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). This paper highlighted "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" (Dunk & Jones, Sounding the alarm on climate change, 1989 and 2019," New Engl. J. Med., 382 (2020) 205-07.).