Seventy-five years ago yesterday, at 8:15 in the morning, the United States dropped an atomic bomb on the city of Hiroshima. The fireball charred every human being within two kilometre of the blast. Seventy-one thousand people died instantly. Ultimately, another 70,000 would follow them. Three days later, a second bomb obliterated Nagasaki. Thus was humanity introduced to the nuclear age.

In 1947, the Bulletin of the Atomic Scientists, founded by scientists who had helped develop the weapon, created the Doomsday Clock. The clock signifies the threat to humanity of nuclear weapons and, more recently, climate change. The decision to move the minute hand is made by the Bulletin’s Science and Security Board in consultation with its Board of Sponsors, which includes 13 Nobel laureates.

Set at seven minutes to midnight in 1947, the clock had moved up to two minutes by 1953 with both the United States and the Soviet Union testing hydrogen bombs. It was subsequently moved back to six minutes due to increased cooperation between the two nuclear powers and then to 12 minutes with the Partial Test Ban Treaty. When France and China acquired nuclear weapons it shifted ahead five minutes. With the end of the Cold War and the signing of the Strategic Arms Reduction Treaty, the clock hit its safest point ever, 17 minutes to midnight. Then the situation began to deteriorate with nuclear tests by Pakistan, India and North Korea.

Things have gone from bad to worse. All the nuclear states are modernizing their arsenals. Arms control and disarmament treaties are crumbling. Most recently, the United States, the only nation to actually use nuclear weapons, has withdrawn from the nuclear accord with Iran, suspended compliance with the Intermediate-Range Nuclear Forces Treaty, abandoned the Open Skies Treaty, and is considering resuming nuclear testing.

The keepers of the clock have now moved the hand the closest to midnight it has ever been—100 seconds. As the clock ticks down, we inch ever closer to unleashing “the destroyer of worlds.” As if global warming and a pandemic weren’t enough.