If the mesh is too dense then you quickly run out of computing resources.
If the mesh is too sparse then the predictions you get from running the model are worthless.
Not to mention the amazing variety of boundary conditions that have to be included... boundary conditions that are changing and moving around to boot like:
- Cloud cover
- Sea temps
- Sea emissions
- Plant cover
- Snow/ice cover
- Volcanic venting
.
.
.
- Human generated emissions
Animal Emissions, and not just cows!
you forgot butterfly wing flapping in Africa. it has to be accounted for too.