The carbon footprint of...books?

Amazon's Kindle claims that a single Kindle displaces the purchase of 22.5 books each year for an estimated carbon savings of 168 kg of CO2. If the full storage capacity of the Kindle is used, the device prevents the equivalent of almost 11,185 kg of CO2 from being released.

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Also, "shipped books are still twice as carbon efficient as books bought in the mall or the local bookstore."

I think books should be given a CO2 pass.