Possibilities refers to possible scenarios which may ultimately cause an end to our civilization? These scenarios don't necessarily have to be high-profile disasters. Some can happen relatively slowly, and unnoticed by most. Some, however, can happen suddenly...catastrophic events that change life as we know it virtually overnight.
Click on each bulleted Event to read more about it.Catastrophic Events
The Earth is in a cosmic shooting gallery. Millions of objects of 30-50 meters in diameter (the size of the object that caused Meteor Crater in Arizona) are likely cruising around the sun in orbits that cross Earth's orbit. One object, 2011 MD, passed the Earth at a distance of about 12,000 miles (very, very close by cosmic standards), on June 27, 2011. This 10-45 meter diameter asteroid was found on June 22, 2011! A whole five days warning.
99942 Apophis is a 320-meter asteroid that crosses Earth's orbit on every one of its own. It was discovered in 2004, causing quite a stir, because scientists initially gave it a 1-in-60 chance of hitting the Earth on its April 13, 2029 pass. 1-in-60! That's five times more likely than being killed by someone with a gun (1-in-306). It is even better odds than dying in a car crash (1-in-88).* They have since got a better look at its orbit, and have decided that it WON'T hit in 2029...at least that's what they're telling US. A rock this size would certainly cause some damage. With an estimated impact energy of 850 megatons, it could cause devastation to an area the size of Texas if it hit land, or spawn significant tsunamis on a (more likely) water strike. It wouldn't likely start an "Impact Winter," but we'll know we've been hit.
While 99942 Apophis is unlikely to cause TEOTWAWKI, there are others out there that might. It is estimated that we know about approximately 80% of those NEO's of 1km in size or greater. We know of substantially fewer of those NEO's smaller than 1km in diameter. We're not likely to have much warning on the one that gets us.
There are currently six supervolcanoes that can be considered active. Three of these are located in the U.S., with three more spread out across the world. The largest is the Yellowstone Caldera, a volcanic crater 1500 square miles in area. The others are the Long Valley Caldera in east-central California and the Valles Caldera in northern New Mexico, Lake Toba in Indonesia, Taupo Volcano in New Zealand, and Aira Caldera in Japan.
If any of these were to experience a major eruption, it would cause massive destruction and a change to our civilization. To provide an illustration of the power of these volcanoes, Mount Saint Helens, in Washington State, erupted on May 18, 1980, with the force of 24 megatons of TNT, ejecting approximately 2.8 cubic kilometers of material from the mountain. This was the most destructive volcanic eruption in United States history. In the scope of things, though, Mount St. Helens is small potatoes. The island of Krakatoa in Indonesia exploded in 1883 with a force of 200 megatons of TNT, destroying two-thirds of the island, and ejecting about 21 cubic kilometers of material. Mount Tambora (also in Indonesia) erupted in April, 1815, blowing the top third off the mountain with a force of 800 megatons of TNT and ejecting about 160 cubic kilometers of material across Sumbawa Island, and into the stratosphere.
This last eruption, combined with other smaller eruptions from the few years prior, contributed to the Year Without a Summer, as the summer of 1816 was known. The high altitude ash from Sumbawa Island allowed less sunlight to penetrate to the ground, causing weather anomalies and crop failures in Western Europe and North America. Crop failures caused the prices of grains, meat, and dairy products to rise sharply, which led to famine and food riots. Disease followed in famine's wake.
Even Mount Tambora and the world-wide impact of it's eruption are insignificant compared to the effect a supervolcanic eruption. Yellowstone's last eruption some 640,000 years ago ejected about 1000 cubic kilometers of material. An eruption like that today would bury North America in ash and cause a "volcanic winter," shutting out the light of the sun for years. Even an eruption of of the Indonesian, New Zealand, or Japanese supervolcanoes would probably end our civilization.
Periodically, intense solar activity will cause a large mass of particles from the sun's corona to erupt into space. Each CME can release up to 100 billion kg of matter, at up to 3200 km/second (with an average speed of 1000 km/second). If the eruption is lined up just right, that means this super-charged plasma could slam into Earth within two days or in about 13 hours for the fastest CMEs. This direct hit is called a "Halo" event (because it looks like a halo around the sun as it approaches Earth).
The number and speed of CME's during any month is highly variable. 7500 CMEs occurred between 1996 and 2003. More CMEs tend to occur during periods of high sunspot activity, though no direct causal connection has been observed. From January, 1996 through May, 1999, there was an average of one halo CMEs per month. On the other hand, from June, 1999 through June, 2003, there were four halo CMEs per month. Maximum sunspot activity occurs on an approximate 11-year cycle. 1990-1991 were years of maximum sunspot activity, as were 2000-2001. We are currently in a maximum. Spaceweather.com shows the number of "Spotless Days" of each of the last few years. 2009 had 290 Spotless days, meaning the sun was very quiet. 2010 had 51 Spotless days, 2011 had 2 Spotless days, and we haven't had a Spotless day throughout January 2012.
On January 27, 2012, Sunspot 1402 issued an extreme ultra-violet flash and produced a spectacular CME. Luckily, Sunspot 1402 was rotating onto the far side of the sun, so the CME was basically at a right angle to the Earth, as seen in this animation. This CME traveled at approximately 2500 km/sec. This means the wave-front of particles reached the Earth's orbit in about the same time the famous Carrington Event did in 1859.
So what happens when we are hit by one of these masses of super-energetic particles? First, the interaction of the charged particles and the Earth's magnetsphere cause it to deform, and cause larger than norm auroras to form. A Halo CME last October caused the aurora borealis to be seen as far south as Alabama.
Other, stronger effects can and have happened due to a direct CME strike:
And these things happen during normal solar storms and halo CMEs (remember, there is at least one halo CME event a month, even in periods of low solar activity). The last effect is the most critical for our purposes. A sufficiently strong CME striking Earth could very well plunge the planet into darkness, both literal and metaphorically.
Our society is so integrated with, and dependent upon, electronics that a Carrington-class event or larger could wipe out a significant portion of the planet's transformers, bringing electrical transmission to a halt. No electricity, no lights. Water and sewer depend on electricity, as do food and fuel deliveries. Looters and other criminal elements will be the first to take advantage of the blackout, and as the power outage continues into weeks and, conceivably, months, ordinary people who are now desperate from hunger and thirst will begin to run amok.