Anthropic shadow is the phenomenon involved when attempts to estimate the probability of a global catastrophe are biased by the fact that they are implicitly conditioning on the existence of human observers.

A severe enough global catastrophe that destroys all present observers and prevents the emergence of any future observers will necessarily leave no observable traces of its past existence. Such an anthropic effect will bias any attempt to estimate existential risk based on observed frequencies, causing an underestimation of actual risk.

Milan Ćirković, Anders Sandberg and Nick Bostrom have developed a model to understand and correct for this effect (Ćirković, Sandberg & Bostrom 2010)