climate and Health Assessmentf1e633d5-070a-4a7d-935b-a2281a0c9cb6 did not consider adaptation or mitigation, including economic costs and benefits, so the literature cited includes research from earlier years where additional information was relevant to this assessment.

For NCA4, Air Quality was added as a report chapter. Therefore, while Key Messages in this Health chapter include consideration of threats to human health from worsened air quality, the assessment of these risks and impacts are covered in Chapter 13: Air Quality. Similarly, co-benefits of reducing greenhouse gas emissions are covered in the Air Quality chapter.

Description of evidence base:

Benefits of mitigation associated with air quality, including co-benefits of reducing greenhouse gas emissions, can be found in Chapter 13: Air Quality. This Key Message is consistent with and inclusive of those findings.

Multiple individual lines of evidence across several health topic areas demonstrate significant benefits of greenhouse gas emission reductions, with health impacts and health-related costs reduced by approximately half under RCP4.5 compared to RCP8.5 by the end of the century, based on comprehensive multisector quantitative analyses of economic impacts projected under consistent scenarios (Ch. 13: Air Quality).4308e866-5976-4181-8102-24b521ff4033^,0b30f1ab-e4c4-4837-aa8b-0e19faccdb94^,0006123e-10a3-4501-a89c-95a7921a9c3d^,00234d41-c8e2-49c1-8b7a-8a2c0ad9b6df^,6e83fde3-5f98-4fd1-ae2c-d11aced414ac^,a5d430bc-5756-42d1-924f-3dbc927e69c4^,f9703346-dc6b-4b3e-aad6-2643c74f5292^,8e30bef3-ce8e-4df4-879b-21f809b02998^,bbca6337-718b-4289-b6e7-0a2f6c1cb8f1^,28077cd1-c29f-48ae-a068-2cdcef880807^,54a66159-1675-43bb-b5d3-a9b7f283e4de^,fad9e8ec-8951-4daa-9a9c-e093ef86af16 The economic benefits of greenhouse gas emissions reductions to the health sector could be on the order of hundreds of billions of dollars annually by the end of the century.

Heat: Greenhouse gas emission reductions under RCP4.5 could substantially reduce the annual number of heat wave days (for example, by 21 in the Northwest and by 43 in the Southeast by the end of the century);a5d430bc-5756-42d1-924f-3dbc927e69c4 the number of high-mortality heat waves;f9703346-dc6b-4b3e-aad6-2643c74f5292^,ea2ea20a-5d62-49ac-a89b-9a7951711a1b and heat wave intensities.a5d430bc-5756-42d1-924f-3dbc927e69c4^,ea2ea20a-5d62-49ac-a89b-9a7951711a1b The EPA (2017)0b30f1ab-e4c4-4837-aa8b-0e19faccdb94 estimated city-specific relationships between daily deaths (from all causes) and extreme temperatures based on historical observations that were combined with the projections of extremely hot and cold days (average of three years centered on 2050 and 2090) using city-specific extreme temperature thresholds to project future deaths from extreme heat and cold under RCP8.5 and RCP4.5 in five global climate models (GCMs). In 49 large U.S. cities, changes in extreme temperatures are projected to result in over 9,000 premature deaths per year under RCP8.5 by the end of the century without adaptation ($140 billion each year); under RCP4.5, more than half these deaths could be avoided annually ($60 billion each year).0b30f1ab-e4c4-4837-aa8b-0e19faccdb94

Labor productivity: Hsiang et al. (2017)fad9e8ec-8951-4daa-9a9c-e093ef86af16 and the EPA (2017)0b30f1ab-e4c4-4837-aa8b-0e19faccdb94 estimated the number of labor hours from changes in extreme temperatures using dose–response functions for the relationship between temperature and labor from Graff Zivin and Neidell (2014).8f2308d0-7a25-4c47-82e0-cb9196f1de8b Under RCP8.5, almost 2 billion labor hours are projected to be lost annually by 2090 from the impacts of extreme heat and cold, costing an estimated $160 billion in lost wages. The Southeastbbca6337-718b-4289-b6e7-0a2f6c1cb8f1^,62152261-5dbb-4723-9506-ef63053863dd and Southern Plains are projected to experience high impacts, with labor productivity in high-risk sectors projected to decline by 3%. Some counties in Texas and Florida are projected to experience more than 6% losses in annual labor hours by the end of the century.0b30f1ab-e4c4-4837-aa8b-0e19faccdb94^,6e83fde3-5f98-4fd1-ae2c-d11aced414ac

Vector-borne disease: Belova et al. (2017)4308e866-5976-4181-8102-24b521ff4033 and the EPA (2017)0b30f1ab-e4c4-4837-aa8b-0e19faccdb94 define health impact functions from regional associations between temperatures and the probability of above-average West Nile neuroinvasive disease (WNND) incidence to estimate county-level expected WNND incidence rates for a 1995 reference period (1986–2005) and two future years (2050: 2040–2059 and 2090: 2080–2099) using temperature data from five GCMs. Annual national cases of WNND are projected to more than double by 2050 due to increasing temperatures, resulting in approximately $1 billion per year in hospitalization costs and premature deaths. In 2090, an additional 3,300 annual cases are projected under RCP8.5, with $3.3 billion per year in costs. Greenhouse gas emission reductions under RCP4.5 could avoid approximately half these cases and costs.

Water quality: Chapra et al. (2017)28077cd1-c29f-48ae-a068-2cdcef880807 and the EPA (2017)0b30f1ab-e4c4-4837-aa8b-0e19faccdb94 evaluate the biophysical impacts of climate change on the occurrence of cyanobacterial harmful algal blooms in the contiguous United States using models that project rainfall runoff, water demand, water resources systems, water quality, and algal growth. In 2090, warming under RCP8.5 is projected to increase the length of time that recreational waters have concentrations of harmful algal blooms (cyanobacteria) above the recommended public health threshold by one month annually; greenhouse gas emissions under RCP4.5 could reduce this by two weeks.

Food safety and nutrition: There is limited evidence quantifying specific health outcomes or economic impacts of reduced food safety and nutrition.

New information and remaining uncertainties:

While projections consistently indicate that changes in climate are expected to have negative health consequences, quantifying specific health outcomes (for example, number of cases, number of premature deaths) remains challenging, as noted in Key Message 1. Economic estimates only partially capture and monetize impacts across each health topic area, which means that damage costs are likely to be an undervaluation of the actual health impacts that would occur under any given scenario. Economic estimates in this chapter do not include costs to the healthcare system.

Assessment of confidence based on evidence:

There is a high confidence that a reduction in greenhouse gas emissions would benefit the health of Americans. There is medium confidence that reduced greenhouse gas emissions under RCP4.5 compared to RCP8.5 will likely reduce lost labor hours by almost half and avoid thousands of premature deaths and illnesses projected each year from climate impacts on extreme heat, ozone and aeroallergen levels (Ch. 13: Air Quality), and West Nile neuroinvasive disease. There is medium confidence that the economic benefits of greenhouse gas emissions reductions in the health sector could likely be on the order of hundreds of billions of dollars each year by the end of the century. Including avoided or reduced benefits of risks that are difficult to quantify, such as mental health or long-term health consequences, would increase these estimates.

Provenance

This finding was derived from scenario rcp_4_5
This finding was derived from scenario rcp_8_5