14.4 Climate Change and Population Health

Oceanic Impact

Encompassing approximately 70 percent of the Earth’s surface, oceans are vital to planetary health. Oceans absorb both carbon dioxide (CO₂) and heat, slowing the progression of atmospheric global warming. However, this absorption transforms the ocean’s chemistry and temperature, leading to ocean acidification and sea level rise, shifting currents, and impacting marine life and biodiversity (EPA, 2023h). The oceans have absorbed about 28 percent of annual anthropogenic CO₂ emissions and captured approximately 90 percent of the planet’s heat generated by greenhouse gases (EPA, 2023i). As a buffer, the oceans have offset climate impacts. However, as the ocean’s acidity and temperatures rise, its capacity to absorb CO₂ from the atmosphere diminishes, potentially hampering its ability to moderate climate change. Furthermore, the increased absorption of heat leads to higher sea surface temperatures and sea levels (EPA, 2023i). Climate change–induced shifts in ocean temperatures and currents are altering global climate patterns. For instance, warmer waters fuel stronger tropical storms, resulting in flooding, property damage, environmental devastation, and loss of life. Coastal communities are particularly susceptible to the impacts of rising sea levels and intensified storm surges (EPA, 2023d).

Increasing carbon levels are making the oceans more acidic, posing challenges for corals and shellfish, hindering their ability to construct skeletons and shells, and potentially reshaping the oceanic ecosystems’ biodiversity and productivity (EPA, 2023h). However, the impacts of climate change on ocean ecosystems are most severe in tropical and polar regions. In the tropics, ocean warming is leading to widespread coral bleaching, outbreaks of coral diseases, and the destruction of coral reefs, which provide food and shelter for numerous marine organisms and support coastal communities (NOAA, 2023b). In the Arctic, sea ice is melting, reducing habitats for marine mammals (EPA, 2023b). In Antarctica, warming has led to the collapse and shrinkage of ice shelves, changing patterns of wildlife behavior and threatening the ecosystem (EPA, 2023g). Melting ice and altered ocean currents raise sea levels, impact ocean circulation, and influence global weather patterns (EPA, 2023i).

Climate change has caused significant damage and progressively irreversible losses in terrestrial, freshwater, coastal, and marine ecosystems. The scope and intensity of these impacts surpass previous estimates. Climate change has deteriorated ecosystem structure and function, seasonal timing, resilience, and adaptive capacity. Globally, around half of assessed species have shifted toward the poles or higher elevations (Dawson, 2022). Local species losses have been driven by intensified heat, mass mortality on land and in oceans, and the disappearance of kelp forests (Rogers-Bennett & Catton, 2019). Although more gradual, processes like ocean acidification and rising sea levels are linked to climate change (EPA, 2023i). Some losses, like species extinctions, are irreversible. Other impacts, such as retreating glaciers and changes in mountain and Arctic ecosystems due to thaw, are nearing irreversibility (Intergovernmental Panel on Climate Change, 2019). The impact of climate change through time can be visualized using this time machine developed by NASA.

Extreme Weather

The impact of climate change is increasingly evident in the escalating intensity of tropical storms. The incidence of highly destructive U.S. hurricanes has tripled over the last century (Grinsted et al., 2019), with the prevalence of major hurricanes (Category 3 or above) in the Atlantic Ocean doubling since 1980 (Pfleiderer et al., 2022). The warming of ocean surfaces fuels hurricanes, intensifying evaporation and transferring heat from the oceans to the atmosphere. As a result, storms and hurricanes have stronger winds, heavier rainfall, and increased surges and flooding. Sea level rise amplifies this threat in coastal areas. Simultaneously, these hurricanes move more slowly, increasing the potential for damage. In 2018, Category 5 Hurricane Michael made landfall in Florida, causing catastrophic loss, with some communities completely destroyed (National Weather Service, 2019). Hurricane Maria, also Category 5, devastated the island of Puerto Rico in 2017 with widespread power outages, flooding, and landslides. The death toll was estimated at almost 3,000,000 (NOAA, 2017).

The frequency of heat waves has steadily risen, from an average of two per year in the 1960s to six per year in the 2020s, with the waves becoming more intense and lasting longer (EPA, 2023f). In July 2023, Phoenix, Arizona, endured a record of 31 days over 110 degrees (The Associated Press, 2023a). Extreme heat jeopardizes human health and labor efficiency in sectors with outdoor work such as agriculture and construction. Heat waves also impact environmental health, affecting animal and plant life and water availability and creating diminished capacity to support agricultural crops.

Extreme heat events are not limited to land. Marine heat waves (MHW), prolonged episodes of intense warming in seas and oceans, are becoming increasingly common and more severe. MHWs are closely monitored as they intensify extreme weather, expedite polar ice melting, and affect the health of marine life. As noted earlier, Earth’s oceans play a pivotal role in storing excess heat, absorbing approximately 90 percent of the planet’s retained heat from greenhouse gases emitted since 1970 (National Aeronautics and Space Administration, 2023). MHWs can have significant consequences for marine ecosystems and fishing industries; higher temperatures stimulate the proliferation of harmful algal blooms, which are toxic to humans, birds, aquatic life, shellfish, and marine mammals and disrupt the migratory routes of marine life. In addition to MHWs, the surface of the ocean is warming; global surface temperatures reached and sustained record levels in July 2023, setting the record for the highest monthly increase above average in sea surface temperature (NOAA National Centers for Environmental Information, 2023c). On July 25, 2023, a heat record was likely broken when the water surface near Miami registered 38.4°C (101.1°Fahrenheit) (Kuta, 2023).

Prolonged elevated temperatures and drought are favorable conditions for the spread of wildfires, and the risks will likely amplify (Figure 14.6) (National Integrated Drought Information System, 2023). The summer of 2023 brought a record wildfire season to Canada; by August 22, even before the end of the season, over 37.8 million acres, more than double the previous record, had burned (Aljabs, 2023). Compare this to the one million acres that burned in the devastating 2018 California wildfires. As climate change progresses, wildfires are becoming more powerful, producing thick walls of smoke that are difficult to penetrate by tanker planes, with heat so intense that water drops can evaporate before reaching the ground. On August 8, 2023, a wildfire rapidly spread across Maui, Hawaii, destroying 2,170 acres including the historic town of Lahaina and thousands of residences and buildings (Hassan & Betts, 2023). The Lahaina fire killed 97 people, making it the fifth deadliest fire in U.S. history (Western Fire Chiefs Association, 2023).

Figure 14.6 Wildfire devastated the community of Lahaina in Maui, Hawaii, during August 2023. (credit: “Maui community of Lahaina burned by wildfire” by State Farm/Flickr, CC BY 2.0

Infectious Diseases

Alterations in the climate impact the prevalence, distribution, and transmission of diseases and the spread of infectious diseases. This relationship underscores the complex interaction between the environment, vectors, pathogens, and human health. Climate change can alter the distribution, seasonality, abundance, and life cycles of vectors that carry diseases such as Lyme, West Nile, Rocky Mountain spotted fever, malaria, plague, chikungunya, dengue, and Zika. Rising temperatures and heavier precipitation create favorable conditions for vectors, enabling them to spread and thrive in previously unaffected regions. Warmer temperatures expedite pathogen development within vectors, shortening their incubation periods and potentially escalating outbreaks. Higher water temperatures, shifting water salinity, and algal blooms cause waterborne diseases from Vibrio species such as cholera to become more prevalent. Modeling of Vibrio along with sea surface temperatures indicates a 51–108 percent increase in cholera cases in the United States by the year 2090 (relative to 1995) (Sheahan et al., 2022). The number of days conducive to Vibrio transmission has more than doubled from 53 to 107 (Aizenman, 2019).

Food System

Climate change threatens the production, quality, stability, supply chains, pricing, and distribution of food. Global agricultural productivity has slowed over the past 50 years due to climate change. Shifts in rainfall amounts, intensified weather events, and increased heat predictably drive down crop yields. For example, compared to 1981, the 2021 growing season for corn was shorter by an average of 9.3 days and for rice, 1.7 days (Romanello et al., 2022). As farmers struggle to adapt to changing conditions, they utilize more herbicides and pesticides, driving up the costs both of fertilizers and of the final food product. Furthermore, elevated atmospheric CO₂ levels reduce the concentration of nitrogen in plants, resulting in lower protein content in crops such as barley and soy. Ocean warming and acidification have adversely affected shellfish and fisheries in some regions, threatening the marine food supply. Rising sea levels and water intrusion increase soil salinity, damaging crops and increasing dietary salt. Extreme weather events such as droughts and heat waves have left millions vulnerable to food insecurity, especially in Africa and Asia, with an estimated 720 million to 811 million people suffering from hunger globally (Romanello et al., 2022). The supply of land and marine animals is also expected to continue declining, further reducing food output and escalating food prices. These factors tend to trigger food insecurity and steer consumers away from nutritious food to more calorically dense but nutrient-poor food, leading to outcomes ranging from nutrient deficiencies to obesity.

Impact on Physical Health

In 2021, the editors of more than 200 medical journals published a statement urging world leaders to rapidly reduce greenhouse gas emissions to avoid irreversible catastrophic harm, referring to climate change as the “greatest threat” to public health (Atwoli et al., 2021). The authors note that the evidence is unquestionable that continued increases in temperature may lead to unstoppable environmental change and global instability.

Climate change and related extreme events will significantly amplify health issues and premature deaths around the world. Increasingly frequent and intensifying extreme events will adversely impact population health by affecting air, water, and food availability, quality, and safety; exacerbating existing medical conditions; straining critical public health infrastructure and health care systems; and disrupting food chains and supply.

Health consequences include both the exacerbation of existing health issues such as respiratory and cardiovascular diseases and new challenges such as emerging zoonoses and water- and foodborne illnesses (Figure 14.7). Furthermore, the climate crisis may multiply threats, creating an acute situation for treatable conditions. For example, a power outage caused by an extreme weather event may lead a stable client with COPD to have an exacerbation.

Figure 14.7 Climate change has a negative impact on health. (See CDC, 2022b; attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Heat-related mortality among those over the age of 65 has increased by more than 50 percent over the last 20 years (Atwoli et al., 2021). Data reveals a clear connection between hot days and higher instances of heat-related illnesses like cardiovascular and respiratory issues (U.S. Global Change Research Program, 2018), renal failure, electrolyte imbalances, kidney problems, fetal health complications, and preterm births. In Phoenix, hospitalizations doubled for heat-related illnesses as well as injury, including burns sustained when falling onto pavement reaching a scorching 180 degrees.

Simultaneously, climate change worsens air pollution by elevating ground-level ozone and particulate matter, leading to worsened respiratory health, particularly for those with asthma and other respiratory diseases. Air quality is also impacted by wildfires; smoke is extremely hazardous to human health as it contains particulate matter, carbon monoxide, nitrogen oxides, and volatile organic compounds. Exposure to wildfire smoke leads to increased cases of respiratory and cardiovascular hospitalizations, emergency department visits, and chronic obstructive pulmonary disease. Communities thousands of miles from wildfires can experience unhealthy air quality from wildfire smoke, as notably occurred during the summer of 2023 when wildfire smoke from Canada spread deep into the United States, resulting in a 17 percent nationwide increase in visits to emergency rooms for asthma symptoms and a 46 percent increase in New York and New Jersey, jumping to 82 percent in New York State on the worst day of air quality, June 7 (The Associated Press, 2023b).

Diseases linked to food, water, animals, and insects, such as malaria, are projected to surge. Food supplies are shifting, with a decline in marine life and diminished agricultural output contributing to worldwide hunger. Even the food we eat is at risk for becoming less healthy, potentially leading to nutrient deficiencies.

Impact on Mental Health

Climate change has profound effects on mental health and psychological well-being. Temperature spikes, heat waves, and high humidity are linked to a decline in mental health outcomes and increased homicide and suicide rates (Romanello et al., 2022). Exposures to climate-related events can lead to a spectrum of mental health consequences, from minor stress to clinical disorders like anxiety, depression, post-traumatic stress, and even suicidal ideation. More indirectly, events like droughts disrupt agriculture, livelihoods, and resource availability.

Extreme weather events can lead to the loss of property, community, and life. Flooding or the threat of floods can trigger heightened levels of depression and anxiety, with these effects persisting for multiple years. Disasters disproportionately affect children, leading to mental health disorders due to forced displacement or the loss of family and community stability. After disasters and droughts, increased use of alcohol and tobacco becomes common. Climate change can intensify conflict and violence, further impacting mental health.

Individuals and communities may face multiple climate change effects. Exposure to multiple climate events can compound and accumulate over time, depleting both resilience and health (EPA, 2023k). Climate change amplifies existing health burdens; communities with degraded ecosystems and weak or outdated infrastructure face higher health risks. Vulnerable groups, including Indigenous communities, older adults, women, BIPOC populations, and individuals who identify as LGBTQIA+, disproportionately bear the consequences of climate change and are particularly susceptible to adverse mental health outcomes. Young people face heightened anxiety and depression and increased substance use. The impact of the climate crisis generated new concepts like climate anxiety (anxiety associated with climate change and its effects), solastalgia (nostalgia for ways of life lost due to climate change), climate despair (a sense of hopelessness and resignation regarding climate change), and ecological grief (an emotional response to the loss of parts of the ecosystem due to climate change) (Ostrander, 2022).

Impact on Vulnerable Populations

Globally, vulnerable populations bear a greater burden due to numerous potential factors such as insufficient community resources, suboptimal health care, and compromised infrastructure, including transportation, water, sanitation, and energy. Vulnerability to climate change depends on exposure to climate stressors, sensitivity to potential harm from the stressors, and adaptive capacity, or the ability to adjust, cope, and respond. Poverty heightens exposure and sensitivity, making those experiencing poverty more susceptible to harm while subsequently limiting adaptive capacity (U.S. Global Change Research Program, 2016).

Groups that experience more exposure to stressors may include those who are of lower socioeconomic status and unable to afford air conditioning or protective equipment such as masks, occupational groups such as outdoor workers who are exposed to extreme heat and insect-borne diseases, and those living in locations more prone to extreme climate change threats, such as droughts or hurricanes. Sensitivity is found among those who have preexisting health conditions such as asthma, pregnant people, and children, who are more sensitive to respiratory hazards. Adaptive ability may be limited in older adults, people with disabilities, and Indigenous peoples who rely on traditional ways for their lifestyles.

Mitigation and Adaptation

Efforts to address the impact of climate change can be divided into two categories: mitigation and adaptation. Mitigation, or the reduction of greenhouse gas emissions and pollutants to slow the rate of change, aims to prevent the planet from warming beyond critical thresholds. Mitigation strategies include investing in renewable and clean energy sources, improving energy efficiency, protecting forests and wetlands, supporting sustainable agricultural practices, improving public transportation, and implementing policies to reduce emissions, such as the Paris Agreement, a global treaty adopted in 2015 to restrict the increase in global temperatures to less than 2°C above pre-industrial levels (United Nations, 2015), a target deemed essential to prevent the most serious consequences of climate change. C-Roads, an online virtual simulator, is a great tool to visualize the impact of potential climate change strategies such as the reduction of carbon emissions.

Adaptation, which refers to preparing for the projected impacts of climate change, focuses on minimizing the negative consequences of climate change while enhancing the ability of communities, populations, and systems to cope with its effects. Adaptation strategies include building more resilient infrastructure to withstand extreme weather events, developing early warning systems for extreme events, implementing water management practices to address changing precipitation patterns, and creating plans for managing risks to public health. Adaptation focuses on minimizing negative consequences of climate change and enhancing the ability of communities, populations, and systems to cope with its effects. Both approaches are essential to address the multifaceted challenges of a changing climate and to ensure a sustainable future.

Green Infrastructure

Green infrastructure uses natural and seminatural elements to create sustainable spaces, especially in urban areas (Figure 14.8). Unlike traditional “gray” infrastructure of concrete and steel, green infrastructure utilizes nature, adding features like parks, community gardens, green roofs, rain gardens, permeable pavement, wetlands, and urban forests. There are several advantages to green infrastructure, including stormwater management, enhanced water and air quality, biodiversity preservation, temperature regulation, and the reduction of greenhouse gas emissions. Green spaces also counter the urban heat island effect, where cities become hotter due to human activity and surfaces absorbing heat. In addition to environmental benefits, green infrastructure boosts community health and cohesion, encouraging physical activity and social interaction. Mental health benefits include better sleep quality, increased social interaction, and exposure to nature.

Figure 14.8 Singapore's Supertrees mimic the function of natural trees, providing a vertical garden home, harnessing solar energy, and even collecting rainwater. (credit: “Supertrees” by Ray in Manila/Flickr, CC BY 2.0)

Climate Justice

Climate justice, an outgrowth of the environmental justice movement, focuses on addressing the unequal and disproportionate consequences arising from climate change. Vulnerable groups experience stark disparities on the impact of climate change, with older adults, children, economically disadvantaged communities, BIPOC individuals, and those with underlying health conditions carry a disproportionate burden. Living in communities that are more hazard prone, already polluted, or reliant on aging infrastructure increases the burden (Atwoli et al., 2021). For example, Indigenous populations in the United States face numerous health threats due to climate change. In Hawai’i and the Pacific Islands, saltwater contamination affects the water supply as sea levels rise. For those living in Alaska, thawing permafrost releases stored organic matter as well as hazardous agents once trapped in the frozen soil, destabilizing infrastructure and potentially contaminating water. Black, Hispanic, and Latino people comprise the majority of the outdoor workforce and are more likely to be impacted by air quality, extreme heat, and high humidity (EPA, 2021a). Older adults are a population of significant concern as their vulnerabilities are amplified by preexisting conditions, limited economic resources, and diminished social networks. The intersection of these multiple vulnerabilities further increases the susceptibility of older adults to climate-related impacts. The risk of injury and death during extreme weather events is pronounced among older adults as they may fear for their safety, experience heat-related illnesses during power outages, experience disruptions to medical care, and have limited transportation options (EPA, 2022b).

Evaluating and addressing vulnerability must encompass an understanding of how these at-risk populations encounter disproportionate, multifaceted, and intricate health risks in response to the changing climate. Furthermore, all strategies, policies, and interventions to address climate change must put climate justice front and center to achieve environmental health equity.