Following up on last year's question of "What's the carbon footprint of sending a text message?" (0.000003 grams of CO² used by the network, excluding external factors such as making the phone), The Guardian has now asked "What's the carbon footprint of making a mobile phone call?"
Climate change expert Mike Berners-Lee has considered rather more than the earlier article, factoring in phone manufacture and network administration alongside power consumption. His answer is that a minute's mobile-to-mobile call will generate 57g of carbon, which means a three-minute call appears to have a similar environmental impact to sending a letter in the post.