Increased heat wave intensity and frequency, increased humidity, degraded air quality, and reduced water quality will increase public health risks.

This finding is from chapter 18 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: The assessment process for the Midwest Region began with a workshop was that was held July 25, 2011, in Ann Arbor, Michigan. Ten participants discussed the scope and authors for a foundational Technical Input Report (TIR) report entitled “Midwest Technical Input Report.”2626b5ca-ec04-4e41-8405-9f582c779a7a The report, which consisted of nearly 240 pages of text organized into 13 chapters, was assembled by 23 authors representing governmental agencies, non-governmental organizations (NGOs), tribes, and other entities. The Chapter Author Team engaged in multiple technical discussions via teleconferences that permitted a careful review of the foundational TIR2626b5ca-ec04-4e41-8405-9f582c779a7a and of approximately 45 additional technical inputs provided by the public, as well as the other published literature, and professional judgment. The Chapter Author Team convened teleconferences and exchanged extensive emails to define the scope of the chapter for their expert deliberation of input materials and to generate the chapter text and figures. Each expert drafted key messages, initial text and figure drafts and traceable accounts that pertained to their individual fields of expertise. These materials were then extensively discussed by the Author Team and were approved by the Chapter Team members.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in the Technical Input Report.2626b5ca-ec04-4e41-8405-9f582c779a7a Technical inputs on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. Evidence for extreme weather such as heat waves across the U.S. are discussed in Chapter 2 (Our Changing Climate, Key Message 7) and its Traceable Accounts. Specific details for the Midwest are in “Climate Trends and Scenarios for the U.S. National Climate Assessment”95f2ea7d-12e3-4ed5-9247-7cf139db91a9 with its references. A recent bookb228ac0d-7bf9-4391-99e7-5c598b9ce55e also contains chapters detailing the most current evidence for the region. Heat waves: The occurrence of heat waves in the recent past has been well-documented,cd02cc8f-9ba1-4ce5-8283-b479b0374d33 1e5da375-51dd-4e29-8fe3-0d9e164b7856 9a70a3f4-3c60-4a8a-8cc9-bf5d7e112c12 as have health outcomes (particularly with regards to mortality). Projections of thermal regimes indicate increased frequency of periods with high air temperatures (and high apparent temperatures, which are a function of both air temperature and humidity). These projections are relatively robust and consistent between studies. Humidity: Evidence on observed and projected increased humidity can be found in a recent study.9a70a3f4-3c60-4a8a-8cc9-bf5d7e112c12 Air quality: In 2008, in the region containing North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin, Illinois, Michigan, Indiana, and Ohio, over 26 million people lived in counties that failed the National Ambient Air Quality Standards (NAAQS) for PM2.5 (particles with diameter below 2.5 microns), and over 24 million lived in counties that failed the NAAQS for ozone (O3).cd02cc8f-9ba1-4ce5-8283-b479b0374d33 Because not all counties have air quality measurement stations in place, these data must be considered a lower bound on the actual number of counties that violate the NAAQS. Given that the NAAQS were designed principally with the goal of protecting human health, failure to meet these standards implies a significant fraction of the population live in counties characterized by air quality that is harmful to human health. While only relatively few studies have sought to make detailed air quality projections for the future, those that havecd02cc8f-9ba1-4ce5-8283-b479b0374d33 generally indicate declining air quality (see uncertainties below). Water quality: The EPA estimates there are more than 800 billion gallons of untreated combined sewage released into the nation’s waters annually.5a66bdda-d5f3-4eb0-83d1-64cb86216182 Combined sewers are designed to capture both sanitary sewage and stormwater. Combined sewer overflows lead to discharge of untreated sewage as a result of precipitation events, and can threaten human health. While not all urban areas within the Midwest have combined sewers for delivery to wastewater treatment plants, many do (for example, Chicago and Milwaukee), and such systems are vulnerable to combined sewer overflows during extreme precipitation events. Given projected increases in the frequency and intensity of extreme precipitation events in the Midwest (Chapter 2: Our Changing Climate, Key Message 6),030e3539-a620-441c-adb6-042db1a3fa6e it appears that sewer overflow will continue to constitute a significant current health threat and a critical source of climate change vulnerability for major urban areas within the Midwest.

New information and remaining uncertainties: Key issues (uncertainties) are: Human health outcomes are contingent on a large number of non-climate variables. For example, morbidity and mortality outcomes of extreme heat are strongly determined by a) housing stock and access to air-conditioning in residences; b) existence and efficacy of heat wave warning and response plans (for example, foreign-language-appropriate communications and transit plans to public cooling centers, especially for the elderly); and c) co-stressors (for example, air pollution). Further, heat stress is dictated by apparent temperature, which is a function of both air temperature and humidity. Urban heat islands tend to exacerbate elevated temperatures and are largely determined by urban land use and human-caused heat emissions. Urban heat island reduction plans (for example, planted green roofs) represent one ongoing intervention. Nevertheless, the occurrence of extreme heat indices will increase under all climate scenarios. Thus, in the absence of policies to reduce heat-related illness/death, these impacts will increase in the future. Air quality is a complex function not only of physical meteorology but emissions of air pollutants and precursor species. However, since most chemical reactions are enhanced by warmer temperatures, as are many air pollutant emissions, warmer temperatures may lead to worsening of air quality, particularly with respect to tropospheric ozone (see Ch. 9: Human Health). Changes in humidity are more difficult to project but may amplify the increase in heat stress due to rising temperatures alone.9a70a3f4-3c60-4a8a-8cc9-bf5d7e112c12 Combined sewer overflow is a major threat to water quality in some midwestern cities now. The tendency towards increased magnitude of extreme rain events (documented in the historical record and projected to continue in downscaling analyses) will cause an increased risk of waterborne disease outbreaks in the absence of infrastructure overhaul. However, mitigation actions are available, and the changing structure of cities (for example, reducing impervious surfaces) may offset the impact of the changing climate.

Assessment of confidence based on evidence: In the absence of concerted efforts to reduce the threats posed by heat waves, increased humidity, degraded air quality and degraded water quality, climate change will increase the health risks associated with these phenomena. However, these projections are contingent on underlying assumptions regarding socioeconomic conditions and demographic trends in the region. Confidence is therefore high regarding this key message.

References :

• Climate Change in the Midwest: Impacts, Risks, Vulnerability, and Adaptation (9a70a3f4)
• (2626b5ca)
• Regional Climate Trends and Scenarios for the U.S. National Climate Assessment: Part 3. Climate of the Midwest U.S. NOAA Technical Report NESDIS 142-3 (95f2ea7d)
• Climate Change in the Midwest: Impacts, Risks, Vulnerability, and Adaptation (b228ac0d)
• Climate Change in the Midwest: Impacts, Risks, Vulnerability, and Adaptation (cd02cc8f)
• Climate Change in the Midwest: Impacts, Risks, Vulnerability, and Adaptation (1e5da375)
• Distribution and Fate of Escherichia coli in Lake Michigan Following Contamination with Urban Stormwater and Combined Sewer Overflows (5a66bdda)
• Climate Change and Waterborne Disease Risk in the Great Lakes Region of the U.S. (030e3539)