Carbon Neutral Events

This is a first - Iceberg Events have been asked to bid on an event, and one of the criteria is that the event be carbon neutral. I'll be addressing this in a number of ways, including adding in costs for Carbon Neutral as a line item in the budget; and assessing the venue, caterers and other suppliers on their environmental policies. Obviously we'll be assessing our own practices here as part of the process as well. Does anyone out there have any thoughts on this? I'm open to suggestions and new ideas here - I'm certain that this will become more common, especially for events which are dealing with environmental issues and the future.