There are many science studies that once you become a prisoner, instead of actually improving yourself, you degrade to the point that you become better criminal.
The world goes to reducing punishments and this is the way to go. Usually there is a "healthy" amount of criminals in every nation, but you will never solve the problem by increasing the sentences, this actually makes it worse.
The major reasons for success of Scandinavian countries in crime and punishment are larger than a single metric, IMHO. They have a (more) comprehensive philosophy that touches on many areas, all of which work together.
If the US adopted the prison conditions and lighter sentencing of Norway without other measures, it would be a complete disaster. For the US to get similar benefits we would need to (ideally) first shift our attitude toward thinking of criminals as people, and thinking most of what benefits society rather than how to punish for punishment's sake.