If the media and scientists and people in power all just said "well, there may be problem and I guess we should check it out" then no one would do anything. If instead you state "THE SEAS WILL RISE AND ENGULF US ALL AS WE COOK TO DEATH" then you might motivate some people to start thinking a little "greener". It may not be the truth, but the truth is never as motivating as the truth out of context.
People are trying, but with any kind of fear tactic you'll likely get opposition. Being "green" isn't cheap either, so of course that's a pretty big factor in why anyone would want to oppose it.
Scientists, unfortunately, are rarely capable of persuading the masses themselves. If the media was more inclined on helping out then it could be done, but unfortunately the media is too busy making mountains of money off of war stories to give much of a forget about something as bland as global warming. There will need to be a law reform before anything gets done at this point, and the US is probably going to burn before it accepts anything those kyoto guys have to offer as a solution.
Canada isn't faring too well either really.