Buy a pack of cigarettes, and a printed warning from the surgeon general will remind you that smoking causes cancer.
Obviously, you've chosen to smoke anyway. But perhaps one day you'll look at that message, printed on the pack, and resolve to change your ways.
Now, apply that idea to global warming.
A group of Bay Area environmentalists wants to slap warning stickers on gasoline pumps, telling drivers that the fuel they're buying is cooking the planet. The stickers would constantly remind consumers of the link between driving and climate change.