Final answer:
NEOs, such as comets and asteroids, pose a global catastrophic risk, and are the only natural disasters that we have the potential to prevent through technological means like kinetic impact and nuclear explosives, pending early detection.
Step-by-step explanation:
Near-Earth objects (NEOs) such as comets and asteroids are celestial bodies that come close to our planet and can potentially cause global catastrophes. Impacts from these objects, as highlighted by Harvard paleontologist Stephen Jay Gould, could have profound effects on the evolution of life by challenging the survival of species in ways beyond natural selection and adaptation to changing environments.
Human populations, now more numerous and occupying vulnerable areas, are at an increased risk of being affected by natural disasters, including NEO impacts. However, NEO impacts are unique among natural hazards because, through advanced technology and astronomical surveys, we potentially have the means to prevent them entirely. Technologies under consideration for defending Earth include kinetic impact by spacecraft or nuclear explosives to alter the NEO's trajectory.
International efforts, such as those by the United Nations, and scientists are focusing on early detection of NEOs to enable timely defensive actions. Though no NEO on a collision course with Earth has been found, continued monitoring is imperative.