My father’s family came to the US in the 1930s, a Jewish family fleeing Nazi Germany. My life has gone well, and I suppose I should be grateful for the way things turned out. However, I can’t help but wonder what would the world look like today if the Holocaust and World War Two had never happened. All those people who died – would they have living descendants? Would they have lives like mine? Would I be friends or neighbours with some of them? Would I even have been born?

When people think about catastrophes that cause loss of life, they almost always think only of the immediate harm caused. Over 50 million people died in WWII, around 15 million in World War One, and around 160,000 in the 2010 Haiti earthquake. But these figures leave out the long-term effects of catastrophes – the people who never had a chance to live, the ways that our world would be different. These ramifications can be harder to document. But that does not make them less important.

Indeed, if we take a step back and look at the long-term view we can see that certain catastrophes – the largest ones – are among the most important events in the history of the world. The Cretaceous–Paleogene (K-Pg) extinction event 66 million years ago wiped out the dinosaurs and freed up space for little mammals like us. Long before that, the Oxygen Catastrophe of 2.5 billion years ago destroyed most anaerobic life and set the stage for us oxygen-breathers. Had these catastrophes not occurred, humans and many other modern species would likely never have come into existence.

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That’s why I and other researchers who study global catastrophic risk believe that avoiding these events should be one of our biggest priorities for the 21st Century.

Human activity has made this era of Earth’s history among the most perilous ever. And if we consider the impact on our species thousands of years hence, avoiding a global catastrophe is not just about preserving people’s lives today – it is about protecting our future, our potential, and the billions of descendants whose paths would be altered forever.