A survey of 10,076 households conducted by the NPD Group Inc in the US found that computers switched on at homes sit idle for 54 per cent of the time. The Sierra Club, a group of environmentalists, has estimated that a computer running for more than three hours a day is responsible for 200 pounds of carbon dioxide (C02 ) emission every year. This is two per cent of the annual C02 emission by a car - which is actually doing something (Tomorrow. Global Environment Business, Vol 7, No 3).