A natural disaster is, simply put, a disaster which is unaffected by the actions of humanity so cannot be prevented by many ordinary scale human measures. This could be an earthquake, hurricane, tornado or similar newsworthy phenomenon, or it could be something more commonly considered science fiction than fact, such as an asteroid impact or supervolcano eruption.
Extinction Level Events
A global catastrophe such as an asteroid collision or supervolcano eruption- sometimes called Extinction Level Events or ELEs- could hasten this demise as it is believed to have done with the dinosaurs. An asteroid or comet as small as two kilometres in diameter could in theory raise enough dust from a ground impact to introduce a global winter by blocking the Sun’s rays (Morrison, David, 2004), and the detection, destruction or deflection of such near Earth objects or NEOs is extremely difficult even with current spaceflight technology.
Supervolcanoes
It is known that underneath the Yellowstone National Park in the USA lies one of the largest supervolcanoes in the world, dormant for now but nonetheless likely to erupt, and there are several similar volcanoes around the world. The risk of a super-eruption is considered nearly five to ten times more likely than a NEO impact and would have similar effects (solcomhouse.com), but with the added consideration that there is no way to prevent such a calamity, even in theory, with current or immediately foreseeable technology.
Cosmic Destruction
Extreme natural disaster scenarios include the passage of a black hole into the solar system or the possible effects of the Earth’s magnetic poles reversing. The latter is in fact considered by most geophysicists to present only a very minimal danger to life, as “human beings have been on the Earth for a number of million years, during which there have been many reversals, and there is no obvious correlation between human development and reversals. Similarly, reversal patterns do not match patterns in species extinction during geological history” (Geomag.bgs.ac.uk). The consumption of the solar system by a travelling black hole is of course possible, but so far out of human control that any attempts to prevent or foresee the event with current technology would be irrelevant.
Natural disasters occur on a non extinction level with a fair amount of regularity, with a recent example being the earthquake in Haiti in 2010 which has a current death toll of around a quarter of a million people, with more bodies being found seemingly every day. The idea of such an event happening on a global scale, with nobody left to provide support or aid to any survivors, may seem ludicrous in everyday life but is a lot less impossible than many would believe.
Resources
Morrison, David, 2004. "Asteroid and Comet Impact Hazards,” NASA Ames Research Centre, impact.arc.nasa.gov accessed 22/02/10.
Solcom House, "Yellowstone Supervolcano." Solcom House, solcomhouse.com accessed 22/02/10.
British Geological Survey Team, "Magnetic Flip." Geomag.bgs.ac.uk accessed 22/02/10.
Associated Press, "Haiti raises quake death toll" online at MSNBC accessed 22/02/10.
