01 - 473 Health Effects of Climate Change

473 Health Effects of Climate Change

Disorders Associated with Environmental Exposures PART 15 Eugene Richardson, Maxine A. Burkett

Health Effects of

Climate Change Climate change refers to the effects of accumulated greenhouse gases (GHGs) in the atmosphere on long-term weather patterns. Anthropo­ genic emissions—in particular from the burning of fossil fuels and land conversion—have increased mean global temperatures by approxi­ mately 1.1° Celsius above preindustrial levels. Extreme weather events, including heatwaves and ‘natural disasters’ (e.g., wildfires, droughts, and floods) are becoming more frequent and lead to resource scarcity (including access to safe drinking water and food), increased envi­ ronmental pollution and degradation, violent conflict, and precarious migration. The climate crisis thus has direct consequences for human health (Fig. 473-1), the practice of medicine, and the stability of health care systems and as such represents a health emergency. See Chap. 474 for an overview of climate science. EFFECTS OF CLIMATE CHANGE

ON HEALTH The World Health Organization predicts that between 2030 and 2050, there will be an additional 250,000 deaths from undernutrition, malaria, diarrhea, and heat stress alone (Chap. 474). As with much of the global burden of disease, this increase in mortality will be dis­ proportionately borne by low- and middle-income countries (LMICs) whose health infrastructures have been weakened by neocolonialism and structural adjustment. Within wealthier countries such as the United States, climate change will amplify existing health disparities between white people and black, Indigenous, and Latinx populations. Impact of Climate Change on Human Health Injuries, fatalities, mental health impacts Asthma, cardiovascular disease Heat-related illness and death, cardiovascular failure Extreme Heat s g n si Environmental Degradation Forced migration, civil conflict, mental health impacts a Water Quality Impacts Water and Food Supply Impacts Malnutrition, diarrheal disease FIGURE 473-1  Climate change impacts a wide range of health outcomes. This figure illustrates the most significant climate change impacts (rising temperatures, more extreme weather, rising sea levels, and increasing carbon dioxide levels), their effect on exposures, and the subsequent health outcomes that can result from these changes in exposures. (Source: https://www.cdc.gov/climateandhealth/effects/default.htm.)

■ ■AIR POLLUTION AND SYNERGISTIC EFFECTS Asthma and Other Respiratory Ailments  Climate change exacerbates the negative health effects of harmful air pollutants (e.g., particulate matter, ozone, sulfur dioxide, and nitrogen dioxide). While increases in fine particulate matter (<2.5 microns—PM2.5) are a func­ tion of wildfires and the burning of fossil fuels, the latter is the pre­ dominate driver of anthropogenic climate change. Exposure to ambient air pollution and/or indoor air pollution is estimated to cause 7 million premature deaths worldwide per year, making it the largest global envi­ ronmental risk factor for reversible death and disability (see Chap. 300 for an overview). Notably, air pollution from coal-burning power plants is associated with double the mortality risk when compared with other sources of PM2.5. By increasing ground-level ozone and/or particulate matter con­ centrations in some regions, the higher temperatures associated with climate change will directly increase the global burden and severity of asthma (Chap. 298), the respiratory effects of allergies (Chap. 363), rhi­ nosinusitis, chronic obstructive pulmonary disease (COPD), respira­ tory tract infections, interstitial lung disease, and lung cancer, resulting in increased hospital admissions and premature death. Figure 473-2 illustrates potential pathophysiologic mechanisms by which this may occur. Cardiovascular Disease  Cardiovascular (CV) complications of climate change share similar mechanisms with climate-sensitive respiratory disease. Concentrations of PM2.5 are the most important environmental risk factor for myocardial infarction, cerebrovascular disease, heart failure, hypertension, diabetes mellitus, arrhythmias, and venous thromboembolism. Studies have shown that the relative risk of acute CV events is increased 1–3% in the setting of short-term elevations of PM2.5. Longer-term exposures convey an amplified risk (~10%), which is partially attributable to the exacerbation of chronic conditions (e.g., hypertension and diabetes). This holds true for areas with low mean Malaria, dengue, encephalitis, hantavirus, Rift Valley fever, Lyme disease, chikungunya, West Nile virus Severe Weather Air Pollution

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Ultrafine particles ROS Ca2+ TNF-α Activated T-cell MAPK NFKB AP-1 Cell barrier damage Innate immunity Adaptive immunity Oxidative stress Lung diseases Asthma, COPD, Lung cancer, Interstitial lung diseases, Lung fibrosis, Acute lung injury FIGURE 473-2  Mechanisms of ultrafine particle–induced respiratory health effects. (Reproduced from GD Leikauf et al: Mechanisms of ultrafine particleinduced respiratory health effects. Exp Mol Med 52:329, 2020.) concentrations of PM2.5 (i.e., where risk is determined by recurring short-term elevations). The biologic pathways whereby PM2.5 promotes these complications are complex and multifactorial (Fig. 473-3). PART 15 Disorders Associated with Environmental Exposures For clinicians, there are subtle management strategies to bear in mind for climate-sensitive CV disease. For example, in new heart fail­ ure patients, prescribers should be judicious about starting diuretics (especially diuretic-angiotensin–converting enzyme [ACE] inhibitor combinations) before the summer months or in areas with increased heatwaves in order to avoid exacerbating dehydration or heat-related illness. These patients may also benefit from increasing potassium uptake. Figure 473-4 presents personal- and local-level interventions to reduce climate-sensitive disease associated with air pollution. Pregnancy  Women exposed to high temperatures and air pollution may be more likely to experience serious adverse pregnancy outcomes. A systematic review of studies across diverse U.S. populations found a statistically significant association of PM2.5, ozone, and heat exposure with preterm birth, low birth weight at term, and stillbirth. As these environmental exposures become more common with climate change, an increased incidence of these complications is likely. Potential pathophysiologic mechanisms for these outcomes are mul­ tifactorial: preterm birth may result from hematogenous transport of inhaled PM2.5 and varied noxious chemicals and subsequent systemic inflammation or perturbation of the autonomic nervous system; low birth weight could be caused by the cumulative effect of alterations in maternal cardiac, pulmonary, and renal function, placental inflamma­ tion, and direct exposure to oxidative stress; and stillbirth may involve derangements in oxygen transport, DNA damage, and direct placental injury. Extreme heat events may lead to adverse pregnancy outcomes through dehydration and subsequent alterations in thermoregulation, blood viscosity, uterine blood flow, placental-fetal exchange, amniotic fluid volume, and hormone release (e.g., prostaglandin or oxytocin). These risks are disproportionately borne by black mothers. Thus, failure to reduce air pollution to the World Health Organization guide­ line level of 10 μg/m3 compounds structural racism. ■ ■HEAT-RELATED ILLNESSES Renal Disease  Various populations of agricultural workers who labor in hot climates around the world have been noted to suffer from chronic kidney disease (CKD), even those without common risk fac­ tors such as diabetes mellitus, hypertension, glomerular disease, or HIV. Although the cause has not been identified, potential mechanisms

include genetic polymorphisms, nephrotoxicity secondary to agro­ chemicals or heavy metals, and heat-associated injury (Fig. 473-5). Heat Exhaustion and Heatstroke  Please see Chap. 478 for an overview of heat-related illnesses. These include heat cramps, heat exhaustion, and heatstroke and can be expected to increase in incidence as temperatures rise. Certain communities suffer from sig­ nificant peaks in average temperature resulting from the urban heat island effect, which in the United States is related to policies such as redlining, racial covenants, and strategic underinvestment in neighbor­ hoods segregated through such policies. Possible preventive measures include developing clear heatwave strategies and establishing early warning systems, mapping vulnerable populations, enhancing green space, and providing cool-down zones. It is important that clinicians provide guidance about heat-related illnesses prior to the start of sum­ mer because waiting for heat warnings will not obviate risk. Medication storage is an issue, especially for those that are carried by patients (e.g., epinephrine injections, naloxone, insulin). There are some data to sug­ gest that exposure to extreme heat (e.g., leaving an albuterol inhaler in a vehicle on a hot day) can impair delivery mechanisms, degrade active ingredients of the medication, or cause inhalers to explode. ■ ■NATURAL DISASTERS, COASTAL FLOODING,

AND DISPLACEMENT Injury and Trauma  While models predict fewer cyclones and hur­ ricanes in a warmer late-twenty-first-century climate, they do forecast events of higher average intensity, precipitation, and the number and occurrence days of very intense category 4 and 5 storms (Fig. 473-6). Such natural disasters would be expected to result in injuries and trauma seen in contemporary storms of high intensity (albeit with higher frequency), but there are other ways climate change will affect the inci­ dence of physical trauma. Studies have shown associations between anomalously warm tem­ peratures and increased deaths from drownings (from people swim­ ming longer and more frequently), transportation accidents (driving performance worsens at higher temperatures and traffic increases), and assaults (potentially from increased alcohol consumption and illicit drug use). These deaths were partly offset by decreased falls, especially among the elderly, in warmer years. In addition, as more than half the world’s population lives within 60 km of the ocean, rising sea levels will destroy homes, medical infra­ structure, and other essential services, including sewage treatment systems and drinking water supplies. In concert with climate impacts such as extreme heat and lack of freshwater, subsequent displacement and migration will lead to increased mental illness, food insecurity, and communicable disease. Finally, extreme sudden-onset events can affect the availability of medications through medical supply chain disruptions. Loss of electric­ ity during intense storms can also compromise vaccination programs and the availability of needed medications. For example, in 2024, Hur­ ricane Helene interrupted the production of essential parenteral drug products and intravenous (IV) fluids manufactured in North Carolina, resulting in nationwide shortages in the United States. Providers should ensure that patients with electricity-dependent medical devices have a reasonable contingency plan in case of power outages while noting that climate-related displacements can interrupt patients’ access to medica­ tions for chronic diseases and limit access to clinical care in general. Mental Illness  As of 2022, an estimated 108.4 million people (i.e., 1.4% of humanity) were forcibly displaced from their homes, mainly on account of violent conflict. It is expected that millions more will be displaced in response to the effects of climate change. This has ramifications for mental health (as do natural disasters) where resul­ tant psychosocial stress can lead to an increased incidence of anxiety, depression, and posttraumatic stress disorder (PTSD). Increased tem­ peratures have also been found to be associated with higher rates of suicide and domestic violence. Lastly, regarding clinical practice, many psychoactive prescription drugs can interfere with thermoregulation; their use therefore confers added risk during extreme heat events.

CNS Inflammation Neural Reflex Arc Direct Translocation Biologic Intermediates Autonomic Imbalance Endothelial Dysfunction Adhesion Molecules ↑ eNOS Uncoupling Impaired EPC Function ↑ NADPH Oxidase ↑ Proliferation ↑ Vasoconstriction ↓ Vasodilation ↑ Superoxide + ↑ Nitric Oxide ↑ Inflammation ↑ Peroxynitrite ↑ ROS and RNS Low-grade Inflammation Cardiometabolic Disease FIGURE 473-3  Biologic pathways whereby PM2.5 promotes cardiovascular events. (Reproduced with permission from S Rajagopalan: Air pollution and cardiovascular disease: JACC state-of-the-art review. J Am Coll Cardiol 72:2054, 2018.) ■ ■FOOD SECURITY AND OCEAN RESOURCES Malnutrition  Climate change threatens food and nutritional secu­ rity through decreased crop yields in the setting of changes in precipi­ tation, desertification, severe weather events, temperature extremes, GHG emissions, ocean warming and acidification, coastal inundation affecting dryland agriculture and aquaculture, and increasing competi­ tion from weeds and pests (Fig. 473-7). Livestock and fish production are also projected to decline. For many, food will be less available, less nutritious, and more expensive. As chronic noncommunicable diseases, both undernutrition (Chap. 345) and obesity (Chap. 413)—which affect nearly 3 billion

Air Pollution Oxidative Stress Systemic Inflammation Thrombotic Pathways HPA Axis Activation CHAPTER 473 Platelet Activation ↑ TLR Macrophage Health Effects of Climate Change Thrombosis Activated Endothelium ↑ Fibrinogen MMP-2 MMP-9 ↑ Inflammatory cytokine ↑ NF-κB Smooth Muscle Proliferation ↑ people worldwide—share common drivers with climate change. Cur­ rent dietary practices (through land conversion and overconsumption of ruminant meats) contribute to excess GHGs, decreases in biodiver­ sity, and depletion of water supplies. Variable rainfall and increased flooding, which can contaminate freshwater supplies, will make water security a defining challenge of this century. Plant-based diets have the potential to decrease GHG emissions; improve food security in LMICs; reduce mortality from stroke, type 2 diabetes mellitus, coronary heart disease, and cancer by 6–10%; and reduce diet-related GHGs by 29–70% by 2050 compared with a refer­ ence diet (Fig. 473-8).

• Switch coal-fired power plants to low-polluting renewable energy sources such as wind, tidal, geothermal, and solar. Shifting to clean fuels • Promote use of low-emission and zero-emission vehicles. Reduce sulfur content of motor fuels. Restrict trucks from city centers, encourage active transport (walking and cycling). SOCIETAL AND GOVERNMENTAL INTERVENTIONS PERSONAL INTERVENTIONS Transportation reform Reduce traffic emission(s) • Diesel particle traps, catalytic converters, alternative fuels (natural gas, electric cars) • Land-use assessment, minimum distances between sources and people, relocation of traffic sources (including major trafficked roads), avoidance of mixed-use areas (industrial-residential) Urban landscape reform • Revenues raised through taxes can be directed to pollution control. Emissions trading programs compensate companies who adhere to controls through credits that can be traded akin to carbon credits Emission trading programs Redirection of science and funding • Modifying priorities of climate change mitigation investments to a focus on near-term health co-benefits. Focus on the imminent near-term danger of health effects of air pollution. • Publicity and awareness campaigns through local data on air pollution within cities, counties Empowering civil society • Hard-hitting media campaigns akin to smoking on media to mitigate lobbying by industries involved in power and automobiles Governmental and NGOled publicity Face masks and air purifiers • Wearing face masks and installing air purifiers in homes PART 15 Disorders Associated with Environmental Exposures • Avoid commutes during rush hour Reduce in-traffic exposures Reduce in-home penetration of outdoor air pollution • Indoor air purifiers and closing windows; air conditioners Lifestyle changes and preventive medicine • Exercise and healthy diet • Preventive medications and screening programs FIGURE 473-4  Social ecological interventions to reduce exposures or susceptibility to air pollution. (Reproduced with permission from S Rajagopalan: Air pollution and cardiovascular disease: JACC state-of-the-art review. J Am Coll Cardiol 72:2054, 2018.) Dehydration and extracellular volume loss Hyperosmolarity (increased vasopressin and aldose reductase) Crystalluria (urate) Rhabdomyolysis Toxins and toxicants Pesticides Heavy metals Silica Other FIGURE 473-5  Possible mechanisms for the development of chronic kidney disease of unknown cause in agricultural communities. (Adapted from RJ Johnson et al: Chronic kidney disease of unknown cause in agricultural communities. N Engl J Med 380:1843, 2019. Copyright © 2019 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.)

Heat exposure lncreased core temperature Proximal tubular uptake of toxin from low renal blood flow Primary organ dysfunction Kidney inflammation and tubular injury Mesoamerican nephropathy

Present-day simulation

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A RCP4.5 late 21st century projection

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B Late 21st century minus present-day

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C FIGURE 473-6  Simulated occurrence of all tropical storms (tropical cyclones with winds exceeding 17.5 m s−1) for (A) present-day or (B) late-twenty-first-century (RCP4.5; CMIP5 multimodel ensemble) conditions; unit: storms per decade. Simulated tropical cyclone tracks were obtained using the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model to resimulate (at higher resolution) the tropical cyclone cases originally obtained from the HiRAM C180 global mode. Occurrence refers to the number of days, over a 20-year period, in which a storm exceeding 17.5 m s−1 intensity was centered within the 10° × 10° grid region. (C) Difference in occurrence rate between latetwenty-first century and present day [(B) minus (A)]. White regions are regions where no tropical storms occurred in the simulations [in (A) and (B)] or where the difference between the experiments is zero [in (C)]. (From TR Knutson et al: Global projections of intense tropical cyclone activity for the late twenty-first century from dynamical downscaling of CMIP5/RCP4.5 scenarios. J Clim 28:7203, 2015 © American Meteorological Society. Used with permission.) Average temperature & weather variability Air humidity Precipitation level Greenhouse gas emissions (GHG) Evapotranspiration rate Infectious diseases Climate/ weather Evaporation rate Precipitation index Soil moisture fertilizer Food crop yields Soil quality Food prices Labor capacity Food affordability Household income FIGURE 473-7  Complex pathways from climate/weather variability to undernutrition in subsistence farming households. The factors involved in and the probable impacts of weather variables on crop yields (blue arrows) and of food crop yields on undernutrition (red arrows). (Reproduced with permission from RK Phalkey et al: Climate change impacts on childhood undernutrition. Proc Natl Acad Sci USA 112:E4522, 2015.)

–20 –40 –60 –80 –100 –120 CHAPTER 473 Health Effects of Climate Change Health care Utilization rate Child undernutrion Rate of child malnutrition Household access to food Rate of malnutritionrelated child mortality Children’s quality of life Per capita food availability consumption & utilization Mothers’ quality of life Malnourished mothers Rate of maternal malnutrition Rate of malnutritionrelated maternal mortality