Quoting BOAC:-
The climb is still unexplained.
Came across this article quoting an Airbus pilot at some length. It offers a (pretty hair-raising) explanation of what MAY have happened. Obviously there's no way I can 'authenticate' it - and I didn't try to delete the expletives!
- but I hope it's of interest.
An Airbus Captain’s Take on the Air France Disaster | Autopia | Wired.com