Changing Earth and Climate Change
Planetary Boundaries
Over the past 65 years, human health and well-being have improved dramatically. Compared to 1950, the global population in 2015 more than tripled, while the proportion of people living in extreme poverty decreased from 63% to 10%. The average life expectancy increased from 46 years to 72.3 years, and the under-five mortality rate dropped from 225 per 1,000 live births to 45 per 1,000 [1]. However, other living organisms on Earth are facing worse conditions than ever before in history. Approximately one million species are at risk of extinction, with many predicted to disappear within the next few decades. Since 1970, the global populations of birds, mammals, reptiles, amphibians, and fish have already declined by more than 50% [2]. Currently, the global human population of 8 billion has deforested approximately half of the world’s temperate and tropical forests, dammed over 60% of rivers, and converted 40% of the Earth's surface into farmland and pasture. Additionally, massive extraction and consumption of natural resources have led to significant environmental changes, including climate change [2]. This phenomenon is referred to as the ‘Anthropocene Acceleration’ [3].
Scientists from the Stockholm Resilience Center first introduced the concept of ‘Planetary Boundaries’ in 2009 and revisited it twice in 2015 and 2023 [4]. Planetary boundaries indicate critical thresholds in Earth’s environmental system that, if crossed, could lead to abrupt or irreversible large-scale environmental changes, increasing the risk to ecosystems upon which humanity depends. Nine planetary boundaries have been identified to ensure sustainable development and human prosperity. These include climate change, biosphere integrity, stratospheric ozone depletion, ocean acidification, biogeochemical flows (phosphorus and nitrogen cycles), land system change, freshwater use, atmospheric aerosol loading, and the introduction of novel entities. Among these, climate change and biosphere integrity are considered the most critical components of the Earth system. According to a 2023 study, humanity has already crossed six out of the nine planetary boundaries (Figure 1)[5]. The interactions among these boundaries indicate that focusing solely on climate change is insufficient for ensuring sustainability. Instead, an integrated approach considering the interactions between climate change and biodiversity loss is necessary.
These unprecedented environmental changes significantly impact human health. Paradoxically, breaching six of nine planetary boundaries shows human progress now threatens survival and health. The concept of ‘Planetary Health’ has been proposed, emphasizing that preserving biodiversity and nature is essential for safeguarding human health [6]. The crisis of the Earth's environment is primarily driven by rapid population growth, a sharp rise in per capita consumption, and technological innovations that have substantial environmental impacts. In turn, it impacts human societies through various pathways, leading to issues such as malnutrition, exposure to infectious diseases, non-communicable diseases, migration, conflict, and mental health risks, etc.
Greenhouse Gases and Climate Change
Climate change refers to statistically significant variations in climate patterns over extended periods, typically decades or longer. The causes of climate change include natural factors such as solar cycles, sunspot activity, changes in Earth's orbit and axial tilt, and large-scale volcanic activity, as well as anthropogenic factors resulting from human activities. The rapid climate changes observed over the past 200 years are primarily attributed to human activities, particularly since the Industrial Revolution, which led to a dramatic increase in greenhouse gas (GHG) emissions [7]. More than 91% of the excess solar radiation trapped by GHGs is absorbed by the oceans, causing rising sea temperatures. Meanwhile, 5% contributes to land warming, 4% to glacier loss, and 1% to atmospheric warming. Recognizing these effects, the World Meteorological Organization (WMO) identifies four key indicators of climate change: GHG concentrations, ocean temperatures, ocean acidification, and sea level rise [8].
The Kyoto Protocol (1997) identified six major GHG: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF6). Later, nitrogen trifluoride (NF3) was added in the 18th Conference of the Parties (COP18, 2012) (Table 1). The Global Warming Potential (GWP) index measures the relative effectiveness of each GHG in trapping heat in the atmosphere compared to CO2 over a 100-year period. This index is based on radiative forcing (the amount of heat energy absorbed in the atmosphere) and atmospheric lifetime [9]. Since GHG persist in the atmosphere for long periods and spread globally without regard to national borders, GHG emitted by developed countries impact developing nations, and past emissions affect future generations.
The consequences of global warming include melting polar ice caps, rising sea levels, submergence of coastal and island regions, and increased frequency of extreme weather events such as heatwaves, heavy snowfall, floods, storms, and wildfires. These events are expected to intensify in the future (Table 2) [10].
According to the Intergovernmental Panel on Climate Change (IPCC), if global temperatures increase by more than 1.5°C compared to pre-industrial levels (before 1900), the risks posed to ecosystems and humanity could become unmanageable. Recent IPCC reports suggest that climate risks are more severe and long-term than previously anticipated.
Climate Risk Inequality
The top 10% of income earners hold 76% of the world’s total wealth, while the bottom 50% possess only 2%, and this disparity continues to widen. In 2019, the top 10% and the bottom 50% income groups contributed 48% and 12% of global carbon emissions, respectively, but the bottom 50% suffered 75% of the income losses caused by climate change (Figure 2)[11].
According to climate models, temperature variability in tropical countries, including the Amazon, is expected to increase continuously over the next few decades. Due to soil drying and changes in atmospheric structure, the temperature variability per 1°C of global warming increases by up to 15% in the Amazon and southern Africa during seasons with maximum solar radiation. In contrast, outside the tropics, temperature variability is predicted to decrease on average due to the reduction in meridional temperature gradients and sea ice loss. This means that the countries that have contributed the least to climate change but are the most vulnerable to climate variability will experience the greatest temperature fluctuations and the most extreme weather conditions [12]. Currently, 1.81 billion people, or 23% of the global population, are directly exposed to once-in-a-century floods, and among them, 89% reside in low- and middle-income countries. Of the 170 million people facing both extreme poverty (living on less than $1.90 per day) and flood risks, 44% live in sub-Saharan Africa. Poverty diminishes the ability to adapt to and respond to natural disasters, making regions affected by both poverty and flood risks the most vulnerable [13].
Global warming caused by climate change also affects gross domestic product (GDP), following an inverted U-shape relationship. The highest GDP levels are found in regions where the annual average temperature is around 13°C. Most developed countries in the northern hemisphere fall within or below this temperature range, whereas many developing nations near the equator have higher average temperatures. As a result, global warming has reduced the GDP growth potential of equatorial countries by over 25%, whereas northern hemisphere countries have seen more than a 20% increase. By projecting these trends into 2100, global warming is expected to increase GDP in the northern hemisphere while significantly decreasing GDP in equatorial and southern hemisphere countries, exacerbating global economic inequality [14]. Unequal climate change risks are also evident in agricultural productivity. Since 1961, climate change has reduced global agricultural productivity by approximately 21%, with hotter regions such as Africa, Latin America, and the Caribbean experiencing even more severe losses, ranging from 26% to 34% [15].
Climate damage disproportionately exacerbates socioeconomic inequality, creating a vicious cycle [16]. Socioeconomically disadvantaged groups lack private resources to respond effectively to climate disasters, and they often have limited political influence, reducing their access to public resources. As a result, these communities face greater climate risks, experience more severe damage, and have lower capacity to recover from disasters, intensifying existing socioeconomic inequalities (Figure 3).
In fact, the most vulnerable communities suffer the most from the health effects of climate change, are the least prepared for transitioning away from fossil fuels, and experience the greatest exposure to energy poverty and air pollution caused by fossil fuels [17]. In response, at COP28 (2023), UNFCCC member states agreed to establish a 'Loss and Damage Fund' to support developing countries experiencing irreversible damage due to climate change. This initiative also includes biennial dialogues on a Just Transition Work Program to ensure equitable climate adaptation efforts [18].
Climate Change’s Impact on Health
Pathways of Climate Change’s Impact on Health
Climate change affects health both directly and indirectly [19]. Direct impacts include damage and fatalities caused by extreme weather events such as floods, storms, droughts, and heatwaves. Indirectly, climate change affects health through disruptions to natural ecosystems, socio-economic shocks, reduced agricultural productivity, and changes in food and water availability and pricing. Disasters such as floods and droughts displace large populations, increasing malnutrition, infectious diseases, and mental stress (Figure 4).
In general, the relationship between mortality rates and temperature follows a J-shaped curve, where mortality rates increase significantly when temperatures rise above or fall below a critical threshold for a specific region. In colder regions, as temperatures rise due to climate change, the incidence of extreme cold weather decreases, thereby reducing mortality risks. However, in warmer regions, mortality rates are expected to rise significantly. These effects predominantly affect people aged 64 and older, and wealthier populations tend to have greater adaptability through air conditioning and other technologies, whereas low-income populations experience disproportionate excess mortality from heat-related conditions. By 2100, excess mortality per 100,000 people is projected to increase by 140 in Ghana but decrease by 150 in Germany [20].
Changes in extreme weather patterns, temperature, and precipitation affect agricultural productivity, causing crop damage and destruction. Increased CO2 levels in the atmosphere also reduce the protein content of crops, lowering food quality [21]. As a result, malnutrition and food insecurity are worsening, especially in sub-Saharan Africa and South Asia. In particular, preventable deaths among children under the age of five is expected to increase in low- and middle-income countries [22]. Consequently, climate change disproportionately affects vulnerable populations, including low-income countries in the Global South, children, women, people with disabilities, indigenous communities, and the elderly.
Connection Between Climate Change, Biodiversity, and Infectious Diseases
The Convention on Biological Diversity (CBD) defines biodiversity as the variability among living organisms, including terrestrial, marine, and aquatic ecosystems, and the ecological complexes of which they are part. Biodiversity includes genetic diversity, species diversity, and habitat diversity, all of which contribute to ecosystem stability and human well-being.
Species can adapt to climate change by migrating, altering seasonal behaviors, exhibiting physiological flexibility, acclimating, or undergoing evolutionary adaptations [23]. However, rapid climate change and extreme weather vents outpace many species’ ability to adapt, leading to regional extinctions and ecosystem disruptions [24]. Warming alters physiological characteristics and seasonal cycles [25], weakens food web resilience [26], and increases species extinction risks.
Currently, biodiversity loss is occurring at an unprecedented rate in Earth’s history. According to the Living Planet Index (LPI), which tracks vertebrate populations (mammals, birds, amphibians, reptiles, and fish), wildlife populations declined by an average of 73% between 1970 and 2020 [27]. The Red List of Threatened Species reports that by 2024, over 46,300 species worldwide are at risk of extinction [28].
Biodiversity-rich forests and grasslands have high carbon sequestration capacity, mitigating climate change [29]. However, deforested land converted for agriculture or urban development exacerbates GHG emissions [30]. Urban heat islands experience higher temperatures due to reduced vegetation. The loss of keystone species decreases primary production and carbon sequestration, while reduced predator diversity weakens ecosystem balance and accelerates climate change [31].
Biodiversity changes are closely linked to the emergence and spread of infectious diseases. Higher biodiversity reduces pathogen transmission by limiting pathogen-host interactions (dilution effect). Conversely, biodiversity loss increases pathogen reservoirs and amplifies disease spread (amplification effect) [32,33]. Various ecological factors influence this process [34], including changes in reservoir hosts and vector species (e.g., range expansion, population growth, habitat shifts), which significantly affect disease outbreaks [35].
Over 60% of emerging infectious diseases originate from animals, with 72% linked to wildlife. The frequency of zoonotic spillovers is increasing, driven by population growth, land development, overexploitation, pollution, climate change, social inequality, global trade, and travel [36,37]. Deforestation and habitat destruction increase human-wildlife interactions, creating ideal conditions for the emergence and spread of new infectious diseases. A meta-analysis of global change drivers and infectious disease emergence found that biodiversity loss, invasive species, climate change, and chemical pollution are associated with higher disease prevalence, whereas urbanization was associated with reduced disease risk [38].
GHG emissions and climate change exacerbate infectious diseases. 58% of infectious diseases worldwide are worsened by climate-related hazards, while only 16% are mitigated. Key climate drivers of infectious disease outbreaks include global warming, precipitation changes, floods, droughts, and storms. For instance, melting permafrost in extreme heat may release unidentified pathogens including viruses originating from ancient organisms and known pathogens such as anthrax spores, while floods increase waterborne diseases such as leptospirosis, typhoid, and cholera. Rising mosquito habitats elevate the risk of dengue fever and malaria [39].
Climate change, biodiversity loss, and infectious diseases are interconnected, often triggering cascading effects [40]. Consequently, the World Health Organization (WHO) recommends addressing climate-related health issues using a One Health approach and Nature-Based Solutions (NbS) [41]. One Health is defined as an integrated approach that aims to sustainably balance and optimize the health of humans, animals, and ecosystems. It recognizes the interconnectedness of human, livestock, wildlife, and ecosystem health, requiring cross-sectoral collaboration to improve public health. According to the International Union for Conservation of Nature, NbS are actions that protect, manage, and restore natural or modified ecosystems to effectively address societal challenges while benefiting human well-being and biodiversity [42]. NbS is particularly important for food safety, zoonotic disease management, and antimicrobial resistance control.
Directions for Climate Response in the Healthcare Sector
Integrated Climate Health Resilience and Emission Reduction in Healthcare
The IPCC, in its Fifth Assessment Report (2014), defines climate vulnerability as one of the three key components of climate risk, along with climate hazards and exposure. These components are influenced by changes in climate systems and socioeconomic processes, evolving over time [43]. The WHO aligns with this framework by linking climate hazards, vulnerability factors, and exposure to the role of health systems in resilience and GHG emission reduction. As shown in Figure 5, changes in health systems and socioeconomic processes (strengthening resilience and reducing GHG emissions) affect hazards, exposure, and vulnerability, ultimately influencing health outcomes and the performance of healthcare systems. Additionally, since health systems contribute to GHG emissions, they must not only enhance resilience but also optimize resource use and reduce emissions to mitigate health risks [44].
To build climate-resilient healthcare systems, it is necessary to assess climate change-related health vulnerabilities and adaptation capabilities, develop national health adaptation plans, and secure funding for climate-related health initiatives. Similarly, to establish sustainable, low-carbon healthcare systems, countries should set bold carbon neutrality targets, develop GHG emissions accounting frameworks, and implement action plans to transition towards low-carbon healthcare. Previously, WHO’s 2015 framework focused primarily on climate health risk preparedness and adaptation. However, in 2023, an updated framework was introduced, integrating GHG emission reduction strategies into the healthcare sector. This revised framework emphasizes synergies between mitigation and adaptation measures in healthcare policy (Table 3).
In 2021, the healthcare sector accounted for 4.6% of global GHG emissions, marking a 9.5% increase from 2020 and a 36% increase from 2016 [17]. In 2014, South Korea’s healthcare sector contributed 5.3% of the nation’s total emissions, ranking 8th globally in total emissions and 5th in per capita emissions [45]. GHG emissions from healthcare facilities are categorized into three scopes: Scope 1 for direct emissions from healthcare facilities, Scope 2 for indirect emissions from purchased electricity and energy, and Scope 3 for indirect emissions from entire supply chains, including production and transportation of medical goods and services, excluding Scope 2. More than 70% of healthcare-related emissions originate from Scope 3, and in South Korea, this proportion is 75%, highlighting the healthcare sector’s influence on decarbonization efforts in other industries.
However, higher life expectancy does not necessarily correlate with higher per capita healthcare emissions [46]. For instance, while the U.S. emits 50 times more per capita than India, it ranks 6th lowest in life expectancy (66.2 years). Among the top 10 countries with the highest life expectancy, South Korea’s healthcare emissions (1,065 kg CO2e) are significantly higher than France’s (321 kg CO2e), demonstrating that high-quality healthcare can be provided with lower emissions (Figure 6).
Maximizing the Health Benefits of GHG Reduction Measures
Efforts to reduce GHG emissions can provide direct health benefits both in the short and long term. These benefits mainly arise from well-designed and effectively implemented measures in the energy, AFOLU (agriculture, forestry, and other land use), and transport sectors, leading to improved air quality, the promotion of sustainable and healthy diets, active travel, and increased use of public transportation [47].
Most sources of GHG emissions also contribute to air pollution. In high Human Development Index (HDI) countries, the gradual phase-out of coal resulted in a 6–9% reduction in outdoor PM2.5-related deaths between 2016 and 2021. However, in 2020, indoor PM2.5 exposure from solid household fuel combustion caused 2–3 million deaths across 65 countries [17]. Since fossil fuel combustion accounts for 68% of global GHG emissions [48], shifting energy structures is crucial for both climate and health benefits. Fossil fuels cause air, soil, and water pollution throughout their entire lifecycle—from extraction, production, and usage to disposal—posing health risks to exposed populations [49]. In 2019, air pollution-related deaths reached 6.7 million, with over 90% occurring in low- and middle-income countries [50]. People living near mining areas or power plants, workers engaged in related industries and processes, and all individuals exposed to pollutants generated by fossil fuel combustion can experience various types of health impacts. Furthermore, coal ash residue from combustion contains radioactive elements, minerals, and heavy metals, which can affect the health of children living near coal ash disposal sites [49] and increase the risk of various diseases among oil spill cleanup workers [51].
The food system accounts for up to 30% of global GHG emissions [52], with global agricultural emissions increasing by 2–9% between 2016 and 2021. Red meat and dairy production contributed 56% of agricultural emissions in 2021, while deaths linked to red meat consumption increased from 14 to 16 per 100,000 people [17]. Excessive consumption of red and processed meats and inadequate intake of high-quality plant-based foods not only contribute to GHG emissions but also increase health risks [53]. A cultured meat, a lab-grown meat, holds significant potential for climate change mitigation, but its current environmental benefits remain uncertain due to high energy demands and limited large-scale implementation [54].
Road transport accounts for approximately 11% of global GHG emissions [48]. The proportion of electric vehicles (EVs) increased by only 0.19% from 2016 to 2021, reaching 17 million by 2024. However, in 2021, fossil fuels accounted for 95.2% of the road transport energy sector, and global transport sector carbon emissions returned to their pre-pandemic peak in 2022 [55]. To rapidly reduce transport-related emissions and prevent socio-economic inequalities stemming from high EV costs, a shift towards public transportation and reduced personal vehicle reliance is essential. Affordable and accessible public transportation systems should enable zero-emission, safe, and active mobility (e.g., walking or cycling), reducing air pollution, transportation inequality, and improving public health [56].
Meanwhile, forests are critical carbon sinks, biodiversity reserves, and sources of food, medicine, and knowledge, i.e., ecosystem services [57]. Numerous scientific studies have demonstrated that greater exposure to greenness is associated with improved mental health, reduced risk of chronic diseases, increased physical activity, and better overall well-being [58]. Deforestation exacerbates climate change while increasing wildfire risks, zoonotic disease transmission, and allergy risks [59]. Between 2001 and 2022, approximately 459.4 million hectares (11.5%) of global forests were lost. Highly developed countries experienced the most significant forest area losses, primarily due to forestry activities (30%), agriculture (27%), wildfires (22%), and logging for raw materials (20%) [17].
Areas for Improvement in Climate Health Response in South Korea
Since 2011, South Korea has been establishing a National Climate Change Adaptation Plan every five years. In 2023, the government introduced the Third Strengthened Adaptation Plan (2023-2025). This revision was necessary because previous plan was based on IPCC AR5, which underestimated the severity of the climate crisis compared to IPCC AR6. Therefore, it is crucial to strengthen adaptation infrastructure across all sectors and implement practical action plans to enhance field-level adaptation [60]. There are two key areas for improvement in the national adaptation measures for health and vulnerable populations in response to climate change.
First, there is a need to expand policy domains and target groups to strengthen climate health resilience. Currently, the health impacts of climate change are primarily focused on infectious diseases, but it is crucial to recognize and address a broader range of health effects, including non-communicable chronic diseases. Additionally, climate-related health impact monitoring and service support measures are mostly limited to the elderly, highlighting the need to expand the scope of adaptation efforts. In particular, there is a significant lack of policies to empower future generations—children and adolescents, who are among the most vulnerable to the climate crisis—to become active participants in climate adaptation. Furthermore, workers are increasingly exposed to hazardous working conditions due to extreme climate variability, and the transition to a decarbonized economy heightens the risk of job displacement. Therefore, it is essential to develop concrete policies that ensure safe adaptation and a just transition for workers.
Second, health and quality of life indicators should be developed and utilized in the evaluation and monitoring of adaptation measures across various societal sectors. While mitigation measures across sectors yield direct health benefits, adaptation policies in areas such as water and sanitation systems, food and agriculture, energy production, healthcare systems, human infrastructure, natural ecosystems, and the economy also have the potential to improve health outcomes [17]. For example, adaptation policies in the water management sector could incorporate indicators related to toxic algal blooms and waterborne pathogens/diseases caused by flood, heavy rainfall or heatwave. Similarly, the agricultural and fisheries sectors could include indicators related to foodborne pathogens/diseases, and nutritional status, considering the impact of climate change on food systems and prices.To achieve these improvements, a collaborative and communicative framework between health sector and key adaptation sectors in society is needed.
The Korea Disease Control and Prevention Agency’s "Mid-to-Long-Term Climate Health Plan (2024-2028)" focuses on strengthening disease surveillance, climate crisis preparedness and response systems, and adaptation infrastructure to enhance climate health resilience [61]. Unlike the integrated approach to mitigation and adaptation proposed by the WHO, however, it does not include GHG reduction strategies or measures for the health sector. The big 5 hospitals were among the top 20 buildings in 2022 Seoul in terms of GHG emissions [62]. While their emissions are on the rise, the UK’s National Health Service (NHS)[63] and Kaiser Permanente, a leading Health Maintenance Organization (HMO) in the U.S. [64], have successfully reduced their GHG emissions through planned carbon neutrality initiatives.
To promote GHG reduction efforts in Korea’s health sector, a system for estimating and monitoring GHG emissions in the sector must first be established. To achieve this, a legal framework should be introduced, including mandatory bottom-up reporting requirements. Additionally, policy measures—both regulatory and non-regulatory—should be considered, such as incorporating GHG reduction efforts and performance into medical institution accreditation standards or providing financial incentives for healthcare facilities that actively reduce their emissions. Expediting the currently uncertain timeline for corporate climate disclosure requirements could also be helpful.Furthermore, efforts to improve energy efficiency and reduce GHG emissions and medical waste are emerging in various clinical procedures [65], including dialysis and kidney disease treatment [66], endoscopy [67], and clinical trials [68]. To improve existing high-emission medical practices and protocols, it is necessary to foster awareness and behavioral changes among healthcare professionals, while simultaneously generating scientific evidence on the safety of improved clinical procedures.
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