Ndtyhij

A universe-destroying parasite is set loose, and basically earth is placed under magical quarantine. (Think of it like the world is wrapped in magical cellophane.) My question is, how would earth's environment change, if at all, if the atmosphere is completely closed off from space? Would it affect pollution levels? Climate change? Plant Growth? If this does affect life, how long until the earth is no longer habitable?

Here's some more info: The forcefield is clear, so light can pass through it, though nothing else. It might absorb some heat energy, though, but not catastrophically. No substance can leave or enter through the field, not even on a molecular level.

If electromagnetic radiation can go unobstructed, there won't be any visible effect.

Earth's atmosphere is very stable, meaning it's not exchanging any material with the outer space (not in meaningful amounts). If Earth's atmosphere is locked in, everything will just go on without any noticeable effects.

On a long timescale (hundredth of millions to billions of years) the effect would become noticeable, because as the Earth would warm up, it is expected to lose water. However, with "magical cellophane", that won't happen, so the Earth as we know it would live on for a longer time. Also, asteroid impacts won't threaten Earth any longer.

Depending on how much heat it absorbs, it may exacerbate global warming. Absorbing heat is basically how greenhouse gases work. If your forcefield absorbs heat it will work just like a greenhouse gas. The effects of global warming are readily available via Google search so I won't go into more here.

I think what may be more interesting, is if it doesn't absorb heat. Depending on the altitude of this forcefield, its effects will vary.

First, lets assume the forcefield is high enough that only a negligible amount of atmosphere is outside the field. In real life, the atmosphere slowly loses its lightest constituents to space; Hydrogen and Helium especially. The forcefield will prevent this. Helium is continually produced naturally by radioactive decay of natural radioactive elements like Uranium. This means the amount of Helium in the atmosphere will slowly increase. Another effect is that the field will cause some limited heating. This is because the most likely atoms to be lost in real life are the most energetic, i.e. the hottest. If your forcefield stops them, they will stick around and stay warm. I would expect this to be much more minor than climate change in real life, but it's something to consider. Last, you will no longer have shooting stars. You might have a single tiny flash if your shield burns stuff up somehow, but not if it just deflects it.

If the forcefield is within the atmosphere, it gets trickier. The atmosphere above the forcefield will slowly be lost to space by the mechanism I explained above. It will also cause some minor global cooling, as the highest levels of the atmosphere is also the hottest. This won't change the atmospheric pressure inside the field though, because the field will hold it in. If the field is below atmospheric currents like the jet stream, the weather below will go crazy. Without currents like the jet stream to move heat around, hot areas will get hotter, cold areas will get colder. You will see much worse storms at the borders of these regions, and generally higher winds. It'll be bad, really bad. But at least you'll still get shooting stars.

On the bright side, I don't think any of the situations could sterilize the planet. The last one I mentioned could topple civilization, but if they have the magic to make the forcefield in the first place maybe they could find a way to get around that. But even that won't kill absolutely everything.