The funny thing about life is, trouble never comes from where you expect it. You spend two months worried about interviewing for that big job promotion, then on your way there, you get attacked by a pack of wild dogs. That's just the way it goes.
So in terms of worldwide disasters, while Hollywood obsesses over asteroid strikes and earthquakes and whatever the fuck 2012 was about, don't be surprised if disaster comes in the form of one of these lesser-known calamities that you'd never even heard of.
Until today, that is.
Volcanoes are badass, there is no denying that. People worship the things as gods. They can create damned land masses. And sure, Mt. Pinatubo and Krakatoa may have messed some shit up when they went off, but that's really just a problem for the people who made the rather short-sighted decision to live at the base of one.
Whatever, mountain god. We live over here.
But what if you had a really, really big volcano. A super volcano, if you will. One big enough to fuck up the whole planet.
Supervolcanoes exist, and they are to volcanoes what nuclear weapons are to firecrackers. According to Wikipedia, a supervolcano can puke out more than 240-cubic-miles of matter into the sky, which is millions of times larger than a normal eruption.
Imagine tossing all of Connecticut into the atmosphere.
They are caused by massive amounts of magma building up pressure under the crust, and not enough holes (volcanoes, geysers, etc,) to vent it all. Eventually, the pressure builds until a massive section of earth explodes. The human race was possibly shaped by one such explosion--it wreaked such havoc on the ecosystem that when it was done, there were only enough humans left on the planet to fill one high school gymnasium.
So Are We Doomed?
Maybe. There is no evidence that any of these are going to explode in our lifetime- oh wait. Long Valley in California has been showing signs of "waking up" in the past 20 years.
Foul play hasn't been ruled out.
Then there are the Siberian traps in Russia, which are quiet for now. This is very good news because it is estimated that if they blew up, they would likely cause another event like the one back at the Permian Triassic boundary 251-million-years ago... which virtually wiped out all life on Earth.
You know how every once in a while you hear a story about some dumbass who fires his gun into the air like Yosemite Sam, only to have the bullet fall back to Earth and kill some bystander a few seconds later?
Imagine if the Earth did that, only instead of a bullet, it's a hunk of rock big enough to kill millions of us. That's a verneshot.
Also called God's Money Shot.
It all starts the same as your mega-volcano up there, when incredibly hot rock starts welling up under the Earth's crust. Only this time, the heat creates a massive buildup of carbon dioxide gas underground. It builds and builds and builds until it erupts with such incredible force that it launches gigantic rocks into fucking space.
Well, not all the way into space. If that's all it did, it wouldn't be such a problem (and in fact we'd probably just sell tickets to that shit--though you'd have to be far enough away to avoid the shockwave and molten rock spraying everywhere). No, the problem is the rock doesn't quite wind up leaving the atmosphere or settling into orbit. So your real troubles start when it comes back down.
So Are We Doomed?
We don't know for sure that this has ever happened, but if it did, it would basically combine all of the horror of a supervolcano with a massive asteroid strike.
The whole theory came about because when looking back over some extinction-level events of the past, you seem to have both signs of an asteroid strike and a volcanic eruption. And that would be such spectacularly bad luck that it would not only confirm the existence of deity, but of an extremely pissed off deity.
So it seems much more likely to some experts that instead of a rock from outer space, that the call was coming from inside the house, so to speak--a hunk of our own planet came crashing down thousands of miles away. It would seriously be like if you were just minding your own business tomorrow and suddenly Tokyo fell on your head.
In case you didn't know, the Gulf Stream is a sort of a "river" in the Atlantic ocean, a current of water that runs from Florida to western Europe. It has existed for thousands of years, and pumps warm water and air up to western and northern Europe, places that would otherwise be (more) frozen hell-holes.
You're welcome, Finland.
Scientists have noticed, however, that the overall temperature of the stream seems to be dropping, and has dropped a pants-shitting 30 percent since 1992. As you probably guessed, we again have climate change to thank. Before someone in the comments screams, "OH SO NOW GLOBAL WARMING MAKE PART OF THE OCEAN COOLER?!?!?!" keep in mind that when hot air melts a glacier, the hunks of ice break off and cool the water they melt into.
Originally, the fear was that if the Gulf Stream cooled too much, it would stop running, since it's those differences in temperature that keep it going. Then western and northern Europe would once again become home to woolly mammoths and fanged squirrels.
Artist's rendering from a U.N. report
However, studies have shown that if the Gulf Stream were to stop, there appear to be enough other factors warming Europe that it would have an effect, but wouldn't be the end of the world. So hell, why did we even bring it up?
The sudden drop off in inappropriate Speedo wearing in Europe would be the least of our concerns. According to measurements taken in 2005, the possible side effects of a "thermohaline shutdown" could include massive climate shifts, increases in major storms, greenhouse gases collecting in the upper ocean and phytoplankton dying off. In other words, Soylent Green would move from "Charlton Heston wailing" to "Grim predictor of the future."
In case you haven't seen this 37-year-old movie, Chuck discovered we were eating humans because we ran out of food, and we ran out of food because we killed the fucking ocean. So it would be like that, only with cataclysmic El Ninos.
So Are We Doomed?
Like with a lot of effects of climate change, we're kind of counting on uncertainty to save us (that is, we don't know exactly how this will work because we've never seen it happen before). Models show the current should keep running for another hundred years or so and they could still wind-up having to adjust those predictions--in either direction.