Earth Day spurred some conversation on NTEN Discuss about how to figure out carbon emissions for every watt a computer uses per hour. Dean Matsueda wrote that he had seen and used carbon-footprint calculators online to gauge household, car, and air travel C02 emissions but would like to drill down to more specifics, like computer use.

Walt Daniels gave this response:

Carbon footprint is a simple multiply if you have the watts/hr and number of hours. watts/hr is what is hard to come by for most computer setups unless you have a meter on it because the usage depends on too many things,like duty cycle and how you have the power savings features on your computer set.

Gavin Clabaugh lets us know that to do it right, you need to meter the machine. He uses a Kill-A-Watt (a simple one costs about $20).

And Dave Shaw, H4 Consulting, added: