If you want to care more about distant victims, set aside your mental image of a large tragedy, focus your mind on one particular victim, and open your heart.  If you want to care less, instead of thinking about any one victim, try to visualize a much larger group of similar victims.  Now here’s the key question: do you want to care more or less?  Not sure? See which image you put in your mind, long enough to act on it.

Another interesting post from Overcoming Bias--which I've said many times is probably one of the best blogs on the Internet.