Personally I prefer PCP to CO2, due to performance differences, but can't afford a bunch of PCP rifles. Anyone worried about CO2 emissions should be planting trees, since plants breathe in CO2 and breathe out O2. Deforestation is the main reason for an increase in CO2. As a hunter, I have a vested interest in reforestation efforts. That, and I just don't like friggin' overdevelopment. I want to live somewhere without any neighbors, where I can hunt and fish all I want.