You can read more about how it works from this website as well. In general, "An average blog causes 3.6kg (8lb.) of carbon dioxide emissions. Consequently, a tree neutralises the carbon dioxide emissions of a blog. Since a tree lives for an average of 50 years, carbon dioxide emissions of your blog can be completely neutralised for this time period."
I believe that every little bit of effort does help. So if you are interested (like me) in joining this, you can read more here. Happy belated Earth Day everyone! :D
I have received an email from Christin Gericke thanking me for the participation on this.