In a white paper comparing the carbon footprint and energy usage associated with various forms of music delivery, from CDs sold at retail to CDs sold on the Internet to simple downloads, it's not surprising that the downloads have the least environmental impact.
Purchasing music digitally reduced CO2 emissions associated with delivering music to consumers by 40-80 percent, as compared to buying a CD at retail.
The research took into account all facets, from packaging to type of shipping involved.
The white paper, "The Energy and Climate Change Impacts of Different Music Delivery Methods," (PDF download) was sponsored by Microsoft and Intel. The report was prepared by the Department of Civil Engineering and Environmental Engineering at Carnegie Mellon University and the Lawrence Berkeley National Laboratory at Stanford University.