Backup stuff first.

  1. Download and install LiteLoader onto your 1.8 Optifine version (might have to show other versions) http://jenkins.liteloader.com/job/LiteLoaderInstaller%201.8/
  2. Download the first 405kb file from here and put it in your .minecraft/mods folder https://github.com/dags-/MAtmos/releases
  3. Open your launcher and change the environment to whichever one you installed LiteLoader into
  4. Run the game and press F7 to bring up its menu
    1. There will be a loading screen on launch if it works
  5. As an added option, you should follow these steps
    1. If you don't know how to do this, download this file http://www.distantlands.net/wiki/_media/msi_biome_atmosphere.rar
    2. Extract my edited file and find the msi_biome_atmosphere.json
    3. Open the msi resource pack you downloaded earlier (without extracting it) and find the msi_biome_atmosphere.json file
    4. Replace the one you just found with the one I edited