So you are having a bad day and feel that it can't get much worse. Well you have came to the right hub and you were wrong, it can get worse as we are covering the end of the world as we know it scenarios. Stop, before that puts you off and you hit the back button, DrWibble does not give you just all doom and gloom, he believes that us humans can foresee potential problems and work out possible course of actions to avoid them. So, also covered are the ways we are trying to avoid Armageddon.

This scenario is where there is an impact of a large extraterrestrial object with Earth. A common theory postulates that the extinction of the dinosaurs occurred approximately 65 million years ago when a large asteroid struck the earth, producing atmospheric dust which blocked solar energy and caused a significant lowering of temperatures worldwide.

However, do not despair since December 1995, the Near Earth Asteroid Tracking (NEAT) program run by NASA and Jet Propulsion Laboratory to discover near-Earth objects has been action. So at least we will have time to put on a fresh pair of underpants before it hit.

NASA's goal over the next few years is to discover at least 90 percent of all near-Earth objects with diameters larger than one kilometer. Working in coordination with several teams around the world they routinely search the skies for as-yet undiscovered asteroids and comets. If a near-Earth object with a potentially hazardous orbital path is discovered, additional observations are made to give a better estimation of its orbital path. Due to Newton's theory of gravitation, scientists calculate the orbital motions of all newly discovered objects to see if they present a risk into the future.

If an object were to threaten Earth, it would only be necessary to move the object by one Earth radius, a very small distance in space terms if discovered early enough. One idea suggested for a smaller asteroid is to anchor a shuttle-type engine onto the moving space rock and gently speed it up or slow it down. Another possible strategy would be to attach solar sails to a potentially hazardous body and allow the gentle pressure of sunlight to deflect the threatening asteroid away from Earth. Anyway you have seen the movies, so you get the picture.

http://neo.jpl.nasa.gov/index.html

A pandemic taken from the Greek words pan all and demos people is a spreading of infectious disease that propagates through populations across a large region;

The World Health Organization (WHO) responsible for directing and coordinating authority for health within the United Nations system states that a pandemic can start when three conditions have been met:

• Emergence of a disease new to a population.
• Agents infect humans, causing serious illness.
• Agents spread easily and sustainably among humans.

An example of a pandemic is the 1918 deadly influenza pandemic. It ended within 18 months but over that time some 50 million were dead; some estimates put the total of those killed worldwide at over twice that number. More information on this modern pandemic can be found on Londongirl hub.

http://hubpages.com/_wibble/hub/Spanish-Flu-historical-event-or-precursor-of-H5N1-Bird-Flu

Right, so DrWibble you promised me it won't be all doom and gloom, where is the helpful stuff. So what can you do to help in a pandemic, unless you are a microbiologist and can reverse engineer the virus, create a vaccine, ramp up production and distribute to the general population, the best way to limit the spread is by

• Social distance. Travelling less, Working from home if possible or avoiding contact with crowds, so there is less opportunity for the virus to spread.

• Respiratory hygiene. Be aware of the need for respiratory hygiene covering mouth when coughing or sneezing, careful disposal of contaminated tissues or other materials.

• Masks. No mask can provide a perfect barrier but products that meet or exceed the NIOSH N95 standard recommended by the World Health Organization are thought to provide good protection. WHO recommends that health-care workers wear N95 masks and that patients wear surgical masks. Any mask may be useful to remind the wearer not to touch the face. 

• Hygiene. Frequent hand washing, especially when there has been contact with other people or with potentially contaminated surfaces can be very helpful. Alcohol-based hand sanitizers also kill both bacteria and viruses.

In the future, pandemics hopefully should become less of a risk with the advancement of science we are beginning to understand the inner workings of these viruses and able to model the spread through the population. Once, we know detailed information about them we can work out strategies of eliminating them.

Throughout the Earths history there has always been climate change, in this end of the world scenario we take climate changes as the environment become to hostile to support current human life populations. Political and public debate continues regarding the appropriate response to global warming but it is generally thought to be a result of human behaviour rather than due to natural changes in the environment.

The available options are

• Mitigation to reduce further emissions from current industry
  
• Adaptation to reduce the damage caused by warming
• More speculatively, geoengineering to reverse global warming.

Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions. The regular use of renewable energy is becoming increasingly available to try and reduce gas emission from fossil fuels.

Since the creation of the atom bomb in the 1940's, there has been a new threat to mankind, nuclear war. Nuclear warfare strategy is to either fight or avoiding a war. The policy of trying to ward off a potential attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence or mutually assured destruction (M.A.D.)

If there was an exchange of missiles (for example a war between India and Pakistan) would plunge the planet into temperatures colder than the Little Ice Age (approximately 1600ad-1850ad). This would be essentially take effect immediately with impact on agriculture. Larger amounts of smoke form a big exchange of missiles would produce larger climate changes, and produce a true nuclear winter, making agriculture impossible for years. In both cases, model simulations show that the effects would last for more than a decade.

So, apart from building a nuclear bunker in your garden with a decades worth of food on hand, the best way to avoid is understand each countries values and culture, to form links so our economies become some intertwined it is not beneficial to go to war with each other.

Nanorobots (nanobots, nanoids, nanites or nanonites) are typically concieved to be devices ranging in size from 0.1-10 micrometers and constructed out of nanoscale or molecular components. As no artificial non-biological nanorobots have yet been created, they remain a hypothetical end of the world concept.

Gray goo phrase is given to the concept of out-of-control self-replicating robots consume all matter on Earth while building more of themselves. The term grey goo is usually used in a science fiction context. In the worst postulated scenarios, the Earth would also be turned into goo (with goo meaning a large mass of replicating nanomachines lacking large-scale structure, which may or may not actually appear goo-like). The disaster is posited to result from a deliberate doomsday device, or from an accidental mutation in a self-replicating nanomachine used only for other purposes, but designed to operate in a natural environment.

However, the good part of this end of the world scenario is that science and engineering is not quite yet at a point of testing this end of the world scenario. Additionally, due to their size a possible denfensive strategy would  be disabling or destroying a working nanoreplicator by concentrating heat on it.

To conclude, as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns -- the ones we don't know we don't know.

It is the unknown unknowns end of the world scenarios we have to be worried about, unfortunately this hub can't help you there, so don't have nightmares and keep calm and carry on.