This report from McAfee finds that the energy consumed in transmitting and deleting junk email equals the amount of energy used by 2.4 million U.S. homes.

Among the findings from the report:

• An estimated worldwide total of 62 trillion spam emails were sent in 2008;
• Globally, annual spam energy use totals 33 billion kilowatt-hours (KWh), or 33 terawatt hours (TWh). That’s equivalent to the electricity used in 2.4 million homes in the United States, with the same GHG emissions as 3.1 million passenger cars using two billion United States gallons of gasoline;
• Spam filtering saves 135 TWh of electricity per year. That’s like taking 13 million cars off the road;
• The average GHG emission associated with a single spam message is 0.3 grams of CO2. That’s like driving three feet (one meter) in equivalent emissions, but when multiplied by the annual volume of spam, it’s like driving around the Earth 1.6 million times; • A year’s email at a typical medium-size business uses 50,000 KWh; more than one fifth of that annual use can be associated with spam

The full report is available for free download from McAfee.com.