Hypothesis: A world with magic users is (unbeknownst to them) slowly dying because of magic usage
Question: What would be the underlying cause of this slow decay?
- The magic in this world is in some way respecting the law of conservation of energy. If energy is spent while using magic (performing telekinesis, pyrokinesis, you name it) it is taken from elsewhere (from within, the environment, certain objects, etc.)
- The magic users are oblivious to this fact which means that the 'slow decay' of the world should not be easily determined
The question is in some ways inspired by the old Dark Sun campaigns, where you had 'defiling' and 'preserving' magic. Defiling magic caused a slow decay of the world (in the sense that energy was taken from plants and life in general) and finally led to a Mad Max-like desert world that could barely sustain life. Obviously this is quite visible and its progression was clear to the world's inhabitants.
A different dynamic would be that magic users are merrily shooting their fireballs or constructing their earth golems, until they are confronted with thier plausible demise. Liken it to the effect fossile fuels have had on our world: fossile fuels certainly made our lives easier and allowed many scientific advancements, but at some point we figured out we can no longer continue like this for it might lead to catastrophic results for our 'habitat'. But in the interim we weren't aware of its harm.
Ideas I've had were drawing energy from the sun. However, it was justly pointed out that the sun cannot reasonably be depleted if you want the magic spent to have the same energy output as the energy input. It could also be sourced from the core of the planet, which might destabilize the planet's magnetic field and kill all the inhabitants due to the sun's radiation. Not sure if this theory could hold as I'm quite clearly not a scientist.