When applied to an illness, chronic means persisting for a long time or constantly recurring. Often this is contrasted with acute which means an unpleasant or unwelcome situation or phenomenon present or experienced to a severe or intense degree.
Most are familiar with diseases that are acquired by humans, other animals or possibly lower life-forms, but what about more complex life-forms, like Earth’s environment. If we define Earth’s environment as a life-form, human-caused climate change is definitely a disease (then would we definitely be germs?).
Rather than bantering with definitions, we should be looking for a cure to this disease, but, of course, we already know what this cure is: stop emitting greenhouse gasses. However, this is easier said than done, but we really need to do it.