Utilities. Automotive. Aviation. Industries known for carbon emissions. But the internet? That's right, the world wide web eats a lot of energy - with an ever growing appetite as we trade more emails, pictures and videos online.

An estimated billion and a half people are online around the world. And the net's energy footprint is growing by more than 10% each year. At the heart of it are big websites: search engines, social networking sites and video sharing sites. They require vast datacenters: on average, they consume the same amount of energy as 25,000 households.

So, what is the internet's carbon footprint? A report conducted by the Climate Group estimates by 2020, it will have nearly tripled, to a billion and half tons of carbon dioxide emitted per year. But the report also says improvements can help. Smart energy-aware buildings and more efficient energy grids. More efficient cooling and switching to renewable resources can help the internet run smoothly, and cleanly.