evidence: - Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor. [...] Water vapor is the most abundant greenhouse gas, but because the warming ocean increases the amount of it in our atmosphere, it is not a direct cause of climate change. Credit: John Fowler on UnsplashFEEDBACKS: A process where something is either amplified or reduced as time goes on, such as water vapor increasing as Earth warms leading to even more warming.