Notes

Section 1.01 The carbon footprint of using a mobile phone:
47kg CO2e: a year's typical usage of just under 2 minutes per day
1250kg CO2e: a year's usage at 1 hour per day
125 million tons CO2e: global mobile usage per year
A minute's mobile-to-mobile chatter comes in at 57g, about the same as an apple, most of a banana or a very large gulp of beer. Three minutes has a similar impact to sending a small letter (written on recycled paper) by second-class post.
Mobile phones cause a fairly tiny slice of global emissions, but if you are a chatterbox using your mobile for an hour each day, the total adds up to more than 1 ton CO2e per year – the equivalent of flying from London to New York, one way, in economy class.
Indeed, the footprint of your mobile phone use is overwhelmingly determined by the simple question of how often you use it. One estimate for the emissions caused by manufacturing the phone itself is just 16kg CO2e, equivalent to nearly 1kg of beef. If you include the power it consumes over two typical years (that's about how long the average phone remains in use, even though most could probably last for 10 years) that figure rises to 22kg.
But the footprint of the energy required to transmit your calls across the network is about three times this entire put together, taking us to a best estimate of 94kg CO2e over the life of the phone, or 47kg per year. This breaks down as follows:
Base station 23.1kg
Administration 7.1kg
Manufacture 6.3kg
Switchboard 5.6kg
Phone energy 3.2kg
Transport before sale 1.6kg
In 2009 there were 2.7 billion mobiles in use: nearly half the world population has got one. On this basis, mobile calls account for about 125 million tons CO2e, which is just over one-quarter of a per cent of global emissions.
If you want to reduce the footprint of your communication habits, texting is a much lower-carbon option. Landlines offer carbon savings, too, because it takes about one-third of the power to transmit a call over a fixed landline network than it does when both callers are on a mobile.

It took a lot of digging to get data for these calculations. In the end I was pleasantly surprised that there is some reasonably sensible looking analysis out there. Nevertheless, now feels like a good time for a reminder that all footprint estimates contain considerable uncertainty – and some more than others.