Physician action against climate change and global environmental degradation has built slowly over 50 years. As early as 1972, immunologist-turned-human-ecologist Stephen Boyden feared that “trends in the relationship between human society and the total environment constitute a serious threat to the survival of civilization and mankind.” We had brought the problem on ourselves, he noted: the use of fossil fuels had increased to such an extent that “the integrity of the biosphere as a whole is now considered by many ecologists to be in jeopardy.”17 Like his mentor René Dubos, a medical scientist and 1960s counterculture idol, Boyden excelled in linking health and environment on a global scale.18,19 Both Boyden and Dubos engaged in the “planetary thinking” that flourished after World War II, sharing an enthusiasm for systems ecology and cybernetics and becoming immersed in the environmental movement that was stimulated, in part, by Rachel Carson’s 1962 Silent Spring.20 Both expressed concerns about “diseases of civilization,” which they understood as the health and ecologic risks posed by globalized industrial capitalism.21

Another crisis emerged in parallel. The advent of nuclear weapons gave humans the power to destroy and corrupt airs, waters, and places in ways newly threatening to life on the planet. In Boston, health professionals recognized the need to act and founded Physicians for Social Responsibility (PSR) in 1961. The following year, they published articles in the Journal about the medical consequences of nuclear war.22,23 These generated substantial attention from the local and international press and government officials and became a model for other antinuclear movements. Collaboration with Soviet scientists led in 1980 to the establishment of International Physicians for the Prevention of Nuclear War (IPPNW). Both PSR and IPPNW articulated an ethic that extended physicians’ responsibility beyond the clinic and into national and global politics. IPPNW’s 1985 Nobel Prize validated this mode of physician advocacy.

Climate change gained new urgency in the late 1980s, as pessimistic reports appeared with sobering frequency. In 1987, the World Commission on Environment and Development, chaired by physician Gro Harlem Brundtland, alerted epidemiologists and others to the ways in which our abuse of Earth’s ecosystems threatened human health.24 The Intergovernmental Panel on Climate Change, established in 1988 by the World Meteorological Organization and the United Nations Environment Program, issued its first assessment in 1990.25 The World Health Organization soon offered its own reports on the health effects of environmental change.26 In 1992, the United Nations Conference on Environment and Development, or “Earth Summit,” produced the Framework Convention on Climate Change (further developed in Kyoto and Paris), which helped to structure international responses to climate change.27 That same year, the Union of Concerned Scientists delivered a stark “Warning to Humanity,” pointing out that a “great change in our stewardship of the earth and the life on it is required if vast human misery is to be avoided and our global home on this planet is not to be irretrievably mutilated.”28

Accumulating evidence of an anthropogenic climate emergency incited more physicians to take action. “The subject of climatic and environmental changes that result from human activity has been much in the news recently,” physician Alexander Leaf wrote in the Journal in 1989, “but the impact of environmental change on the health and survival of humans has received relatively little direct attention.” Leaf, who had been active in both PSR and IPPNW, drew parallels between climate change and nuclear war: “Physicians and other scientists have served an important function by educating themselves, the public, and political leaders to the dangers of a nuclear war. We may have a similar function in publicizing the potential effects of global atmospheric changes.”29 Education could bring about political reform: “Only an educated and aroused public is likely to force antiquated nationalistic political systems to cooperate.” Several physicians heeded this call and published further warnings about climate change in leading medical journals.30,31 PSR created a health and environment branch in 1992 and, after a lively conference at the Massachusetts Institute of Technology, issued a stark report the following year: Critical Condition: Human Health and the Environment.32 Harvard Medical School established its Center for Health and the Global Environment in 1996. But even though Leaf had tapped into a widely felt anxiety and broadcast his concerns in a prominent venue, and despite the interest within PSR, these efforts initially gained little traction beyond a small circle of like-minded advocates.

Proponents of the cause, however, persevered. Several radical epidemiologists, committed to environmental health, took up the climate challenge in the 1990s. “In the longer-term (and admittedly anthropocentric) view of macroenvironmental degradation,” observed Australian epidemiologist A.J. McMichael in 1991, “the ‘bottom line’ will be dominated by adverse effects upon human health and survival.”33 A reader of Dubos and Boyden, McMichael established programs on the health consequences of climate change at the London School of Hygiene and Tropical Medicine and the Australian National University. For the first time, one of Earth’s species threatened global ecosystems on which its own health depended; Boyden’s warnings seemed on the verge of realization. “The regenerative and absorptive capacity of the biosphere has its limits,” McMichael warned. “Thresholds, once exceeded, may trigger unexpected events as, for the first time, we push global ecosystems beyond their usually resilient limits.”34 McMichael and colleague Andy Haines worked for decades to alert health professionals to the danger of overloading the earth’s natural systems.35,36

Such advocacy eventually elicited broader institutional responses. In 2014, with funding from the Rockefeller Foundation, Lancet editor Richard Horton convened a Commission on Planetary Health.37 Chaired by Andy Haines, the commission issued its report on the enfeebled condition of the earth’s natural systems the next year, giving currency to the term “planetary health.”38 Subsequently, the Rockefeller Foundation joined the Lancet in calling for a “new health discipline — public health 2.0.”39 The Wellcome Trust also enrolled in the project and launched a new priority area for funding, “Our Planet, Our Health.”40 Time will tell whether proponents can transform advocacy into meaningful political action and positive social change.