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This question already has an answer here:

I am writing a post apocalyptic story in which a large amount of the foliage is dead and agriculture has become much more difficult. My original idea was to say that this was caused by an ancient nuclear war or climate change, but these have both been done a million times.

Are there other possible ways that humans could inadvertently or purposefully cause major disruption of the food chain? One idea I had was blocking out the sun as in the Matrix, but what would cause this/why would someone do this?

This could be one major cataclysmic event or a gradual change in the environment over the course of thousands of years.

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marked as duplicate by Aify, EveryBitHelps, Renan, Frostfyre, nzaman Apr 10 '18 at 12:26

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ What tech level? $\endgroup$ – HopelessN00b Apr 10 '18 at 6:38
  • $\begingroup$ @HopelessN00b I suppose any technology at or above the technology we have now, but before we are able to have major civilizations on other planets. $\endgroup$ – William Oliver Apr 10 '18 at 6:42
  • $\begingroup$ Definitely related, possible duplicate: How would humanity enter a Dark Age? (Full disclosure: The accepted answer is my own.) See also the many questions in the "linked" sidebar to that question. $\endgroup$ – a CVn Apr 10 '18 at 9:36
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    $\begingroup$ As currently phrased, is this not opinion-based? How would you judge a good answer? $\endgroup$ – EveryBitHelps Apr 10 '18 at 10:36
  • $\begingroup$ A 1930s(?) SF novel I once read, IIRC titled "Nordenholt's million", had a lightning strike mutate a denitrifying bacterium which ran out of control across the world, removing all nitrates from the soil in all but a few naturally protected sites, and destroying all plant life. Cue unexpected apocalypse. The book had fascistic overtones and an "oldfashioned" attitude to cardboard female characters. It was also so much embrittled (ancient paperback) that it fell apart into small fragments as I read it. Anyway, you might recycle the underlying idea. Sorry, I cannot recall the author. $\endgroup$ – nigel222 Apr 10 '18 at 10:45

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Pollution of water. Majority of the world's photosynthesis is done by algae.link here

There is less oxygen, chemicals and micro particles in the air. Sealife is almost gone and the surviving fishes are dying from the plastic micro particles from degradation of plastic. Whales are dead.

Nature could fix this, since having less photosynthesis means there will be more CO2 to process, so more algae would grow back once the chemicals will stop killing the algae.

You could add some toxic or acidic rains to get the calamity inland. (The chemicals are evaporating along with water)

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  • $\begingroup$ Genetically optimised algae can be released to improve CO2 process. After this monoculture replaces all competition, some malady decimates it. More than that, if it's a virus it doesn't just disappear so algae can't simply regrow: it keeps being destroyed by ongoing epidemic. $\endgroup$ – Daerdemandt Apr 10 '18 at 9:08
  • $\begingroup$ It would be impossible to completely replace the competition. But it would be a nice plot twist if the chemicals were actually something that was supposed to stop the algae disease. $\endgroup$ – Nuloen The Seeker Apr 10 '18 at 9:23
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One possibility that hasn't been explored all that much is Volcanism. Volcanoes are one of the world's largest producers of greenhouse gases, and they produce more of these than man does with industrialisation. This is one of the primary arguments of climate change skeptics, although a discussion of this issue is outside the scope of your question and therefore won't be undertaken here.

My thoughts on this though are that if you had a new mining technology that allowed you to extract minerals from the crust at deeper and deeper levels (or you simply need to do that as you're depleting minerals near the surface at a faster rate) then it's possible that you could destabilise the crust.

The Mantle (the large section of the earth between the core and the crust) is very hot, molten rock and other minerals that also seems to be under quite a deal of pressure under the surface of the crust. If you dig enough holes that are deep enough, you can weaken the crust to a point where you can encourage more volcanoes to erupt out of mine shafts.

I should state that this is not likely to happen with modern mining tech, but a near future state may make something like this possible. If we're not careful in such a scenario, we could punch through the crust just a little too far and generate our own volcanoes.

This could cause massive greenhouse based climate change on earth. It would be pretty destructive for humankind especially, but agriculture would also be affected quite substantially, at least in the short and medium term (geologically speaking).

The good news is that igneous rock eventually breaks down into very mineral rich soil, actually improving agriculture in those areas. This is in part why there are so many settlements near volcanoes in the modern world. So in time, if mankind can get through the intervening periods, plant life would likely thrive after such a cataclysm. Of course, your real problem in that case would be diversity as many different species of food plants would be hard to come by.

It should also be pointed out that such mass volcanism would also have an immediate side effect for human civilisation; it would immediately (and more or less permanently for the current generation) ground all aircraft as the volcanic ash in the air literally destroys aircraft engines in flight. This would make the trading of any existing plant seeds and varieties even more problematic.

Of course, humans would have a harder time surviving this scenario than plants would. The only saving grace would be that most mines are not around highly populated areas meaning that at least you wouldn't lose too many cities to magma flows. That said, there would be immediate food production concerns in many countries, and given that all global transport would be limited to surface based, this could cause the kind of global apocalypse you're looking for through pure starvation.

Of course, after the first few 'artificial' volcanoes erupt, you'd hope we'd stop drilling deeper holes, but then sometimes we as a species are just not that bright.

Ideally, you'd want to be living in a poorly mineral resourced country with plenty of high ground in some form of farming village if you want to survive this. That of course also limits your availability to tech, but that's a matter for your story world rather than the kind of apocalypse that has caused the world being set.

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  • $\begingroup$ There's also the idea that CO2 storage technologies that pump the gas underground could trigger tectonic activities such as eruptions and earthquakes. Doesn't have to be mining. $\endgroup$ – HopelessN00b Apr 10 '18 at 6:37
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    $\begingroup$ CO2 emission from volcanic eruptions is less than 1% of the rate from fossil fuel burning. $\endgroup$ – Oscar Bravo Apr 10 '18 at 7:08
  • $\begingroup$ I read that NASA was considering to drill a hole to release heat and pressure of the yellowstone super volcano... What if that goes terribly wrong!? :D $\endgroup$ – Totumus Maximus Apr 10 '18 at 7:29
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A new "miracle pesticide" that's completely non-toxic to humans is invented, and is quickly adopted worldwide. Unfortunately, as it accumulates in the soil it slowly starts to interfere with the nitrogen cycle - with the plants unable to absorb nitrogen, they start to die out.

This wouldn't be quite so bad if not for the fact that the reason it happened so slowly was because the chemical leeches through the groundwater into rivers/ponds/oceans, evaporates with the water, and comes down in the rain - meaning that everywhere is affected, not just the locations where this pesticide was used. {EDIT} As a pesticide, this also kills all of the pollenating insects world-wide, hastening the floral demise. On the plus side, no more mosquitos.

Plants fall, everyone dies.

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  • An antibiotic-resistant super-flu (or super-ebola) pandemic.
  • A plastic-eating bug, either deliberately developed as a biowar germ or natually developed in some landfill and then spread.
  • A hack of a very widespread IoT device kills the internet. A few hours after the food supply chain breaks down, humans almost everywhere riot and thus prevent any orderly restart. It goes downhill from there.
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    $\begingroup$ The plastic-eating bug could also have been developed on purpose, out of environmental considerations. But there are many kinds of plastics... it would be like imagining a virus that attacks all animals indiscriminately. $\endgroup$ – T. Verron Apr 10 '18 at 6:27
  • $\begingroup$ How can a plastic eating bug lead to an apocalyptic scenario? $\endgroup$ – Nuloen The Seeker Apr 10 '18 at 7:01
  • $\begingroup$ @NuloenTheSeeker spare a thought about the amount of plastics used in our lives today. Eliminating or even threatening them can easily drag civilization back with decades if not centuries in development. $\endgroup$ – Katamori Apr 10 '18 at 7:40
  • $\begingroup$ But surely the plastics wouldn't just disappear, the worms could be a nuisance and a new pest, but causing an apocalypse is way over the top. If anything these worms would be blessing to our current situation, because we have whole islands of plastics flowing in our oceans. $\endgroup$ – Nuloen The Seeker Apr 10 '18 at 8:07
  • $\begingroup$ @Katamori: few plastic items cannot be substituted by equivalent items in other material, the use of plastic is basically only an economic question. Too little to cause the post apocalyptic the OP described $\endgroup$ – Gianluca Apr 10 '18 at 8:12
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Destruction of the nitrogen cycle.

Nitrogen is essential for plants and animals, but it is fairly unreactive, making it hard to use in nature. Through fertilizers and pollution mankind is putting out enormous amounts of reactive nitrogen which can be used extremely easily by plants. One way we can see this changing the environment now is in increasing fertility throughout most of the world.

"In the Netherlands, for example, extreme reactive nitrogen levels have changed the Dutch countryside’s characteristic heathlands to grasslands."

This doesn't sound too bad, but when this reactive nitrogen hits the oceans it is disastrous. The influx of phosphors and nitrogen causes algae blooms, which choke out most other life in the area. This has caused dead zones along the Gulf Coast and other areas that stretch for hundreds of square miles. If this goes on the most productive parts of the oceans will be algae filled muck.

In their summary of water quality impacts of fertilizers, FAO/ECE (1991) cited the following problems:

· Fertilization of surface waters (eutrophication) results in, for example, explosive growth of algae which causes disruptive changes to the biological equilibrium [including fish kills]. This is true both for inland waters (ditches, river, lakes) and coastal waters. · Groundwater is being polluted mainly by nitrates. In all countries groundwater is an important source of drinking water. In several areas the groundwater is polluted to an extent that it is no longer fit to be used as drinking water according to present standards.

Also plants can only absorb a limited amount of nitrates. Once they take their maximum limit the remaining nitrate doesn't remain in the topsoil.

As with water and air, reactive nitrogen builds up in soil. There’s a limit, however, to how much nitrogen plants can use. When soil reaches a point at which plants can’t use additional nitrogen, it’s said to be “saturated.” And saturated soil, in theory at least, will shed any additional nitrogen introduced to it. But that nitrogen doesn’t leave unaccompanied. “When it leaches out of the system,” says Townsend, “it takes other nutrients with it, so it ends up acidifying the soil, and it takes things like magnesium and calcium out into the water. And you end up with a very unbalanced system.”

Another problem is that reactive nitrogen causes a whole cascade of problems in the atmosphere.

But as nitrogen levels continue to rise, Townsend says, the net health effects become increasingly negative. Furthermore, says Galloway, reactive nitrogen can not only impact many different ecosystems, but a single atom also can make mischief repeatedly, unlike most better recognized pollutants. “If you put a molecule of NOx in the atmosphere from fossil fuel combustion or a molecule of ammonium on an agricultural field as a fertilizer,” he explains, “you have a whole series, or cascade, of effects that goes from acid rain to particle formation in the atmosphere, decreasing visibility and causing impacts on human health, acid rain, soil and stream acidification, coastal eutrophication, decreasing biodiversity, human health issues in groundwater, and nitrous oxide [N2O] emissions to the atmosphere, which impact the greenhouse effect and stratospheric ozone.”

Even better, nitrogen damages the ozone layer at lower levels, and in the stratosphere it destroys the ozone layer. So on top of acid rain, increasing acidity in the soil and water, a cloudier sky and algae blooms, UV rays will be killing plants and animals.

So while it is a greenhouse gas, and far worse than CO2, changing the climate a degree or two is the least of the problems of an out of control nitrogen cycle. The earth will survive, but the food chain will be in tatters, plants will have to deal with intense UV rays, acidic soil and water, and agriculture will be very difficult but not impossible.

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A malfunction in a solar shield, launched into space to filter some sunlight and thus lessen global warming, has left half the world permanently in the dark.

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  • $\begingroup$ Basically the plot of Highlander II: The Quickening. ;-) $\endgroup$ – Gianluca Apr 10 '18 at 8:14
  • $\begingroup$ Or Snowpiercer. There are a million ways history can happen from that first incident. $\endgroup$ – Carlos Arturo Serrano Apr 10 '18 at 15:17
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Paolo Bacigalupi came up with an interesting one petroleum shortages combines with widespread access to advanced bioengineering results in large scale ecological and technological collapse from poorly regulated genetically modified organisms. Including genetically modified humans, super crops and designer toy species, (for instance cat have been driven extinct by designer cheshire cats) make it your own by choosing your own species and designs.

An easy one would be something that drives bees extinct, as a huge number of our crops , as well as a large number of plant species period,rely on bees for pollination.

Another option is a genetically engineered plague released by a terrorist group, kill enough of the population and civilization will collapse on its own. Make it an extremist animal rights group for fun irony.

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Depends on what tech level we're talking about, but to go a little near future, I'd suggest an asteroid mining accident. Some large, near-Earth asteroid is being exploited for the burgeoning space industry, and an industrial accident alters its trajectory just enough to make it hit the Earth with an extinction-level (or near-extinction level event), so we do to ourselves what nature did to the dinosaurs a while back.

Since you clarified that we're talking about before we colonize other planets, it should be easier to arrange the accident (or "accident") - space mining would probably still be focused around Earth orbit, the most efficient way being to drag the asteroids into a high Earth orbit of some kind. Someone makes a minor miscalculation, a thruster malfunctions, or even a malicious actor does it on purpose, and we get an extinction-level event instead of a source of minerals near Earth orbit. As an added bonus, without lots of inter-solar-system traffic, it's much more plausible that there's no way to stop or redirect our impending doom.

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Collapse of the phosphorus cycle in the biosphere - all phosphates are leached out into the ocean while mineral sources are long since used up. Plant life is increasingly stunted with no way of getting phosphates to the fields in a large-scale way. See https://en.wikipedia.org/wiki/Phosphorus_cycle

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Automatic war machines gone mad:

Nobody remembers who won the war, but the automatic, solar (fusion?) powered drones still wander the skies.

The ones with missiles and bombs stopped working ages ago, but the ones designed to fight the biological war still wander on, filling their deadly poison reservoirs from somewhere (or synthesizing material from the sea with nanobots or whatever).

Last vestiges of humanity defend themselves with whatever old AA-guns/-missiles they have left.

A huge plant and/or insect poisoning storage facility might wait somewhere across the mountains for destruction and salvation of the local populace...

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Over-population. This would create a demand for extra housing while, at the same time, creating an increased demand for food, putting more pressure on agriculture.

Both housing and agriculture would increase the demand for land, competing with each other to secure and use it. Natural resources would decrease as a result and the need to increase food production would industrialise and intensify the process, more pesticides, more genetic modification.

Natural pests become more resistant to pesticides, but cultivated strains of plants become modified to become increasingly toxic, the toxicity being removed by subsequent processing to turn into safe edible food.

Toxic plants, however, cannot be contained and are soon growing wild, out-competing natural varieties (which will be more palatable to wildlife) decimating the ecology. The bees somehow survive, but their honey is toxic to anything else. The cultivated land is toxic to anything but the genetically modified crops.

Result, a fractured food chain.

Maybe rats breed prolifically enough and fast enough to withstand a high mortality rate while evolving as necessary, but higher mammals cannot. The rats compete with man for available food resources.

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Cut food chains (probably combined with food shortage)

People are terribly efficient on destroying other species. Some deliberately, some through a pollution (and I don't mean just a literal waste, but also light pollution, radio pollution and sound pollution all affecting other animals and changing their behaviour to the level that might cause a speciocide). We're already facing a problems of decreasing number of bees that is probably going to cause a serious drop in available food.

Of course people will eventually find a way to replace it with technology but it goes far slower than the extinction of species. If this accumulates on more species and add increased number of people and reduced natural inhabitable environments for other species we might end up in a situation of a very severe food shortage with most sources of food extinct or polluted. Combine that with the problem that most food production ways are water inefficient causes this resource to become scarce and you have a nice apocalypse.

The worst thing is we might be actually heading in this direction somewhat undernoticed.

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One of the largest problems in the world is Climate Change and environmental impacts, what if the problems became too bad for our world and a group of scientists decided to genetically engineer a bacteria that would rid the world of fossil fuels by breaking them down chemically. This could also go into multiple variations, as in you could do an economic meltdown thus the food distribution is down, chaos would take over as electricity in various countries becomes the new gold or a war on the few remaining fossil fuels left.

After an amount of years the bacteria starts to mutate and starts breaking down more materials not just fossil fuels. As fossil fuels are carbon based, as well as most things in this world, it will start with plants and insects and keep going on from there.

This is just an idea. Thanks for reading.

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The Carrington Event was a coronal mass ejection that hit the Earth. If it happened today it could cause significant damage to electricity distribution systems. Without electricity our civilization is dead in the water, and much of the equipment required to build replacements is also dependent on electricity. For ideas about the immediate aftermath you might like to watch Episode 1 of "Connections" by James Burke (BTW, note where he is standing and the flight number he mentions. Spooky!).

Of course this is not an original idea, and the people who look after our electricity systems have put some thought into what to do about it. But there is no way to test those plans...

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  • $\begingroup$ Well - there is one way to test them but I hope we don't have to. $\endgroup$ – Alchymist Apr 10 '18 at 15:12
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Accidental explosions something of the sort near major fault zones such as Yellowstone would definitely cause some bad scenarios at least around some parts of the world.

An aerial chemical spraying malfunction could cause a lot of death to flora and fauna.

Overpopulation is a more gradual problem that, if left unsolved, could cause revolutions, wars (not necessarily nuclear, but still devastating), and food shortages and the destruction of much of the landscape to try to make way for farming. If there was a year of drought during this period then many people may die of starvation and be unable to tend to remaining crops and much of the earth's surface that had been cleared for farming would turn into a wasteland. Just a thought.

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The absolute worst-case runaway global warming, leading to a re-run of the Permian mass extinction. The (non-fictional, if somewhat speculative) book that you need to read about this is titled "Under a Green Sky", or Google that phrase.

If this is the case, it is not going to end well for the human race or for most other species. However, the time-scale on which it would unfold is long compared to a single human lifetime (though very short by geological standards). There will be a window during which life remains possible.

You will have to choose whether the characters in your story know that they are living in the end times for the human race with no possibility of reprieve, or allow them ignorant hope that things may get better for their children while dropping a bombshell on your readers.

(Yes I know you said you don't want global warming, but I don't think I have seen this worst-case scenario explored in fiction, where the atmosphere is turning toxic and the oceans will soon be ringed with dying fish trying to breathe the air because the water is even worse. Too gloomy? )

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First, a mutation allows crabgrass or a similar infestant to spread with even more abandon, threatening not only gardens but crops as well.

Second, a very specific catalytic herbicide is synthesized in ever-growing amounts to keep the infestant under control. Being catalytic and long-lived, a small dose will defend an area for a very long time.

And finally Nature's sleight of hand - the molecule at the heart of the herbicide turns out to be a disappearing polymorph. Almost overnight, the specificity of the herbicide turns into a curse for every kind of grass and most other vegetables, and plants start to die (not unlike John Christopher's Death of Grass). What plants succeed in adapting don't fare too well, and that's the scenario you described.

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