what kind of natural disaster can affect earth on a planetary scale?

Question

Our world is surrounded by a metaphysical barrier that separates us from other dimensions and the things which inhabit them. This barrier is made up of 7 layers, with the last one being the closest to our realm. An ancient deity that exists across multiple dimensions is prophesized to enter our world and conquer it. In order to accomplish this, he must pass through the six layers separating our dimensions from his. The final layer would collapse with his birth into the mortal realm as a human child. A cult devoted to this prophesy has been operating since the beginning of mankind's history to bring about this event.

Throughout our 10,000 year history on this planet, the cult influenced certain events at different points in various time periods, shaping world history and slowly breaking down the barrier layers. When the king was finally born, it sent a metaphysical "tear" through the final layer of our realm, causing a devastating calamity. This natural disaster was felt worldwide and resulted in the deaths of millions of people.

When I look through history, the deadliest natural disasters are region specific, them being earthquakes, floods, etc. What I am looking for is a natural disaster whose effects can be made manifest on a global scale. I don't want something apocalyptic or world-ending. Society should still be functional and carry on, with some places obviously more affected than others. Nevertheless, I want the death count to be staggeringly high enough and on a global scale so that most continents experience some part of it. My focus is on:

1. What natural disaster would fit this bill
2. Where should it begin on the planet in order to have the maximum impact
3. What must happen in order for it to be started.

How can I make this work?

Answer 1

When I look through history, the deadliest natural disasters are region specific, them being earthquakes, floods, etc.

This is probably because you were looking at the wrong things.

The first thing off the top of my head would be a major volcanic event. You've probably looked at these, glanced at the scope of the destruction from the eruption and immediate secondary effects and decided that was it.

Not so.

Major volcanic events have significant effects on Earth's environment, with far-reaching and long-lasting consequences. Have a look at almost any eruption at Volcanic Explosivity Index 7 for example (though don't bother looking at 8, given that you don't wan't apocalyptic levels of destruction).

The Laki eruption in Iceland in 1783 was not a massively explosive event, but it carried on erupting for months and was catastrophic for the population of iceland. Further afield though, the climatic disruptions resulted in famines across the world, hazardous weather patterns and a bitterly cold winter.

The 1815 eruption of Tambora resulted in the Year Without a Summer. The 1883 eruption of Krakatoa resulted in record rainfalls (with accompanying dramatic flooding) and snow falls (with associated damage and agricultural issues) and bitterly cold winters across the world.

What you need, then, is a major eruption and subsequent global climatic event, triggering famine, mass migration, and pushing unstable political situations over the edge into warfare, civil and otherwise. Health systems pushed to the limit, power generation capacity overwhelmed by the need for heating, that sort of thing. You don't need to be swallowed by a mudslide for a volcanic eruption to kill you.

For maximum effects from the eruption itself, make sure there's a megatsunami to go along with it. Bonus points if it happens in the Atlantic, where coastal populations are largely unaware of the risks and have no training, preparation or defensive mechanisms in place. Cumbre Vieja might be a nice starting point, though the chances of it forming a megatsunami or an eruption large enough to seriously affect global climate seems dubious but hey: your cause isn't rooted in reality, so you can handwave it. There are lots of Pacific sites which are more plausible sources, and if the tsunami is big enough all the planning and preparation in the world aren't necessarily going to save you and the resulting devastation will not be easily fixed.

Answer 2

Coronal Mass Ejection

A coronal mass ejection (CME) can be devastating. Although CMEs like the Carrington Event would not directly result in a loss of life, but could knock out all electricity across the entire planet, which could have taken up to a decade and $2.6 Trillion USD to recover from, there's no saying that CMEs can't be larger.

An even larger CME could (theoretically, as we have no historical example of it) cause a gigantic, world-wide magnetic superstorm. Imagine, if you will, lightning blasts across the entire earth for hours or days at a time, with no electricity, and super-charged lightning storms causing rampant fires, destruction of buildings, etc. No fire trucks to come to the rescue (they run on electronics), random people in fields get zapped to death, and so forth.

Even if we could roll out new transformers and get the power grid back online in a reasonable time, a large enough CME that caused a world-wide lightning storm could be just about as little or as much damaging as you want it to be. I mean, CMEs could be large enough (in theory) to obliterate the world altogether, so your scale is everywhere from "no one noticed" to "world destruction" - you can scale the CME to however damaging you want it to be.

Answer 3

A sufficiently large volcano would (and has done, many times) have the result you're talking about.

A volcanic eruption in 1815 caused severe climatic and agricultural effects worldwide for more than a year. The eruption dumped tons of fine volcanic dust into the stratosphere that reduced sunlight and affected temperatures and rainfall across the globe. This resulted in crop failures, flooding, and all sorts of related disasters.

Anything VEI-7 or higher can generate global effects, and the closer to the equator the better, in terms of ensuring both northern and southern hemispheres are affected.

Likewise, a sufficiently large meteor impact would do it too. @Slarty's idea works if you want to spread small impacts all over the globe. One large impact would do the job too by the same mechanism as the volcanic eruption: by injecting megatons of dust into the atmosphere.

Answer 4

How about a meteor strike? Something a little smaller than the 11 to 81 kilometres that was the Chicxulub crater would still do immense worldwide damage.

Or how about a large volcanic eruption like Krakatoa? Depending where it happened, you could get direct and indirect effects such tsunamis.

Finally, there's always a Megatsunami, such as the canary islands collapsing.

And of course with all of these, assuming you hit a nuclear power, especially if you've upped the tensions in the area, you can trigger a limited nuclear strike (I'm assuming limited, as you wanted global nightmare, not global destruction).

Answer 5

Maybe a small Oort cloud object falls in towards the inner solar system and is disrupted by a close encounter with Jupiter on the way. The debris swing around Jupiter and are directed at Earth which is just at the wrong place at the wrong time. Hundreds of large rocky and icy objects impact across Earth, some burning up, some making relatively small craters but other making big impacts.

The amount of devastation could be dialled up to whatever you want depending on the size and nature of the object, the degree to which it disintegrates on approach and during atmospheric entry.

This could be started by any orbital disruption in the Oort cloud. Technically advanced humans might make matters worse in an attempt to deflect the object that goes wrong causing a shot gun effect. At least some major centres of population should be badly affected by being hit or near miss or affected by Tsunami.

Answer 6

Assuming that the defensive layers were built out from our world with each more distant layer adding to the security provided by the closer, earlier constructed layer, then the closest layer (the one which falls) would be the oldest layer. It would have been constructed at a time when the deity's influence on the planet was higher than it has subsequently been. The deity may have had more influence before the first layer went up, but subsequent layers would have been built from a comparably safer situation.

If that was the case, then the first layer may have been unsuccessfully attacked by the deity immediately after its construction but before the second layer went up. The energies or incarnations of that attack might have subsequently been trapped between that first layer and the rising second layer. Imagine the first two layers have risen, dividing the universe into three realms...

• Inside : where we are
• Outside : where the deity is

and

• Between : where the energies and incarnations of the deity's last attack have been trapped for millenia.

Subsequent defensive layers then arose between the second layer and the deity, at which point he accepted his loss, stopped making direct magical attacks and began working towards a more subtle, long term solution involving a cult and seven brides.

Now drop the first layer...

The energies and incarnations of the deity's final attack finally reach our world in the form of...

• Plagues : Viruses created by the deity using his transcendent understanding of biology.
• Pestilence : Snakes, locust, carrion beetles. The deity has a special affinity for vermin and can call them out in great numbers.
• Shadow : By enveloping the world in a sunlight diminishing cloud of space dust, the deity can cause crops to fail and initiate a decade long winter.
• Madness : Perhaps the trapped energies spread out across the planet as a telepathic wave, carrying madness inducing images to the minds of all but the most psychically deaf, shattering the sanity of many, inspiring murderous frenzy.
• Monstrous Minions : Perhaps some of the incarnations trapped between the layers were demons, the deity's foot soldiers; bulletproof, flying, shape-shifting, spell-casting abominations who can only be defeated by the magic which our ancestors forgot centuries ago.

The pocket between the first and second defensive layers is your candy jar! You can put anything you want inside.

Answer 7

As I interpret it, your deity comes from outside our universe - ie. outside our 4 dimensions of time and space, so he/she/it will burst in to existence in a sudden event that will cause a severe disturbance of the fabric of space-time, which can trigger events on a cosmological scale, so how about a nearby gamma ray burst? According to Wikipedia, "a typical burst releases as much energy in a few seconds as the Sun will in its entire 10-billion-year lifetime" - it might even be too violent, if your story needs survivors, but you can vary the distance, I suppose: the further away, the smaller the effect.