As Christians, I think we come to Earth Day with slightly different motivations than our secular friends and neighbors- those motivations being more about stewardship than sustainability. Although sustainability really is good for consideration, ultimately we know that true sustainability comes only through the One who created everything in the first place.
It's interesting and strange to watch dialogue about global warming unfold among the Christian community. Why Earth care is not a major concern of the Church doesn't make sense to me. We believe (or at least I do) that Jesus will come back and restore and renew, but nevertheless, this Earth will remain (see Ephesians 1:9-10). Therefore, it's important that we are responsible with what God gives us- not just with relationships, talents, gifts, abilities, and time, but also with the physical resources with which He's blessed us.
All that being said, I admit that I have not done very well in doing my part. I like to talk about it, but it's so difficult for me to implement the things that I need to implement to be a more responsible Earthly resident.
So my Earth Day resolution is to go out and buy some fluorescent bulbs. I guess it's at least a start.