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Does he discuss this in the course? I haven't gotten that far yet but I look forward to it. I don't think anything different would happen, perhaps more thunderstorms for a while until the present equilibrium is reached. The earth plus its atmosphere is neutral in charge. There are forces occurring in the atmosphere that cause a separation of charges in the air -- thunderstorms cause negative charges to accumulate close to the earth's surface and +ve charges to occur higher up. Solar wind causes a distribution of charges too but I don't know a lot about atmospheric science. Friction between air and falling raindrops can also cause drops to carry charge. The steady state is a negative charge on Earth and a positive charge in the atmosphere, and because air is not a perfect insulator, there is a current that flows from the atmosphere to the entire surface of the earth all the time. Thunderstorms are the engine that maintain the average steady state charge separation. The 'clear-day' current causes -ve charges from the earth's surface to transfer to the +ve atmosphere but thunderstorms put -ve charges back to the earth, restoring the steady state. So to answer your question, given a net neutral charge of the Earth and atmosphere, if the earth were suddenly more positively charged for whatever reason, more lightning strikes would occur until it again became -vely charged, owing to a stable steady state reached by the various forces acting on the atmosphere to generate the current charge separation.