My assumptions on different ways how the world can END!:

Solar storms

The sun follows an 11-year cycle that is currently building toward its "solar max," during which time the sun is more active. When solar storms occur, the sun can emit tides of electromagnetic radiation and coronal mass ejections, large bubbles of gas threaded with magnetic field lines. CMEs are essentially balls of plasma, and when they reach Earth, they release energy visible as colorful auroras. They may be pretty, but they unleash static discharges that can disrupt or knock out power grids. Solar flares, eruptions of supercharged protons, can reach Earth in minutes and also have catastrophic consequences.

NASA says modern power grids are so interconnected that a large sun storm could cause failures that would cut power to 130 million people in the U.S. alone. Outages would cost trillions of dollars and take years to fix, communications would be cut off, international trade might halt, and millions of people could die. Sound like science fiction? In 1859, a solar storm caused telegraph wires to short out in the U.S. and Europe, and in 1989, a solar storm knocked out power to all of Quebec, Canada. However, NASA predicts that the solar max that will occur in the 2012-2014 time frame will be average and says “there is no special risk associated with 2012.”

Pandemic

One of the most dangerous threats to the human population is a simple virus — that is, a deadly disease that spreads rapidly throughout the world. Within the last century we’ve had four major flu epidemics, as well as HIV and SARS, and scientists says it’s inevitable that another will occur. The 1918 influenza outbreak killed more people than World War I, and if a deadly contagion surfaced today, it could spread even faster and infect even more people. Considering how quickly diseases spread though all forms of modern transportation — and the amount of international travel that takes place today — an outbreak similar to that of 1918 “could have a more devastating impact,” says Maria Zambon, head of the Health Protection Agency's Influenza Laboratory.

And if nature doesn’t send such a deadly contagion our way, mankind just might. Biological warfare is another threat that looms over the modern world, and diseases like anthrax, Ebola and cholera have all been weaponized.

Planet X

Planet X, or Nibiru, is the supposed 10th planet in our solar system — if we're counting Pluto. According to the Planet X theory, Nibiru is enormous and is on a 3,600-year elliptical orbit that places it in Earth’s gravitational proximity in 2012 — an event that would cause flooding, earthquakes and worldwide destruction. Proponents of the theory cite earthquake and weather data as evidence of the planet’s increasing influence on Earth, and some say that Egyptian records show that the Planet X “flyby” corresponds to Noah’s great flood and the sinking of Atlantis.

 

However, astronomers say there’s no evidence to support Planet X theory and that if the planet did exist, humans would be able to see such a large planet with the naked eye. The Nibiru catastrophe was initially predicted to occur in May 2003, but the date was later changed to the infamous Dec. 21, 2012.

The Big Rip

According to Big Rip theory, our bodies, the planet and the entire universe will quite literally be torn apart. The theory’s chief proponent, Robert Caldwell of Dartmouth College, explains that the universe is expanding — driven by dark energy — and galaxies are moving farther and farther away from us. The rate of the universe’s expansion is also constantly accelerating like a vehicle that increases its speed by 10 mph for every mile it travels, and at some point, the acceleration becomes so fast that all objects are ripped apart.

Caldwell and his colleagues say they see no way to avoid the Big Rip if this acceleration continues; however there is a bright side: This apocalyptic occurrence won’t become noticeable for another 20 billion years, and scientists say that by then other events will have already destroyed our solar system.

Global warming

Whether you believe in man-made warming or not, there’s no denying the planet is getting hotter. In fact, 2010 tied 2005 for the warmest year on record with global temperatures 1.12 degrees Fahrenheit above the 20th century average. And there are some who say that we’re running out of time to stop irreversible climate change — in fact, by some calculations we’re less than a decade away.

According to climate scientists, once a critical greenhouse gas concentration threshold is passed, global warming will continue even if we stop releasing gases into the atmosphere. If this occurs, the Earth’s climate will become more volatile, resulting in catastrophic weather patterns. Plus, as temperatures rise, food will become scarce, air quality will worsen and diseases will spread. The World Health Organization estimates that 150,000 people are already killed by climate change-related issues each year, and U.N. Secretary General Ban Ki-moon has said that global warmingposes as much of a threat to the world as war.

Gamma ray burst

When a supernova explodes, it unleashes a massive gamma ray, or high-frequency electromagnetic radiation. Most of these huge bursts of energy take place too far away to harm Earth, but if one occurred within 30 lightyears from the sun — which is pretty close on the cosmic scale — it would be disastrous. The gamma ray would blow apart a portion of the planet’s atmosphere, produce worldwide fires and kill most of Earth’s species in just a matter of months.

However, the odds of a gamma ray burst destroying the planet are extremely low because not only would the supernova need to be close to Earth, the explosion would also have to be pointed in Earth’s direction. Fortunately, there are few high-mass stars with the potential to explode.

Computers take over

It may sound a lot like the plot of “The Terminator,” but computer technology is advancing daily and some believe that self-aware machines could become self-replicating and take over. After all, there are few areas of life where computers don’t intrude — they run banks, hospitals, stock markets and airports. Previously, computers were only as good as the humans using them, but artificial intelligence has the potential to create independently acting machines capable of outsmarting or destroying their creators.

Renowned scientist Stephen Hawking thinks computers could be a threat and argues that humans should be genetically engineered in order to compete with the phenomenal growth of artificial intelligence. In a recent interview he even said, “The danger is real that they could develop intelligence and take over the world.” The idea of a computer takeover may sound absurd, but you never know, we could be in the Matrix right now.

Electromagnetic pulse

Just as solar flares or coronal mass ejections could wipe out power grids, so could a sudden burst of electromagnetic radiation. The science is the same, but security experts say the cause is more likely to come from a more sinister source, such as the detonation of a nuclear weapon. An EMP blast — whether from a weapon or solar activity — could destroy our entire electronic, transportation and communications infrastructure in less than a second. If such a blast occurred over the United States, 90 percent of all Americans could be dead within a year, according to theCongressional EMP Commission.

The proximity of an EMP attack to the planet’s surface would affect the severity of its effects. This map illustrates how the United States would be affected by an EMP attack based on burst altitude.

Nuclear war

The Cold War is over, but the threat of nuclear war still exists today, with a number of countries possessing the capability of deploying such destructive devices. In addition to threats from the explosion and radiation, there are also indirect effects such as contaminated food and water supplies, poor air quality, destruction of power grids affecting communication and transportation, and nuclear winter.

It’s been theorized that detonating nuclear weapons will cause large amounts of smoke, soot and debris to enter Earth’s stratosphere, reducing sunlight for months or even years. Such a nuclear winter would result in severe cold temperatures and interference in food production. In 2007, scientists Brian Toon and Alan Robock concluded that if India and Pakistan were to launch 50 nuclear weapons at each other, the entire planet could experience 10 years of smoke clouds and a three-year temperature drop.