Would a heat pump be a good idea for my home? How would it impact global warming?

A technical friend recently pointed out that last year, 4 million heat pumps were installed in the US, up from 1.7 million in 2012.  I am relatively unfamiliar with the technology, but it does inspire a number of questions.
  1. Would a heat pump be a good idea for my home? 
  2. Would it use less energy than my current heating and AC?
  3. How would it impact my utility bills?
  4. How would it impact global warming?