Fixing nitrogen so we can't breathe it? We don't breathe nitrogen, except in the sense that it comes in our lungs and goes out unchanged.
Umm... Yes we DO breathe it, in a sense that its presence or absence in the air that we breathe are detrimental to our health.
Pump more of it in the atmosphere we breathe, changing pressure, we get drunk on it.
Pump it out of the atmosphere, bind it into ground, and we poison ourselves with the remaining oxygen or CO and CO2 - as both the air pressure and concentration of gasses in the air now changes completely.
Nor is there any sign that anybody's having problems breathing on Earth (except with the dust).
You have issues with being able to movie too?
It is a future problem, which would eliminate most air breathing life and most certainly all humans on the planet - IN THEIR FUTURE, AFTER THEY FIRST RUN OUT OF PLANTS.
Not then and there. Maybe not for the next 100 or 1000 years for the whole thing to play out completely. But it is a done deal.
Earth is ALREADY a dead planet.
Even "recycling" people for food will not help.
Again... same way that the REAL horror of "Soylent Green" is NOT "it's made of people".
It's that there is no more plankton in the oceans, while the individual trees and vegetation are viewed as prized statues.
That is why the only solution is LEAVING. Not finding more corn that WILL grow.
The idea of a blight that methodically wipes out one crop after another need some serious explanations.
It does not wipe out crops one after another. It has wiped them all out already.
Scientists have managed to keep creating a more resistant crop, one after another.
And they've run out of crops and (per)mutations. And that WAS explained.
Explaining the exact way the blight works is NOT needed no more than it would be needed to explain the existence of robots. Or cryogenics.
But it is REALLY easy to explain. And bog down the movie with EVEN MORE technobabble.
But if you really need a plot device spelled out for you... and don't want to accept that someone is producing electricity in their world without any power-plants being shown... and you simply refuse to imagine them somewhere beyond the horizon...
Plants ingest the nitrates thanks to nitrogen binding BACTERIA. Some of them symbiotic.
Just have them mutate so that they no longer bind nitrogen in the form digestible by plants, while still sucking the sugar out of the plants.
Or have them start feeding on the plants themselves.
Say we get a bright idea to create vitamin B3 (C6H6N2O) reinforced crops that will at the same time suck out the CO2 from the atmosphere AND create fertilizer (NH3), by creating a mutation of existing nitrogenase equiped bacteria.
Aaaand... we fuck it up.
Bacteria starts eating the plants from the roots up (getting their C there instead of from the atmosphere) and filling the ground with nicotinamide which then gets flushed away by water.
That's just one possible technobabble solution. From the top of the head. Probably requiring a lot of improbable science to work.
But it does not matter any more than the explanation (and the lack there of) of ANY other world-building plot point.
Why are there no MRIs? What EXACTLY do cars run on? What about the rest of the world? What's going on in Australia? Did Madagascar close its ports on time?
Story is NOT about intricacies of microbiology and technobabble. It's about SPACE. And exploration thereof.
Did anybody mention a large war? If so, I missed it.
Robots are former marines. NASA refused to drop bombs on starving people and was shut down because of it.
"Marines don't exist anymore". Or scientists. Or engineers. ON THE PLANET.
Entire planet is agrarian just to produce enough food.
Which is "not so bad". People used to "be too busy fighting over food to play baseball."
"6 billion people" is some distant, incredible, number from back when grandpa was a boy and there was magic everywhere.
It is hinted at huge, global, food riots in the past.
Big enough to warrant the government to ask NASA to bomb the civilian population.
Governments have nukes. Why call NASA?
Unless they want to bomb people with kinetic projectiles as nukes are useless if you want to plant food on the bombarded ground.
That's a war.
Between countries. On "too many people". Between starving people, over food...
The exact flavor and number and exact size(s) of the conflict(s) does not matter. Everyone LOST.
What matters is that the people and their technology level has suffered.
AGAIN... Story is NOT ABOUT THAT.
There was, indeed, time travel going on. Main character manipulated the books in a way daughter noticed said "stop" at an earlier time.
Not time travel. Nor a temporal paradox.
The whole point of the wormhole to the other galaxy and allowing for humans to come up with the solution on their own instead of just sending them the blueprints on how to build the spaceships and sidestep gravity - is in NOT violating causality.
Cause that IS NOT POSSIBLE.
It ends up being inter-universe travel.
And that would be of no use to humans of the future, Cooper or the humans of his present.
He would end up sending (possibly wrong) data to a daughter of some other Cooper.
Instead, they "borrow a cow" by creating a tesseract alongside of the 4th dimension of the back of the shelf.
They can create wormholes and grab people and robots dropped into black holes.
Either folding a piece of the universe into a 3-dimensional space along its 4th dimension, or creating a bubble-universe for the same purpose is probably within their reach.
Cooper is thus not communicating from the future - but from a temporary time-space outside of the universe.
He's outside time, not forward in time.
Telegraphing "S-T-A-Y" is him repeating to his past self the same exact words his past self already heard in the past.
AND it is something his daughter was saying, and would be saying, ANYWAY.
No information gets added to or removed from the universe, nor is there any alteration of the timeline, by the movement of information or objects along it.
There is no paradox and there is no time travel.
It's a loophole that allows them to tell the story about wormholes and all the other stuff without violation to the science as we know it.
Which works because... deus ex machina from the future.
But that IS the SETUP of the story.
The deus ex machina is OUTSIDE of the story, in a form of a "What if..."
"People from the future" don't land with their spaceships or appear like Q from the thin air, snapping their fingers - they set up the events long before (or after... or outside... they move outside the time) the events observed.
No deus ex machina lands on the stage - but one WAS used to construct the stage.
It has to be. It's science FICTION.
There is always a hidden deus ex machina in ANY fiction.