2100 has been estimated at one-in-a-million. Moreover, large supervolcano eruptions may cause a volcanic winter that could endanger the survival of humanity. The geological record suggests that supervolcanic eruptions are estimated to occur on average about once every 50,000 years, though most such eruptions would not reach the scale required to cause human extinction. Famously, the supervolcano Mt. Toba may have almost wiped out humanity at the time of its last eruption (though this is contentious). Since anthropogenic risk is a relatively recent phenomenon, humanity's track record of survival cannot provide similar assurances. Humanity has only survived 77 years since the creation of nuclear weapons, and for future technologies, there is no track record at all. This has led thinkers like Carl Sagan to conclude that humanity is currently in a "time of perils" – a uniquely dangerous period in human history, where it is subject to unprecedented levels of risk, beginning from when humans first started posing risk to themselves through their actions. Risk estimates Given the limitations of ordinary observation and modeling, expert elicitation is frequently used instead to obtain probability estimates. In 2008, an informal survey of experts at a conference hosted by the Future of Humanity Institute estimated a 19% risk of human extinction by the year 2100, though, given the survey's limitations, these results should be taken "with a grain of salt". Table source: Future of Humanity Institute, 2008. There have been a number of other estimates of existential risk, extinction risk, or a global collapse of civilization: Humanity has a 95% probability of being extinct in 7,800,000 years, according to J. Richard Gott's formulation of the controversial Doomsday argument, which argues that we have probably already lived through half the duration of human history. In 1996, John Leslie estimated a 30% risk over the next five centuries (equivalent to around 9% per century, on average). In 2003, Martin Rees estimated a 50% chance of collapse of civilisation in the twenty-first century. The Global Challenges Foundation's 2016 annual report estimates an annual probability of human extinction of at least 0.05% per year. A 2016 survey of AI experts found a median estimate of 5% that human-level AI would cause an outcome that was "extremely bad (e.g. human extinction)". In 2020, Toby Ord estimates existential risk in the next century at "1 in 6" in his book The Precipice: Existential Risk and the Future of Humanity.