1. The greenhouse effect is useful. Without it we would all freeze to death on an earth with no atmosphere. Research has shown that the level of greenhouse gases in the air drop and rise as a natural cycle. However, human induced activities has made the amount of gg in the atmosphere rise to an natural amount. This is due to: cars, the industrial revolution in 19th century etc.
2. Water vapour, carbon dioxide, methane, nitrous oxide and ozone which occurs naturally. CO2 is the one which is currently the biggest concern as it is increasing the most.
3. Scientist melt ice containing bubbles of air from millions of years ago and compare it with today to see this is natural.
4. We cut down trees which photosynthesise and is the only process to remove CO2 from the air.
5. It is not always economically viable for the government to issue a clean air act which could help reduce problems. They are unwilling to spend money.
6. Global warming happens naturally as well as global cooling so scientists are not sure if it is us or not.
7. Yes there are. They say that our activities can't possibly be contributing to global warming that much, though it has been suggested that something like this caused extinction of dinosaurs years ago.
