This is an overview of scenarios in which a global catastrophic risk creates harm. Some sources of catastrophic risk are anthropogenic (caused by humans), such as global warming, environmental degradation, engineered pandemics and nuclear war. On the other hand, some risks are non-anthropogenic or natural, such as meteor impacts or supervolcanoes. The impact of these scenarios can vary widely, depending on the cause and the severity of the event, ranging from temporary economic disruption to human extinction. Many societal collapses have already happened throughout human history.