How about planting some trees ?
Check out
this project and discover how writing a blog can help the environment !
From their site :
How much carbon dioxide does your blog create?
According to a study by Alexander Wissner-Gross, PhD, physicist at Harvard University and environmental activist, an average website causes about 0.02g (0,0008oz.) of carbon dioxide for each visit. Assuming an average blog gets 15,000 visits a month, it has yearly carbon dioxide emissions of 3,6kg (8lb.). This can mainly be tracked back to the immense energy usage from (mainframe) computers, servers, and their cooling systems.
Now my blog doesn't get 15000 visitors a month but that won't stop me from helping out :)
I'll just have to get more visitors :)