"When you look at it from an individual user perspective you're only talking about 0.3 grams of carbon dioxide per spam message," said Dave Marcus, director of security research and communications at McAfee’s Avert Labs, in a telephone interview. "When you extrapolate the math out to the larger numbers, it definitely is significant."

The McAfee , which was written by consulting company ICF International, said the estimated 62 trillion spam e-mail that get sent each year consume 33 billion kilowatt hours of electricity, enough to power 2.4 million homes. In addition, spam e-mail releases as much carbon dioxide into the atmosphere as 3.1 million cars consuming 2 billion gallons of gasoline.