Our Metro DC Synod recently had an assembly where we put emphasis on Creation Care. Click here for a slide show of the great things our congregations are doing. Also I've written alternative lyrics for "Joyful Joyful We Adore Thee" based on local congregations' eco-stewardship (please be ready to smile and remember that my rhyming skills are not exactly a spiritual gift...).
The biggest thing the assembly did to go green was hold the meetings locally. Using rough estimates, we probably cut down our travel costs (including environmental costs) by 70%. Plugging the numbers into a fairly standard carbon calculator we found that it took 10 trees a year to cover the carbon used per person for last year's assembly down in Roanoke, VA.(That assumes carpooling of 2 pple per car and a start from downtown DC) . For the local assemblies it was more like 3 trees (also assuming 2 pple per car and averaging starting mileage across the synod).
These calculations shouldn't be quoted in any way but real approximations, but they do indicate that holding the assembly locally was a big environmental savings.