On October 15, 2016 in Boston attendees were ‘Contemplating the Unthinkable!’ The one-day symposium on “Climate Change and the Growing Risk of Nuclear War: A healthcare perspective” examined the catastrophic public health consequences of climate change and the ways that climate change will increase the risk of conflict, including nuclear war. While there are many enormous public health threats facing humanity today, two of them, climate change and nuclear war are unique in the existential threat they pose to human civilization and the survival of our species. Physicians for Social Responsibility, supported by our global federation, the International Physicians for the Prevention of Nuclear War, explored these important links between the two at the successful symposium at the Tufts University School of Medicine's Sackler Auditorium. Speakers included: • Ira Helfand, MD, co-President, IPPNW • Bill McKibben, Middlebury College, 350.org • Dr. Zia Mian, Princeton University • Jennifer Leaning, MD, SMH, Harvard T.H. Chan School of Public Health • Barry Levy, MD, MPH, Tufts University School of Medicine • Catherine Thomasson, MD, Executive Director, Physicians for Social Responsibility This event was livestreamed and lectures can be found here.