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The Carbon Cost of an Email: Update!
Photo by Stephen Phillips on Unsplash
Emails. Most of us receive hundreds of them every day. We send a lot too. According to Statista, more than 306 billion emails were sent in 2021 and that is expected to top 376 billion in 2025. While each one may seem fairly innocuous, the collective impact of billions of emails can soon add up. But just how significant is the impact of all those emails?
In this update to our earlier and most popular blog, we once again explore the carbon cost of an email.
Calculating the emissions generated by an email is no easy task. It depends on the device used to create the email, whether it is the latest phone or an old desktop computer. You then must factor in how long it took for the sender to write it and the reader to read it. Did the sender add pictures, attach a big document, or sign off with a signature including the company logo? Then there is the energy used to send it and how efficient the various data centres are through which it passes. All these things have an impact. So, the best we can come up with is a range.
In the latest version of his book, ‘How Bad are Bananas?: The Carbon Footprint of Everything’ (2020), Mike Berners-Lee puts that range at between 0.03g and 26g. That is less than the estimates in his earlier work – partly because devices and data centres are becoming more efficient. But as we have mentioned, the number of emails is going up.
So how do different types of email stack up? At the low end are spam emails that have been picked up by your spam filters and never even make it to your inbox. That’s around half of all the emails that are ever sent. At the other end are mass mailings that take a long time to write, but only ever get read by a few people.
| Email Type | Emissions (CO2e) |
| Spam email picked up by your filters | 0.03 g |
| Short email sent and received on a phone | 0.2 g |
| Short email sent and received on a laptop | 0.3 g |
| Long email that takes 10 minutes to write and 3 minutes to read sent and received on a laptop | 17 g |
| Email blast that takes 10 minutes to write and sent to 100 people, of whom 1 reads it and the other 99 glance at it for 3 seconds to decide that they should ignore it | 26 g |
Do I need to worry?
Berners-Lee estimates that globally emails could account for as much as 150m tonnes CO2e in 2019, or about 0.3% of the world’s carbon footprint. That is based on around half of all emails sent being spam and the remainder being reasonably useful messages that took the sender 3 minutes to write and the reader about 1 minute to read. On that basis, average email usage is equivalent to driving a small petrol car for around 128 miles.
In the grand scheme of things, the impact of email is not the biggest carbon problem humanity faces, but it is an easy one to tackle. Berners-Lee acknowledges that thinking about email is a good way into conversations about ‘the benefits of cutting every kind of junk out of our lives’.
There are a number of things that you can do that not only keep email volumes to a minimum, but are also beneficial to tackle the stress and anxiety that comes from email overload:
- Only subscribe to news services that you want
- Unsubscribe from mailing lists that are no longer relevant to you
- Ensure the mailing lists you use are up to date
- Write concisely and keep messages as brief as possible
- Only message those who need the information; don’t copy people in simply to cover your own back
These simple and easy tactics could be good for you, as well as for the planet, and are things you can do right now from wherever you may be sitting reading this.