Global climate change has the greatest potential to increase infectious disease incidence by acting on the of infectious disease.

spreading

Explanation:

The infectious diseases are very dangerous for the human population, as they can cause a pandemic very quickly, with thousands or even millions of people being affected by it. These type of diseases though tend to be concentrated in the tropical regions of the world, thus they are regional and can not have a global effect. If the temperature rises on global level though, than the situation will escalate for sure, as the viruses and the animals that carry them will be able to move toward the mid-latitudes, where the majority of the global population lives. That will mean that these diseases will spread out over much larger area, and they will have billions of hosts for it, while the human population will most probably end up with heavy losses from it.