What is the carbon footprint of an email?

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 (CO2) and other planet-harming greenhouse gases.

Total global emissions in 2010 were estimated at 49 gigatonnes (Gt or billion tonnes) of CO2 equivalent (CO2e).

Email and Internet

Even a short email is estimated to have a footprint of four grammes (0.14 ounces) of CO2e (gCO2e) -- 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 two billion gallons (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
A pint (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 15-inch (38-centimetre) LCD screen yields 34 gCO2e, compared to 88 gCO2e on a 32-inch LCD screen, and 220 gCO2e on a 24-inch plasma screen.

A mile of cycling powered by a meal of bananas would be responsible for 65 gCO2e, compared to 260 gCO2e for a mile powered by cheeseburgers.