9. How does climate change affect injection mold?

In higher humidity conditions, apart from the increase in water content in the air in the tool void prior to fill, maybe you're getting condensation at times (if the press is held-up between shots), in which case you will be pushing lots of water into the weld-line. Worth noting, also, is that even if you have the same barrel settings and water temperature and flow settings throughout the year, actual conditions that the material encounters (precise melt temperature at point of entry into the injection mold and actual mold surface temperatures) will vary, because of the R.H. and temperature differences. Hire a thermal imaging camera at relevant times and look at the readings on the parts at point of ejection. You'll see differences, I'm sure.
     There are possibilities to employ vacuum-assisted venting (by default, this would pull moisture out with the air) in the injection mold void prior to fill. Also, as I've seen with multi-impression PET preform molding, air-conditioning enclosures around machines.