Modern web-development and environmental awareness are no opposites.
Both my office as well as the data center that houses the servers use "green" power.

All comps, routers and coffee makers in my office are 100% running on power generated from water, sun, wind and biomass, delivered by "Naturstrom". Whereas the servers (in the Hetzner Data Center) are powered by "Naturenergie", another green power provider. 

This means that both developing- as well es running the websites gives you a comfy green conscience.