Emails are a ubiquitous part of modern life, with billions being sent and received daily. While each email may seem insignificant in terms of environmental impact, the collective footprint of these digital communications can be substantial.

In fact, emails are a prime example of the so-called rebound effect, where the adoption of an environmentally-friendly technology leads to increased usage, thereby offsetting the environmental benefits. Despite an email having a much smaller carbon footprint than sending a handwritten letter, the sheer volume of emails sent daily far exceeds the number of letters ever posted.

Email using is increasing, with the number of global email users expected to grow from 3.7 billion in 2017 to 4.7 billion in 2026. As a result, it’s important to understand the contribution of email to the climate crisis and how we can mitigate it.

What’s the average carbon footprint of an email?

According to carbon footprint guru Mike Berners-Lee in his book "How Bad Are Bananas?", the average carbon footprint of an email is approximately 0.3g CO2e. However, this varies wildly depending on the nature of the email that’s being sent. For example:

• Spam email filtered out: 0.03g CO2e
• Short email sent from a phone: 0.2g CO2e
• Short email sent from a laptop: 0.3g CO2e
• Long email with an attachment: Up to 50g CO2e

Why the variation? Well, sending an email generates emissions across a few key stages:

• The sender’s device: typing the email out
• The data centres: providing storage and serves to facilitate the email
• The receiver’s device: to load and read the email

The footprint generated at each stage includes the energy used to power the devices and data centres, as well as the embodied emissions for manufacturing the equipment.

Data centers, which store and transmit emails, now have a carbon footprint exceeding that of pre-COVID air travel. Since only 30% of the global power grid is sourced from renewable energy, the majority of this digital infrastructure is powered by fossil fuels. Most devices are also powered by energy that includes a mix of renewable and fossil-fuel based sources.

As a result, if you take a while to write an email (using more energy on your device), make it long and add an attachment (so data centres work harder to transmit the email), and send it to 10 people who all read the email in depth (using even more energy on multiple devices)... the email will have a much larger footprint than a spam email that no one reads!

But that’s not to let spam emails off the hook – the sheer volume of spam emails that are sent daily means that their impact adds up.

How can you measure the emissions from your own emails?

In an ideal world, you’d be able to see the emissions associated with your email as you’re writing it, and take action there and then. However, because the emissions happen in various places across the complex IT landscape, it’s a very difficult metric to track accurately.

The energy used to power your own devices will be reflected in your energy bills (if you charge the device at home or, as a business, in the office). However, unless your recipients are in the same home or office then their device energy won’t be part of your bills.

As for data centres, Microsoft provide an impact dashboard which tracks the emissions from powering a range of Microsoft services, including the email exchange. You can set this up here.

What’s the best way to reduce the emissions from your emails?

While emails themselves aren't the biggest carbon problem, they are part of a rapidly growing digital system. Here are some practical steps to reduce your email-related carbon footprint:

1. Send fewer unnecessary emails: Not only does this reduce emissions, but it also improves productivity and mental health.
2. Minimize CCs and BCCs: Only include people who need to be in the loop, and consider sending a single summary email instead of multiple updates.
3. Use links instead of attachments: This reduces the data load and the associated emissions.
4. Delete old emails: This reduces the energy required to store them in data centers.
5. Unsubscribe from unwanted mailing lists: This helps to decrease the volume of spam and irrelevant emails.

While emails may seem inconsequential individually, their collective impact is substantial. By adopting these simple practices, you can contribute to reducing the overall carbon footprint of our digital communications.

Reducing email volume is not only good for the planet but also beneficial for managing stress and increasing productivity. As we continue to rely on digital technologies, being aware of their environmental impact and taking steps to mitigate it can lead to more sustainable practices in our everyday lives.

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