Digital Media

This chart describes the percentage of greenhouse gas emissions associated with each component of spam energy use.

(Credit: ICF/McAfee)

Not only is spam a nuisance and sometimes criminally deceptive, it's got a carbon footprint.

The mere act of people around the world deleting spam and searching for legitimate e-mail falsely labeled as junk creates the annual energy consumption equivalent in the U.S. of 2.4 million homes using electricity and the same greenhouse gas emissions as 3.1 million passenger cars using two billion gallons of gas.

That's according to "The Carbon Footprint of Email Spam Report" conducted by climate-change consultants ICF and commissioned by security vendor McAfee.

The average greenhouse gas emission associated with one spam message is 0.3 grams of CO2, about the same as driving three feet in equivalent emissions. When multiplied by the 62 trillion spam e-mails sent globally, that is like driving around the Earth 1.6 million times.

Eighty percent of the energy consumption associated with spam messages come from people having to do spam maintenance, the report found. Spam filtering accounts for only 16 percent of the energy use and saves the electrical equivalent of taking 13 million cars off the road per year.

If spam filters were used universally, the energy saved would be equivalent to taking 2.3 million cars off the road, the report said.

When major spam-hosting provider McColo was taken offline last November, global spam volume dropped by 70 percent overnight. That was the equivalent of taking 2.2 million cars off the road. Unfortunately, spam levels are back up as the spammers found other places to host their spam command-and-control servers.