An existential risk is a risk that threatens the destruction of the long-term potential of life.^[1] An existential risk could threaten the extinction of humans (and other sentient beings), or it could threaten some other unrecoverable collapse or permanent failure to achieve a potential good state. Natural risks such as those posed by asteroids or supervolcanoes could be existential risks, as could anthropogenic (human-caused) risks like accidents from synthetic biology or unaligned artificial intelligence. 

Estimating the probability of existential risk from different factors is difficult, but there are some estimates.^[1] 

Some view reducing existential risks as a key moral priority, for a variety of reasons.^[2] Some people simply view the current estimates of existential risk as unacceptably high. Other authors argue that existential risks are especially important because the long-run future of humanity matters a great deal.^[3] Many believe that there is no intrinsic moral difference between the importance of a life today and one in a hundred years. However, there may be many more people in the future than there are now. Given these assumptions, existential risks threaten not only the beings alive right now, but also the enormous number of lives yet to be lived. One objection to this argument is that people have a special responsibility to other people currently alive that they do not have to people who have not yet been born.^[4] Another objection is that, although it would in principle be important to manage, the risks are currently so unlikely and poorly understood that existential risk reduction is less cost-effective than work on other promising areas.

In The Precipice: Existential Risk and the Future of Humanity, Toby Ord offers several policy and research recommendations for handling existential risks:^[5]

• Explore options for new international institutions aimed at reducing existential risk, both incremental and revolutionary.
• Investigate possibilities for making the deliberate or reckless imposition of human extinction risk an international crime.
• Investigate possibilities for bringing the representation of future generations into national and international democratic institutions.
• Each major world power should have an appointed senior government position responsible for registering and responding to existential risks that can be realistically foreseen in the next 20 years.
• Find the major existential risk factors and security factors—both in terms of absolute size and in the cost-effectiveness of marginal changes.
• Target efforts at reducing the likelihood of military conflicts between the US, Russia and China.
• Improve horizon-scanning for unforeseen and emerging risks.
• Investigate food substitutes in case of extreme and lasting reduction in the world’s ability to supply food.
• Develop better theoretical and practical tools for assessing risks with extremely high stakes that are either unprecedented or thought to have extremely low probability.
• Improve our understanding of the chance civilization will recover after a global collapse, what might prevent this, and how to improve the odds.
• Develop our thinking about grand strategy for humanity.
• Develop our understanding of the ethics of existential risk and valuing the longterm future.