1. Perhaps, but it would not mean the same thing. Uncaring is bit more specific than Indifferent.
One can be indifferent, meaning that that one hasn't arrived at any particular reaction, and maybe won't, but maybe will: that is not necessarily uncaring, it is just that one doesn't consider the subject to be something worthy of making a decision about.
One can be uncaring, meaning that one HAS arrived at a particular reaction, which is that one doesn't care about what happens about the subject.
2. No. Indifferent here means that they do not consider it necessary to have an opinion about whether they should care about the environment or not. Uncaring means that they have made a positive decision not to be bothered to care for the environment.
3. Not interested is one stage back from indifferent. Not interested means that the subject doesn't spend any time in one's brain, so one hasn't even thought about whether to make a decision on it. One can not be indifferent about something one hasn't even bothered to think about!