Chemically speaking, carbro and carbon are very different. Carbon transfer is an ultraviolet light sensitive process. The UV light reacts with a traditional sensitizer (potassium or ammonium dichromate), or with a "modern" sensitizer like we're discussing here, causes the gelatin to harden in proportion to how much light it received in order to trap pigment in the gelatin. You wash off the remainder in hot water, and are left with an image.

Carbro is a purely chemical process. It uses a very different sensitizer, which, when the sensitized carbon tissue is brought into contact with a conventional silver gelatin print, reacts with the silver and causes the gelatin in the carbon tissue to harden. The more silver (darker areas on the print), the more hardening of the carbon tissue.

There it is in one paragraph each.

William Crawford, "The Keepers of Light"
Richard Farber, "Historic Photographic Processes"
Sandy King, "The Book of Carbon and Carbro"

These 3 all have decent descriptions of the similarities and differences between the 2 processes. The first 2 are out of print, AFAIK, and the 3rd is self-published. Some google searching might yield some hits, too.

To others on this thread...I don't own any of Nadeau's books. Does he address carbro at all?

Hope that helps...