All of the disease types in Plague Inc. can adapt to their environment to improve their infectivity in different countries, but what about a plague that works the other way around, altering the local environment to create ideal conditions? Such a plague could cause such drastic climate change that it would trigger natural disasters, changing the world irrevocably.

Some possible ways this might happen follow:

- CO2 production. The host begins to exhale excessive amounts of carbon dioxide, creating a greenhouse effect and increasing global temperatures.

- Water absorption. The plague and its host absorb large amounts of moisture from their surroundings, making the environment increasingly arid.

- Mass lethargy. Hosts exhale a gas with a mild depressive effect, causing widespread lethargy and apathy. Work output drops dramatically and the global economy suffers. Cure research is also slowed.

- CO2 respiration. Host physiology adapts to use carbon dioxide instead of oxygen, but is highly inefficient, resulting in excessive use of CO2. The greenhouse effect is reversed and global temperatures drop.

I am not a skilled modder or particularly knowledgable about diseases, so I would very much like it if someone else were to develope this idea further.