I dont think anyone really cares what the scientists predict. Its the tragedy of the commons, no one will really change their behaviour anyway, even when it becomes unbearable to live in many parts of the world.
You're talking in generalities. Even if it's not the majority of people, some people will change their lifestyles, or at least parts of it (buying eco friendly cars, using less AC, eating less meat, etc.) But in general, you're right, most people won't do enough. That's why there need to be institutional changes, like investments into green energy/tech and incentives for companies to pollute less.
It is worse than that, the incumbent politicians don't want to be seen as 'lefties', and there is a lot of people with money with a vested interest in burning more oil and coal. I think individuals changing behaviour is hopeless, but taxes that make doing the wrong thing expensive (and vice versa) is probably the only way, but politicians don't want to do that.