OCLC has published a report (64 page pdf) that they commissioned on how libraries can reduce their carbon footprint through greener ILL practices. Nothing especially earth-shattering: The single most important finding of the study is that an ILL unit can cut its greenhouse gas emissions in half simply by re-using packaging materials.
A succint summation of the recommendations:
"The assumed effectiveness of common-sense practices to reduce ILL’s impact on the environment is borne out by scientific analysis:
• Re-use is preferable to New
• Ground is preferable to Air
• Near is preferable to Far
• Aggregation is preferable to 1X1
• Nylon bags are preferable to Plastic bins (unless the bins are always shipped full)
• 30% recycled paper equals New."