Carbon dioxide, the most significant global warming gas, is odourless, invisible, and an easy thing to ignore as our world heats up to dangerous levels. At Greenpeace, it's part of our job to make the invisible impossible to ignore. Often this means going to the source of the problem - hanging a banner on a coal plant's giant smokestack, for example. Other times, it means reminding decision makers they have a higher responsibility than the corporate bottom line.