This can (and has been) modeled using future value analysis (from economics). Since future payments are discounted (based on interest and inflation), extending copyright means that the value now of creating a new work increases but by smaller and smaller amounts. Somewhere in the 15-30 year range is about "right" according to most studies -- the additional value of even an infinite extension is minimal at this point.
Then there's the economic value of a work: very few copyrighted works have an economic life of one year, let alone a century. This is particularly true since copyright protections were extended to all works rather than just those which were registered with a copyright office (this post is copyrighted, however my economic interest in it is nil, still, it will extend for the next 120 years).
The real argument for extensions is copyright term in works of enduring value whose copyright is about to expire. This is the "Mickey Mouse Copyright Law" in the US. Walt Disney's first Mickey Mouse cartoon, "Steamboat Willie" (itself borrowing very heavily from earlier works) was published in 1928, and there's been a strong trend in extension to prevent works from at least this date from ever entering the public domain.
This results in the exceptionally strong protections of copyright being extended to a huge volume of valueless (and often ownerless in the sense that no true owner can be identified or contacted) to protect a very small number of works of enduring economic value, though by no means does this promote the directive in the US Constitution "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries" (other nations have their own justifications).
While I'd love to see copyright terms just tuned down across the board, I could deal with a system whereby the next extensions required explicit renewals. For practicality's sake I might even be willing to put up with allowing owners to file one form for their entire catalog rather than enumerating everything, because if nothing else at least this would clear the zombie owner backlog.
I agree with this and I think you could even scale the fee for renewal up over time to discourage just automatic renewal of stuff that has almost no commercial value anymore. Seriously I could care less if disney wants to keep paying for steamboat willie to stay copyrighted as long as the fee keeps going up making them think about the value of doing so.
Initial copyright, until 1976, was for 28 years, registration required, with one renewal allowed for a total of 56 years (if I recall correctly).
While registration is still possible in the US (and is required for certain damages), it's not required. I agree that this would help greatly in addressing the matter of "orphan works".
Then there's the economic value of a work: very few copyrighted works have an economic life of one year, let alone a century. This is particularly true since copyright protections were extended to all works rather than just those which were registered with a copyright office (this post is copyrighted, however my economic interest in it is nil, still, it will extend for the next 120 years).
The real argument for extensions is copyright term in works of enduring value whose copyright is about to expire. This is the "Mickey Mouse Copyright Law" in the US. Walt Disney's first Mickey Mouse cartoon, "Steamboat Willie" (itself borrowing very heavily from earlier works) was published in 1928, and there's been a strong trend in extension to prevent works from at least this date from ever entering the public domain.
This results in the exceptionally strong protections of copyright being extended to a huge volume of valueless (and often ownerless in the sense that no true owner can be identified or contacted) to protect a very small number of works of enduring economic value, though by no means does this promote the directive in the US Constitution "To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries" (other nations have their own justifications).