Security vendor McAfee has released a report on the carbon footprint of spam, in which it tries to estimate the environmental costs of spam. According to the report, each spam generates the equivalent of 0.3g of CO2, making the yearly impact of spam equivalent to driving a car round the Earth 1.6 million times.

The report has generated a lot of rather breathless news coverage (such as this piece from ABC), causing the media's flagging interest in spam to perk up again, at least for a moment. For McAfee, the answer is for businesses to install state-of-the-art spam-filters, a conclusion that was probably not in any way influenced by the fact that McAfee happens to sell enterprise spam-filtering software.

Several commentators have expressed some cautious skepticism about the findings. David Coursey writing in PCWorld suggests that it may make unrealistic assumptions about power management. John Timmer in ArsTechnica has written a more in-depth look at the McAfee study. He observes that the largest energy costs documented in the study come from users using their computers to manually review and delete spam. That squares with McAfee's conclusion — catching the spam earlier can save energy — but Timmer finds the report's authors curiously unforthcoming about the calculations that underlie their estimates of the energy cost associated with user filtering.

Manual spam filtering obviously has higher costs than the largely automated (and often computationally-trivial) steps that make up the rest of the spam lifecycle. In addition to supporting the energy overhead of a modern desktop OS and GUI, power is needed to drive the monitor. But once you start worrying about that, why stop with spam? Why aren't we worried about the planet-raping impact of Minesweeper or World of Warcraft? What are lolcats and Facebook doing to the Amazon rainforest?

It's also worth looking at the other side of the equation. Spammers often make the claim that spam is environmentally friendly, because it reduces demand for paper. This argument is probably specious. If there were no such thing as email spam, I doubt that I'd be getting hundreds of paper letters per day urging me to enlarge my penis or buy fake watches. There's little reason to think that most of the 'legitimate' small business that use mom'n'pop commercial bulkmailers to send unsolicited mail would be bothering me with paper mail either. (I know that all the Peruvians who are currently bombarding me with ads for business training seminars or local pizzerias would be a lot more careful with their mailing list management if they had to pay international postal rates). Would it be better for the environment if the companies that currently clog my mailbox with paper catalogs and special offers switched to sending unsolicited email? Probably, but despite the best efforts of the sponsors of spam-friendly legislation, the big boys know that spam is poison to their business. More importantly, they know that spam can be filtered. They can pay the Post Office to put their junk in my mailbox, but; they can't pay my mailserver not to silently throw away everything they send me. If there's a future in email marketing for big corporations, it lies in solicited email, in the form of properly-run mailing lists. A 'best practice' mailing list delivers only useful information to people who actually want to receive it. Rather than being a curse, like spam or paper junk mail, it's a potential win for everyone — including the planet.

There's no reason to think that spam is good for the planet, but it's unclear whether it's really as destructive as the McAfee study suggests. The claims made in the study seem to rest on some rather uncertain and underdocumented assumptions.

There are plenty of reasons to hate spam, but its carbon footprint is probably pretty far down the list.