Sending a text message or email, eating an apple or watching TV -- each of these activities has a different carbon footprint.
People around the world are getting ready to mark Earth Hour by turning out the lights on Saturday, but a long list of seemingly harmless everyday actions also contribute to emissions of carbon dioxide and other planet-harming greenhouse gases.
Total global emissions in 2010 were estimated at 49 gigatonnes of CO2 equivalent.
Email and Internet
Even a short email is estimated to have a footprint of four grammes of CO2e -- including greenhouse gases produced in running the computer, server and routers and a part of their manufacture.
An email with a large attachment emits about 50 gCO2e, and a spam message, not even opened by the recipient, is responsible for 0.3 gCO2e.
The annual global footprint of spam is equivalent to 3.1 million passenger cars on the road in a year, using 7.6 billion litres of gasoline.
A web search on an energy-efficient laptop leaves a footprint of 0.2 gCO2e, and on an old desktop computer some 4.5 gCO2e.
A cellphone text message comes at a cost of about 0.014 gCO2e.
Shopping
A plastic carrier bag leaves a footprint of 10 gCO2e, and a paper bag 40 gCO2e.
Drinking
About 473 millilitres of water from the tap generates 0.14 gCO2e compared to 160 gCO2e for a 500 ml store-bought bottle.
A large cappuccino comes at 235 gCO2e, compared to 21 gCO2e for a cup of black coffee or tea for which just enough water was boiled.
Leisure
An hour of TV watching on a 38-centimetre LCD screen yields 34 gCO2e, compared to 88 gCO2e on a 81.3-centimetre LCD screen, and 220 gCO2e on a 61-centimetre plasma screen.
While 1.6 kilometres of cycling powered by a meal of bananas would be responsible for 65 gCO2e, compared to 260 gCO2e for 1.6 kilometres powered by cheeseburgers.
Sources: "How Bad Are Bananas" by Mike Berners-Lee, Fifth Assessment Report of the UN's Intergovernmental Panel on Climate Change, McAfee study "Carbon Footprint of Spam".
