finding 25.7 : key-message-25-7

Heat-associated deaths and illnesses, vulnerabilities to chronic disease, and other health risks to people in the Southwest result from increases in extreme heat, poor air quality, and conditions that foster pathogen growth and spread (high confidence). Improving public health systems, community infrastructure, and personal health can reduce serious health risks under future climate change (medium confidence).

This finding is from chapter 25 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.

Description of evidence base:

Strong evidence and good agreement among multiple sources and lines of evidence exist, indicating that the Southwest regional temperature may increase, snowpack may decline, soil moisture may decrease, and drought may be prolonged.ba57f86f-c42f-4bba-83f6-676d6875c176,29960c69-6168-4fb0-9af0-d50bdd91acd3,acbb7b12-c119-4c42-8a80-c2555964db4c,89e08a41-6091-45fa-a92e-6168a90a8151,4ca5a43c-5fbe-4cb0-8a7d-7ee3acafd7c0,d06fadc5-a5e3-463c-85d0-f78c07c6ade9,65135859-7587-4f65-b2b3-8ca4d5b8ce49,a29b612b-8c28-4c93-9c18-19314babce89,4fbaaa13-99d2-43df-93db-2be546f18892

Exposure to hotter temperatures and extreme heat events, partly a manifestation of human-caused climate change, already led to heat-associated deaths and illnesses in heat waves in Arizona and California in the early and mid-2000s.b3e00a14-a876-44fa-9c1f-836bd53a7f69,60c98535-ad37-43fa-b0fd-e7c850782d13,7ca0e947-163a-46f3-9274-cea209b94510,eaabcdba-02ea-478b-899b-d0924862128b,5f4db33c-1c7e-4129-9438-e5d8c9d589e4,22344c1d-cee2-4f9d-91c0-60ceb6e9ca57,5f587662-8664-420f-8045-196e2bb7ec0d,d3a3ca44-1e49-41ee-9063-dc1be22dec3c,303cc526-6398-4a92-9f79-ec1f8a1d92d1

Good agreement exists among models that most of the Southwest may become more arid, due to the effect of increasing temperatures on snow, evaporation, and soil moisture.4ca5a43c-5fbe-4cb0-8a7d-7ee3acafd7c0,ed70fd44-147d-4ffa-ab1b-68451bd1d335,b4678125-72a3-4c14-8159-b5c18ca2b38b,a53545b0-5b89-456f-ab35-1e11d6f78c8c Projections also indicate that flood-causing atmospheric rivers may become more moist, frequent, and intensea2470cdb-4b8f-4ed6-8c5f-38cd301053a2,f0d25167-e8ea-435d-838b-44d0f8be9dc9,f0a98dc9-f5c5-4fa0-a90c-7791e2809744 and that intense daily precipitation may increase in frequency.e8089a19-413e-4bc5-8c4a-7610399e268c,8785e73d-2258-47f6-b4f5-a79b6ac5ce25 Models project declines in future runoff of key Southwest rivers, such as the Colorado, due chiefly to the effects of increased temperature on soil moisture and snowpack.a42c4f5e-f16b-4196-af05-61f117e0491d,df25e033-b388-4aab-b7a4-00d6a9ef3e7e,a464ea68-c53b-4af4-8f29-d063dbc4c026

Strong evidence exists of the effects of extreme heat on public health in the region (e.g., Knowlton et al. 2009, Oleson et al. 2015, Wilhelmi et al. 20047ca0e947-163a-46f3-9274-cea209b94510,a26de55c-92a2-4a6e-bd72-8eee0cdcc4af,d8c02480-fd9d-40a0-96e2-8432fc460329) and for reasonable projections of future deaths and costs of lost labor productivity due to enhanced future episodes of extreme heat. Factors that predict a person will be at increased risk include being confined to bed, not leaving home daily, and being unable to care for oneself;e7927819-0782-42ff-a491-6e125f61600e various general indicators of being socially isolated (such as living alone, the presence of or frequency of social contacts, or being isolated linguistically);e7927819-0782-42ff-a491-6e125f61600e,cc49dc7d-d481-4103-a681-a17fe17d35c2,be822c05-64af-4f62-b17a-1cf5fc3a0cf7,53b9906c-e4bf-4190-8ce7-73022280cba6 and persons who are socioeconomically disadvantaged.e7927819-0782-42ff-a491-6e125f61600e,cc49dc7d-d481-4103-a681-a17fe17d35c2,be822c05-64af-4f62-b17a-1cf5fc3a0cf7,53b9906c-e4bf-4190-8ce7-73022280cba6 Dehydration in general and dehydration associated with medications (neurological and non-neurological) that impair thermoregulation or thirst regulation were also associated with elevated risk of mortality during the 2003 heat wave in France.114cd0b9-5577-4c58-b5b1-24c822dd4ad7 The role of prescription medications in altering the risk for heat-associated illness or death is of growing interest and concern.919be859-ff09-4c3a-89c8-72433add7e42 This issue is more important as chronic diseases become more prevalent and more people take prescription drugs.

Given the proportion of the U.S. population in the Southwest, a disproportionate number of West Nile virus, plague, hantavirus pulmonary syndrome, and Valley fever cases occur in the region.d8bd2def-be9b-47e3-84de-199bcd26c31d,3d9b7135-b89c-4a20-a660-13217078a6ee West Nile virus transmission is projected to shift to the north under climate change, and areas where the mosquitoes that carry this virus are present may see increased abundances.75a73642-5567-4768-810c-ba889b2d38a4,132133f3-1705-42ed-b505-8ccbaa497968,d7564231-5587-4333-abe1-3caef085fd98 The mosquito species that carry Zika and chikungunya are established in parts of the region, but mosquito-borne transmission has only been observed in Puerto Rico, the U.S. Virgin Islands, Florida, and Texas (Ch. 14: Human Health).

Overall, the Southwest is ill-prepared to absorb the additional patient load that would accompany climate change associated disasters.e523f9c0-56f9-44ff-b2d9-7debec2a19d0 The American College of Emergency Physicians assigned an overall emergency care grade of C or C+ to three of the six Southwest states, with the others receiving poorer grades, and four of the six states received an F grade for access to emergency care.e523f9c0-56f9-44ff-b2d9-7debec2a19d0

New information and remaining uncertainties:

Uncertainties in the climate and hydrologic drivers of regional changes affecting public health include 1) differences in projections from multiple GCMs and associated uncertainties related to regional downscaling methods, 2) variability in projections of extreme precipitation, 3) uncertainties in summer and fall precipitation projections for the region,e8089a19-413e-4bc5-8c4a-7610399e268c and 4) uncertainties in models that project occurrence and levels of climate-sensitive exposures that are known to impact public health, such as local and regional ozone air pollution, particulate air pollution (for example, increases from wildfire emissions or reductions from advancements in vehicle emissions control technology), or occurrence and exposure to toxins or pathogens.

Studies of non-fatal illnesses using healthcare services data can yield critical insights different from those one can derive from death data. Most studies of heat impacts on health have focused on deaths rather than nonfatal illnesses. This is primarily because hospitalization and emergency department data, compared with death certificate data, are not as available or uniform across locations, and when they are available it can be difficult to access them due to concerns for patient confidentiality. Ongoing enhancements to electronic medical records technology and adoption across the healthcare services sector will potentially address those limitations in the near future and will provide invaluable data resources to identify and adopt prevention strategies that reduce the vulnerability of patients and populations to the adverse effects of climate-sensitive exposures.

More recent work focusing on the more deadly neuroinvasive West Nile virus indicates that regionally, the central and southern parts of the country may experience increasing cost from this vector-borne disease in the future.0b30f1ab-e4c4-4837-aa8b-0e19faccdb94,4308e866-5976-4181-8102-24b521ff4033 The lack of a statistical association between temperature and West Nile virus diagnoses in the Southwest may be because extreme temperatures in some locations rise above the survival thresholds for vectors, thereby reducing mosquito abundance7a2ecd14-047d-4b75-8fb8-939f99e23c08,d8fa9745-f20f-4681-8eec-586cc6b8d369 and disease transmission.b3a14272-c3f4-4226-a196-afc0d0992306 Additionally, because the data for diseases like Valley fever are limited to cases, rather than exposures, the link to climate change is not clear.b262f5a3-6d59-4902-ba8e-04427593dabd,cea75900-8720-40d7-9195-93bb86f46c4b

While improvements to individual health and to clinical and community infrastructure are highly likely to 1) improve physical capacity to adapt to climate effects, 2) diminish the overall impacts on population health, and 3) increase societal capacity to respond quickly to dampen the effects of long-term and emergency responses,46b92d0e-f9f2-4b12-8b9e-8c27d6a4b9da,1d09c643-e588-4d94-8f85-e786dabb1f18,0e186af3-bf5b-49ae-82cc-cf1a1a5a7c25 other factors also influence adaptive capacity, adding considerable uncertainty. For example, many factors influence the observed number of West Nile virus cases including available habitat, human prevention and control efforts, and recent history of cases in a given area.132133f3-1705-42ed-b505-8ccbaa497968,110b6896-b3e8-4af4-9c57-70cd5dcc49b0,48041d66-fd27-4cf6-8155-9a74d3d664dd,fcae8bc8-4bef-454f-9093-90952248ed79

Assessment of confidence based on evidence:

Evaluation of confidence levels for the assessment of the type and magnitude of observed or projected public health and clinical impacts was based on the strength of evidence underlying the answers to three primary questions:

  1. What characteristics of the region’s historical climate and weather patterns translate directly (for example, extreme heat) or indirectly (for example, higher temperatures fostering ozone formation or the growth and spread of pathogens and vectors) to exposures associated with observed human health risks that are unique to or overrepresented in the Southwest?

  1. Does recent historical evidence indicate that climate and weather patterns have changed, or do climate models project changes over the 21st century, thereby increasing the risk of human exposures and health impacts evaluated under question 1?

  2. What are the determinants of individual and population vulnerability that increase or decrease the risk of an adverse health outcome or affect adaptive capacity? These include factors that affect a) biological susceptibility, b) physical environment and exposure characteristics, and c) social, behavioral, or economic factors.

To the extent possible, the evaluation recognized and accounted for the complex interconnections among these factors, the fact that their relative importance may differ across geographic and temporal scales, and the combined uncertainties of evidence from multiple disciplines (for example, health sciences, climatology, and social or behavioral sciences) that can vary substantially.

The information revealed by answering those questions, gives high confidence that extreme heat will be the dominant driver of exposures that pose the greatest health risks in the Southwest—including direct effects of heat on individuals and indirect effects of heat on air pollution levels. Due to the uncertainties related to the frequency and intensity of human exposures and related to impacts on essential ecosystem services under projected climate change, the statement “Improving public health systems, community infrastructure, and personal health can reduce serious health risks under future climate change” is made with medium confidence. Nevertheless, clinical and public health policy effectiveness assessments show that such improvements can reduce the burden of disease and health risks associated with environmental exposures.

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

References :

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