This post-apocalyptic environment, as narrated in the book, depicts a world where most if not all animal life has been abruptly killed, and similarly most vegetation burned out. After the disaster, the world is left full of ash and fog, and turned cold.
What kind of disaster can cause such an environment? I could think of some possible causes, like eruptions, or maybe a space object collision, or even nuclear warfare, but I'd like to get some scientific-based reasoning.
It sounds very much like the description of a Volcanic/Nuclear/Impact Winter.
They are all different ways of causing the same end result which is the injection of massive amounts of ash and dust into the upper atmosphere. This screens off the sun and causes global temperature to drop and plants to stop growing properly.
The result is massive famine and starvation, cold weather, and permanently overcast skies.
The different names depend on whether it is caused by a massive Volcanic Eruption, Nuclear Wars, or an Asteroid Impact. Each of those would have different other side effects:
Nuclear: There would be high levels of background radiation increasing mutations and miscarriages. Some areas would become dangerous to visit.
Asteroid: Depending on the location of the strike expect massive Tsunami's and Tidal Waves to sweep the world, the impact area itself would be obliterated and the resulting firestorm would cover a huge portion of the globe.
Volcanic: This would have the smallest immediate side effects (although expect a lot of poisonous gas, sulfur, lava flows, etc. It could also last the longest though since the dust from the other two options would start clearing after a few years while the volcanoes could keep erupting for far longer.
There's always the option of combined events as well, for example an asteroid impact on one side of the world could trigger a volcanic eruption at the other side once the shockwave reaches.
I don't even think you need a collision to screw things up royally. A near miss by a super massive object can do a lot of damage seeing as how our planet is tectonically active. I'd ask for more clarification on abruptly. I only mention it because I suppose you could get a disease or virus (dumb virus but hey they are all reproduction and no brains) that would affect the ability of animals to reproduce. Thereby you'd abruptly get a die off, but it would not be immediate. No to mention a disease of virus which only affected animals, humans might seek to cull all the animals.
If you want a quick extinction event, how about a Gamma Ray Burst from a nearby star?
While we are constantly bombarded with them, they are mostly from billions of light years away. But they are unfathomably intense - billions, trillions, quadrillions of times more energy than our Sun emits.
But what if... a nearby star went supernova and released one? In a worst case scenario, in seconds, every living thing on Earth would be dead. The Earth would be completely sterilized. But if it was less than worst case, pockets of life might survive. Virtually everything around you would be dead. A few lighting strikes later and you have massive forest fires. These fires cover the Earth in a thick blanket of smoke, blocking out the Sun and bringing about a long, cold winter. In fact, some have suggested such a burst caused one of Earth's actual mass extinction events.
But, I wouldn't lose any sleep over the idea of this actually happening. There's no stars near enough that could produce such a burst.
Well, that we know of.
Yellowstone Supervolcano erupts every some 600 KY. Last eruption ejected approximately 240 cubic miles (1,000 km3) of rock, dust and volcanic ash into the sky
