Arsthbt

I'm trying to think of a scientifically plausible reason for humanity to be forced to abandon earth that would leave animals and plants largely untouched. Is there any natural disaster that would have such an effect? If not, is it possible for humanity to develop a weapon that would unintentionally have this effect?

A super fungal infection could threaten most of humanity while leaving most species of plants and animals unharmed. A super fungus that developed a resistance to most fungicides, could wipe out most of the plant based food supply. Most of the world is dependent on staple foods like rice, corn, wheat, potatoes, and soybeans. If all the these crops where to die out, in a scenario similar to the movie Interstellar, then most of humanity is looking at starvation.

Another scenario in which the vast majority of cash crops die off is, if all of the bees die because of colony collapse disorder. Bees are one of the best pollinators and serve an important ecological niche. Growing anything becomes a lot harder without them.

A natural disaster that would have this effect is tricky to conceive - humans are still animals with the same fundamental biology and physiological requirements, and broadly speaking what affects us affects them and vice versa, for example toxins and radiation. I imagine that anything that would specifically require humans to abandon Earth but does not affect animals would almost certainly have to be artificial in nature, or at least origin, since it would very likely have to be targeted specifically at us.

One possibility that could potentially arise naturally is a virulent pathogen that specifically and exclusively attacks humans (and perhaps incidentally some of the great apes) - assuming the majority of organisms are unaffected by it, they could nevertheless be carriers for some time to come.

That said, depending on the nature of human civilisation at the the time of the event, leaving Earth (assuming you mean colonisation of other worlds) could be considered a drastic response - for example if it happened today, it might require huge infrastructure changes. An alternative that would be much easier to implement would be hermetically sealed habitats and the use of hazmat suits.

Most disease suffered by humanity does not affect any other creature

And the really cool thing about a plague that threatens to kill everybody if we don't get somebody off the planet (if the words "cool" and "plague" can be used in the same sentence without getting myself labeled a psychopath), is that you have to leave people behind. This gives you a nearly endless stream of sub-plot possibilities...

• Panicky infected people trying to get off the planet. (Denial)


• Offended infected people trying to stop you. (Jealousy)


• Do-gooders who think that leaving people behind to die is mean. (Misplaced compassion)


• The doctor who stays behind to cure the innocent. (Personal sacrifice)


• Etc.

Also good for a story is the fact that you have a wide array of "where did this start" scenarios to choose from.

• An ancient, rotting tree is pushed over by rainforest-destroying tractors, releasing the plague of a lifetime.


• Tony Stark was playing around with what he was sure was a great way to exacerbate hedonism but created the zombie apocalypse instead.


• The government was trying to pacify the population by putting G-23 Paxilon Hydrochlorate into Earth's air processors (you know, the ones we built to reduce pollution and reverse climate change).


• The wrong vulture was eaten by the wrong family in central Africa at the wrong time after it had eaten the wrong diseased, dead lion.

And the best part of it is, thanks to our wonderful immune system (including the blood-brain barrier), almost nothing that infects us will infect any other animal. Sicque illud

The great majority of humanity has been intentionally altered at some point in the past by some biological or technological process. This was originally done in order to enhance or improve human lives. However, an unforeseen event has turned that alteration on its head, which is now becoming lethal or highly incapacitating because of an interaction with the atmo/bio/technosphere.

Moderate levels of radiation would give you this (stick with me here).

Animals in general do not live into old age; they die young from predators, disease and stupidly minor accidents. As such a bit of radiation, while not great, isn't that high on the problems list.

On the other hand, humans dont like it when only half their children make it to adulthood and very few make it to old age. Worse still humans are long lived animals so have more time to be affected.

In fact as chernoble showed; this may actually be a net win for animals. The radiation drives off their main predator (humans) entirely, leaving to a nature reserve of sorts

http://www.bbc.co.uk/earth/story/20160421-the-chernobyl-exclusion-zone-is-arguably-a-nature-reserve

However, it's important that the level are "moderate" and perstist for a long time. The release of a radioactive element with a long half life would give you that

Is there a hypothetical scenario that would make Earth uninhabitable for humans, but not for (the majority of) other animals?

Only one, that's plausible, if other animals can survive so can people, especially with our proven ability to adjust our local environment to better suit us by using our "big brains".

So the only plausible scenario is almost certainly a violently virulent human disease able to survive in multiple other vectors besides humans without being deleterious to any other animals health, such a thing almost certainly has to be engineered rather than be a naturally evolved thing.

Nothing else plausibly fits the criteria you've supplied.