Spam emails produce as much greenhouse gas emissions each year as 3.1 million cars, according to research for computer protection company McAfee.
The study showed that globally, spam uses 33 billion kilowatt hours (KWh) a year, enough energy to power 2.4 million homes.
The research also found that the UK was the joint fourth biggest emitter of CO2 from spam in the world, creating 50,000 tonnes of carbon dioxide a year.
The Carbon Footprint of Spam study by researchers ICF said that nearly four-fifths of the energy use associated with the emails was in end users deleting spam and searching for legitimate emails.
The report also claimed that spam filtering currently saved enough energy to reduce emissions equivalent to taking 13 million cars off the road.
Jeff Green, senior vice-president of product development and McAfee Avert Labs, said: “As the world faces the growing problem of climate change, this study highlights that spam has an immense financial, personal and environmental impact on businesses and individuals.
“Stopping spam at its source, as well as investing in state-of-the-art spam filtering technology, will save time and money and will pay dividends to the planet.”