“The subject of climatic and environmental changes that result from human activity has been much in the news recently,” Alexander Leaf wrote in the Journal 30 years ago.1 Threatened by acid rain, greenhouse gases, ozone depletion, and global warming, the planet seemed vulnerable. Humans would face “disastrous consequences” as the planet ruptured around them. Leaf was sounding the alarm on climate change and human health: environmental change had become part of the burden of physicians. Now, as the climate crisis continues to unfold, the story of a physician who devoted his attention first to the nuclear threat and then to planetary health offers much-needed inspiration.

Leaf was born Alexander Livshiz in 1920, in Japan, where his parents had fled the Russian Revolution. After migrating to the United States, he studied chemistry at the University of Washington, joined the Army Medical Corps, and completed an accelerated medical degree at the University of Michigan in 1943. After residencies at Massachusetts General Hospital (MGH) and the Mayo Clinic, he returned to Michigan to research electrolyte metabolism, including how bodies responded to hot climates. With support from the Rockefeller Foundation, he established a cell biology laboratory at Harvard Medical School (HMS). In 1966, he became the Jackson Professor of Clinical Medicine at Harvard and chief of medicine at MGH.

Living in the shadow of nuclear war, Leaf helped found Physicians for Social Responsibility (PSR) in 1961 and became a prominent member of International Physicians for the Prevention of Nuclear War (IPPNW). Both groups called on physicians to extend their vision beyond the clinic. As Leaf later wrote in his memoir, “there are social and man-made hazards with possibly disastrous consequences to human health” that were ignored by medical training. To protect human health, physicians had to educate themselves about those hazards and take their stand “in the vanguard.” Physicians in PSR, for instance, saw that there could be no useful medical response to nuclear war. They therefore worked to prevent it, in part by cataloguing the likely human consequences, both physical and psychological, of such “genocidal destructive forces.”2 By the early 1980s, PSR had established a significant public presence and won substantial political clout.

In 1981, Leaf became chair of the new Department of Preventive Medicine and Clinical Epidemiology at HMS. Work with the World Health Organization (WHO) had shown him what physicians could achieve by means of education. He was also influenced by evolutionary perspectives on disease and medicine. He cited the work of Johns Hopkins pediatrician Barton Childs, who argued that evolution had left humans ill suited for their modern environment and that physicians should first focus on environmental and lifestyle factors, turning to medicines or surgery only as a last resort. Leaf’s department explored nutrition, occupational health, environmental health, epidemiology, and prevention of infectious disease. He was disappointed to find that many students preferred to learn “the cold dope” — traditional diagnosis and therapeutics.2

Leaf’s interest in the health effects of nuclear war, which led to contributions to a 1984 WHO report and a 1985 Institute of Medicine symposium, increasingly focused on the consequences for global ecosystems. In 1986, he published an update on the medical consequences of nuclear war, highlighting new research on estimated casualties, the effects of radiation, and post-blast immune dysfunction. A full third of the article examined what looked to be the most deadly consequence of any nuclear war: global starvation. Food reserves would be contaminated or plundered, technologies for harvest, transportation, and refrigeration would fail, and radiation would disrupt ecosystems.3

This ecologic approach to human health led Leaf beyond the nuclear threat. He heard Michael McElroy, at Harvard’s Center for Earth and Planetary Physics, lecture about the threat of global environmental change. He read reports from the Worldwatch Institute. He was inspired by the World Commission on Environment and Development, led by physician and Norwegian Prime Minister Gro Harlem Brundtland. The commission’s 1987 report called for decisive multilateral action to secure the “common future” of the human species. Human activity had already begun to disrupt the planetary systems that support life. Leaf saw that preventive medicine would need to address not only the nuclear threat, but also the environmental degradation taking place globally.

Leaf might also have seen an April 1989 Lancet editorial entitled “Health in the Greenhouse.” It warned of a global environmental disaster on the order of an AIDS pandemic or a nuclear war — but more certain, since it proceeded from physics rather than politics. There was no time for further research, the editorial argued. Fundamental changes had to be made in transportation, energy, and agriculture to protect the ecosystems on which human survival depended.4

Leaf shared his environmental concerns with his close friend Arnold Relman, the Journal’s editor-in-chief at the time. Relman had warned IPPNW physicians that they should avoid committing themselves to political parties or specific solutions even as they outlined threats to human health. Yet he encouraged Leaf to write up his concerns for publication in the Journal.2 Leaf’s December 1989 article, “Potential Health Effects of Global Climatic and Environmental Changes,” suggested that climate change’s effects on bodies, minds, and ecosystems would be analogous to those of nuclear war. Physicians had to explore not just environmental science, but also the social, economic, and political factors that drove environmental change, influenced the distribution of its health effects, and held the key to possible solutions.1

Leaf’s article introduced these problems to a wide readership in medicine and public health and inspired scholarship in many fields. As the Cold War wound down, Leaf and his colleague Eric Chivian, a Harvard psychiatrist, campaigned successfully for PSR to adopt “a broader environmental protection plan.”2 Harvard continued to be a base for new thinking about health and the environment and is now home to the Planetary Health Alliance, led by physician Samuel Myers.

Over his career, Leaf had turned from one existential threat to another, from the risk of nuclear annihilation to catastrophic effects of global environmental change. He retired in 1990 but never lost sight of the global environment as the context for human health. His 1996 memoir engaged with new research on human health on an ailing planet, showing language and themes similar to those of the work of epidemiologists Anthony McMichael and Andy Haines.5 “The ultimate consequence to mankind of such environmental damage,” he wrote, “will be deleterious effects to human health.” IPPNW had won the Nobel Peace Prize in 1985 for its efforts to educate and advocate, contributions that had helped to cool — though not end — nuclear tensions. Leaf believed that education and advocacy would also prove effective against climate change: if people understood the health threats of environmental degradation, they would “personalize the consequences of these threats to their own health and survival and demand appropriate controls through government regulations.”2

The alarms sounded by Leaf, the Brundtland Commission, and others spurred ongoing research and advocacy. Scientists have produced irrefutable evidence of climate change and environmental degradation. The past decade has seen a rush of new organizations, new journals, and new funding priorities loosely united under the mantle of “planetary health.” Their goals align with Leaf’s 1989 agenda, calling for reconfiguration of transportation, housing, agriculture, energy, and medicine to sustain the planet’s natural systems and the health of humans and other species.

But the climate crisis might prove more intractable than the nuclear threat. Prevention of nuclear war requires sustained commitments by world leaders. Public pressure can be brought to bear directly on them. Prevention — or, at this point, mitigation — of climate change requires fundamental restructuring of all societies. Everyone, not just political leaders, must act. It may no longer be appropriate for physicians to remain apolitical. Leaf’s “potential health effects” are now being realized. Many climate-conscious physicians and planetary health researchers call for change through existing political mechanisms. Will such actions go far enough or fast enough? Seeing their warnings go unheeded, activists have turned from research to advocacy to civil disobedience. They promise to sound the alarm on climate change and human health ever more forcefully until our societies are transformed.