Close, but pollution doesn't go away completely. In fact, that is completely and unequivocally far from the truth. Lets discuss: Oak trees emit Isoprene (in large quantities, esp in texas), Lightning produces NOx compounds, Volcanos produce more pollution in one eruption than the US does in an entire year. Volcanos and dust storms are huge producers of particulate matter. I hope you don't mean to tell me that when humans are gone that these things will magically disappear as well....
Funny story, Hydrogen costs more energy to produce than you get from combusting it, or using it in a fuel cell. Where does the energy come from to produce hydrogen? well, usually it comes from petroleum. A hydrogen economy is impractical. Do I have a solution to the energy problems we face, of course not. But unless you can magically mine hydrogen from space somewhere, then a hydrogen economy won't work. Energy has to come from somewhere, and last I checked hydrogen doesn't grow on trees. It is important to note, that ethanol can be made from trees though, an ethanol economy would be much more practical. Yes, it still takes energy to make methanol, but not even a measurable fraction of the energy it takes to produce hydrogen.
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Close, but pollution doesn't go away completely. In fact, that is completely and unequivocally far from the truth. Lets discuss: Oak trees emit Isoprene (in large quantities, esp in texas), Lightning produces NOx compounds, Volcanos produce more pollution in one eruption than the US does in an entire year. Volcanos and dust storms are huge producers of particulate matter. I hope you don't mean to tell me that when humans are gone that these things will magically disappear as well....
Funny story, Hydrogen costs more energy to produce than you get from combusting it, or using it in a fuel cell. Where does the energy come from to produce hydrogen? well, usually it comes from petroleum. A hydrogen economy is impractical. Do I have a solution to the energy problems we face, of course not. But unless you can magically mine hydrogen from space somewhere, then a hydrogen economy won't work. Energy has to come from somewhere, and last I checked hydrogen doesn't grow on trees. It is important to note, that ethanol can be made from trees though, an ethanol economy would be much more practical. Yes, it still takes energy to make methanol, but not even a measurable fraction of the energy it takes to produce hydrogen.