62 trillion spam emails are sent every year, amounting to emissions of more than 17 million tons of carbon dioxide, one of the main contributors to global warming. More effective spam filtering could reduce the amount by 75%, which would be the equivalent of taking 2.3 million cars off the road. This would not deal with the extra energy being used to send out the messages in the first place, however. A better strategy would be to fight spam at the source. When one global web hosting firm was taken offline after it was found to have ties to spammers, global spam volume fell briefly by 70%.