1. Nuclear war
After Hiroshima and Nagasaki, the world witnessed just how much of a threat nuclear weapons posed to humanity. The Cuban Missile Crisis and the Cold War saw the world poised on the brink of a wide-scale nuclear war. Since then, many other nations have developed nuclear weapons of their own, creating frightening implications for the future of our existence. Current political affairs make the idea of a global nuclear war a terrifying reality. The event of a nuclear war breaking out between two major world powers would result in the death of millions of people across the globe. However, the deadly threat is actually nuclear winter- soot from the nuclear firestorms settling into the stratosphere and causing a long-term cooling and drying of the world. Current climate simulations show that it could impede agriculture across most of the world for years. Recent research shows that this would lead to a global famine. If this scenario does occur, it would result in the starvation of billions. The scattered survivors left could be completely wiped out by disease. In the event of major nuclear war, the nuclear winter and global famine are said to be unavoidable. This is what makes it the biggest threat our species is currently facing.