A plugin that adds four main aspects of climate change into the game (more may be added later, however I am making a mod for this same thing right now and I may not update this plugin). The features are:

• Greenhouse gases.
• Ocean acidification.
• Marine life dying due to ocean acidification.
• Extreme weather conditions (currently, this is just more storms).

Features that I might add:

• Localizing more extreme storms to a few biomes.
• More severe wildfires (also localized to a few biomes).
• Rising sea level.

I will probably link the mod version of this here once I release the first working version of it.
Note: To start running the plugin in your minecraft world, do /runccm