Anyone with an email account knows that spam is a nuisance, but as well as wasting time, unsolicited emails are also guilty of wasting huge quantities of energy, according to new research released today.

The study from environmental research firm ICF was commissioned by security software firm McAfee and found that the 63 trillion spam email messages sent each year waste 33 terawatt-hours of energy -- enough to power 2.4m homes.

The research also assessed the carbon footprint associated with individual email messages and found the average message results in 0.3g of CO2 being emitted.

Dave Marcus, security research and communications director at McAfee, told BusinessGreen.com that while each individual email resulted in just a "tiny puff of CO2" the global spam epidemic meant that overall unsolicited emails resulted in carbon emissions equivalent to those produced by 3.1m passenger cars.

"There is an energy cost with the transaction, storage and deletion of any email," he said. "When you add it up, we are talking about a significant impact."

Marcus argued that while firms could not eradicate spam completely, they could limit its carbon impact by implementing software and policies designed to intercept messages before they reach staff.

"The research showed that 80 per cent of the energy use associated with spam came from the user pruning their email account," he explained. "The opening, closing and deletion of the message is the most energy-intensive part of the process as the loading of images and text has a processor and heat cost that translates to energy use."