In 2019, an international multidisciplinary Lancet collaboration concluded that climate change poses unacceptable threats to the health of current and future populations worldwide. 1 Extreme weather events, rising temperatures, flooding, droughts, air pollution, and wildfires are steadily increasing around the world. 2 Climate change is among the greatest public health threats of the 21st century and a defining modifier of the global burden of disease. 1 The World Health Organization (WHO) projects there will be approximately 250,000 deaths annually from climate change worldwide between 2030 and 2050 3. The direct effects of climate change are both obvious and insidious, leading to acute and chronic diseases that result from increased temperatures, food and water insecurity, air pollution, and vector-borne diseases. The poor and disenfranchised are affected disproportionately by climate change, with conflict and mass migration stemming from hostile environmental conditions.
The Problem: How Climate Change Affects Human Health
The largest geophysical global climate change is the steady rise in temperatures worldwide. 4 Global temperature rise is driven primarily by combustion of fossil fuels and deposition of greenhouse gases in the atmosphere at a rate that exceeds natural processes. Without immediate mitigation efforts by major industrialized nations, the morbidity from rising temperatures will be difficult to prevent. Even small changes in temperature and precipitation result in large changes in disease transmission and serious chronic illnesses. 5 Children, low-income families, individuals with preexisting conditions, pregnant women, and the elderly are the most susceptible to the health effects of increased heat. Pregnant women are particularly vulnerable to ambient heat, as rising temperatures may have a direct effect on human gestational time, increasing the risk of premature birth and birth defects. 6 Importantly, the number of people exposed to annual heat waves is growing: Globally in 2018, 220 million people experienced heat waves, far above previous records. 7
Related to temperature increases are extremes of precipitation and the intensity of storms. Rising temperatures contribute to the spread of vector-borne 8,9 and water-borne10 diseases and lead to the growth of fungi and molds that increase respiratory and asthma-related illnesses. 11 While rainfall increases dramatically in some regions of the world, long-term droughts occur elsewhere. Droughts can increase the risk of vector-borne diseases spread by container-breeding mosquitoes in communities without safe, reliable access to water. 12 Droughts reduce yields and nutritive value of crops, contributing to food insecurity, malnutrition, starvation, and mass migration. 13
Climate change is also inextricably linked to ambient air pollution, a leading global risk factor for premature death. For instance, warming temperatures exacerbate production of key pollutants such as ozone, and climate-driven increases in fuel aridity have driven large increases in wildfires across the United States and around the world, undoing decades of air pollution improvements. 1 Proposed climate change mitigation policies—particularly policies intended to transition us toward cleaner energy sources in electricity production and transportation—would likely have large air quality benefits. Resulting changes in air quality would substantially affect a range of health outcomes. Breathing polluted air damages the heart, lungs, and other vital organs, contributing to premature deaths. 1,14 Exposure to ambient air pollution, most notably fine particulate matter < 2.5 μm (PM2.5), leads to diseases such as stroke, heart disease, lung cancer, asthma, chronic obstructive pulmonary disease, and respiratory infections. 15–18 The WHO estimates that 7 million people die annually from exposure to air pollution, making it the largest global environmental risk factor for premature mortality. 19 An estimated 4.2 million pediatric deaths around the world are linked to ambient air pollution, and more than 90% of the world’s children are exposed to high levels of PM2.5. Air pollution and heat have also been linked to low birth weight, preterm birth, infant mortality, congenital cataracts, neural tube defects, and increased birth rates on days hotter than 90°F. 20–23
In 2017, approximately 22 million people around the world were forced to leave their homes because of “sudden onset” weather events such as flooding, forest fires, droughts, and intensified storms. The Brookings Institution 24 projects that populations in Latin America, sub-Saharan Africa, and Southeast Asia will generate 143 million more climate migrants by 2050 than they did in 2019. Climate change is also contributing to slower-onset environmental shifts that can force human migration, such as desertification, sea-level rise, ocean acidification, air pollution, rain pattern shifts, and loss of biodiversity. Enlarging refugee camps have high rates of diarrheal diseases, measles, acute respiratory infections, malaria and other vector-borne diseases, sexually transmitted infections, malnutrition, and chronic disease complications. 25
Climate change also increases mental health disorders due to weather disasters, forced migration, food insecurity, and extreme heat waves. Posttraumatic stress disorder, depression, domestic abuse, general anxiety, and substance abuse have all been associated with climate change in some contexts. 26 In the United States, the numbers of deaths and emergency department visits for mental health emergencies have been associated with periods of high ambient temperatures, 27 as have the rates of suicides and domestic violence. 26,28
Finally, it is important to recognize that hospitals and laboratories emit 4.4% of the world’s greenhouse gases and are responsible for more than 5 million tons of waste each year. 29 Medical schools and trainees help lead the effort to reduce this pollution. Many institutions have launched environmental initiatives, from energy conservation to green lab programs. In December 2018, 7 Boston-area teaching hospitals and clinical institutes, including Harvard Medical School, announced a commitment to decarbonize. The University of California system has pledged to become 100% reliant on clean electricity for its campuses and medical centers by 2025, and the Cleveland Clinic is working to become carbon neutral by 2027. Numerous hospitals, including the Columbia University Medical Center and Shands Cancer Hospital at the University of Florida, have received LEED certifications. 30
The Training Gap: Climate Change and Medical Education
Given the potential burden of diseases related to climate change, medical trainees must learn to recognize, treat, and prevent climate-related health conditions in their patients. The global pandemic of COVID-19 has starkly demonstrated that society and physicians must be ready to deal with sudden health-related events. Though more insidious in general, climate change already produces extreme weather events that need prepared health care systems. Physicians should be trained to work on mitigation, adaptation, and policy making around climate change. Studies show, however, that most students and physicians in practice lack the necessary knowledge and skills to do so. 31–33 Despite this training gap, climate change is not an educational priority at most U.S. medical schools. In 2018, an Association of American Medical Colleges survey of 147 medical schools found that only one-third included any climate education in their curricula. 34 The WHO, the American Medical Association (AMA), and the National Academy of Sciences each have published calls for physicians and physicians-in-training to develop a basic knowledge of the science of climate change and an awareness of the associated health risks. The AMA, at its June 2019 meeting, pledged the organization to promote education for medical students and physicians on the health threats from climate change. 35 It specifies that curricula should prepare medical students, residents, and clinicians to have “a basic knowledge of the science of climate change, can describe the risks that climate change poses to human health, and to counsel patients on how to protect themselves from the health risks posed by climate change.” 36 Despite these calls for new curricula, most U.S. medical schools still offer little to no education on the health impacts of climate change. 37
The most compelling demands for climate change education come from medical students themselves, as they anticipate the uncertainties of future practice in a rapidly changing world. To this end, students organized a national alliance, Medical Students for a Sustainable Future (MS4SF.org), to address the need for climate education in U.S. medical schools. Similarly, medical students in Australia and Germany are pursuing related curricular reform. 38,39 At Stanford University School of Medicine, medical students (A.G., J.G.) requested, codesigned, and helped to implement a new elective course in 2020, entitled The Impact of Climate Change on Human Health. The course examines the intersection of climate change and population health, pediatrics, women’s health, psychiatry, infectious disease, and disaster management, along with advocacy and the greening of health care. Students from across the university have enrolled in the course.
Like Stanford, those U.S. medical schools that offer climate education generally do so through elective and seminar courses. As the momentum and successes of these courses increase, so will the demand for a more comprehensive approach to training, with climate science integrated into pertinent preclinical and clinical experiences. 40 We anticipate increased demand for climate education across the continuum of medical training, including postgraduate and continuing medical education activities. 40
Several U.S. medical schools are early adopters of climate science education in their preclinical curriculum (Table 1). The University of Minnesota Medical School in Minneapolis, the Carle Illinois College of Medicine at the University of Illinois at Urbana-Champaign, and the Icahn School of Medicine at Mount Sinai recently added some climate change-related content to their curricula. At Icahn, for example, first-year students are offered an elective, 1-week seminar course on climate change as part of a global health module. 41 Georgetown University School of Medicine provides a series of educational modules for medical students to explore the connections between air pollution and climate change, allowing them to identify sources of lung irritants, examine air quality data throughout the world, and offer patient care recommendations for relevant conditions. One of the most comprehensive programs is at the University of California, San Francisco, School of Medicine (UCSF), where first- and second-year medical students receive core lectures on climate and health and have the option to do a deeper dive through an inquiry immersion course. UCSF students are also exposed to climate change education through the UCSF Program for Reproductive Health and the Environment, and they can take a 10-week elective similar to the course at Stanford. Arianne Teherani, a research faculty member in the Office of Research and Development in Medical Education at UCSF, is currently developing a comprehensive curriculum for educating students on environmental sustainability and health and is bringing together faculty and staff to form an interdisciplinary community of environmental sustainability and health educators at UCSF. 40,42
Longitudinal, integrated climate change curricula are also under consideration by several institutions. 34,38,40,43,44 Students and residents should be taught how climate change affects different medical specialties, ranging from disease and organ systems to disaster preparedness and supply shortages. UCSF and Georgetown are planning to implement an interesting addition to clerkship education: Students rotating through clinics/offices would undertake projects to improve sustainability practices in health care and educate patients about climate change. Additionally, the Department of Emergency Medicine at the University of Colorado Anschutz Medical Campus sponsors a successful 2-year fellowship, Climate and Health Science Policy for physicians. 29 For physicians already in practice, Yale University School of Medicine offers a continuing education certificate related to climate change.
A Call to Action for Medical Schools
The Earth’s climate is changing rapidly, and the manifestations of these changes are likely to intensify. We can no longer ignore the direct and indirect effects of these changes on human health. The next generation of physicians must be better prepared to address the many implications of climate change on the mental and physical health of their patients and society. Physicians can play a crucial role in climate change mitigation and health system adaptation to prepare for emerging health threats. Despite compelling climate science, the greatest pressure for curricular change comes from medical students who fear graduating with little or no knowledge in this domain. Medical schools are responding to student demands, but slowly. The slow response to threats of climate change by the international community should not be mirrored in medical education. We believe there is an urgent need for broad, multidisciplinary climate science education for physicians, ideally integrated within each pertinent course or program of study, across the continuum of medical training. Efforts invested in physician training now will benefit their communities—generations of patients—whose health will be impacted by a period of remarkable climate change.
The authors would like to thank Dr. Christopher Dant for his helpful editorial support, Dr. Michele Barry for support of ideas in the review, as well as the Stanford Woods Institute, Lane Center for the West, the Sean N. Parker Center for Allergy and Asthma Research at Stanford University, and Stanford Global Health.
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