“While environmentalist groups have benefited from social networking, keeping the Web working emits a lot of CO2” (Source: Mother Nature Network)
Very interesting story about the contradictions of environmental online campaigning.
From the same article:
“In emails alone, the typical officeworker is responsible for 13.6 tons of CO2 or its equivalent per year, a French government agency for energy efficiency, ADEME, calculated last year.
That figure is based on a French company of 100 people who work 220 days a year and each receive 58 mails a day and send 33 per day, with an average mail size of one megabyte.
By comparison, 13.6 tons is more than twice the annual CO2 emissions per capita in France and almost two-thirds of the average annual emissions per capita in the US.”
3eintelligence.wordpress.com 
I’m extremely sceptical of these kind of calculations. Most of the CO2 emitted in the context of ICT is in the manufacture of the devices and servers and the production of the power needed to keep them running. So the number will vary hugely depending on whether a user is a gadget freak replacing his smartphone, tablet and PC every time a new model comes out or someone who keeps them working until they die, which typically means 4-8 years for a PC. It depends what else one does with the PC: a machine used exclusively for the odd email and otherwise left idle, or a nerd’s machine that does a thousand other things as well?
Finally, one has to compare like with like. If I don’t send an email but instead use a pen to write the message on a piece of paper, slip this into an envelope, stick on a stamp, drive to the post office, drop it, etc., my footprint will be far higher than if I send one additional email by PC.
You get my point. Yes, devices and servers consumer power and resources, and their manufacture, transport, and disposal pollutes. But figuring out how much pollution to allocate to one discrete activity such as an email is a complete waste of time that risks getting people to veer off into directions as stupid and irrelevant when it comes to mitigating pollution and GHG emissions as the ban on incandescent light bulbs.