Carbon dioxide, the most important man-made greenhouse gas, gets most of the attention in efforts to stem the effects of climate change. While methane is considered a much more potent greenhouse gas, it breaks down into carbon dioxide and water in the atmosphere within 12 years or so. Carbon dioxide, the most important man-made greenhouse gas, gets most of the attention in efforts to stem the effects of climate change. While methane is considered a much more potent greenhouse gas, it breaks down into carbon dioxide and water in the atmosphere within 12 years or so. Environment Phys.org – latest science and technology news stories