# Email Carbon Footprint: The Cost of 350 Billion Daily Messages Canonical: https://www.swizero.com/blog/email-carbon-footprint | Published: 2026-11-03 | Author: Chris Stefaner | Category: Industry > Your email carbon footprint adds up fast. Here's what 350 billion daily messages cost the planet in CO2 emissions, storage energy, and data center load. Nobody feels guilty sending an email. There's no exhaust pipe on your laptop, no smoke rising from your phone. But every message you send traverses a physical network of copper, fiber, and silicon, all of it powered by electricity, much of it generated by fossil fuels. According to Mike Berners-Lee's analysis for Lancaster University and OVO Energy, a single standard email produces roughly 4 grams of CO2 equivalent. An email with a large attachment can produce 50 grams. Multiply that by the [376 billion emails sent globally every day](https://www.swizero.com/blog/email-statistics-2026), and the numbers stop being trivial. Here's the uncomfortable part: the email carbon footprint problem isn't really about individual messages. It's about volume that nobody controls. Your inbox has no finish line, so it has no emissions ceiling either. > Key Takeaway > > A single email emits 0.3g to 50g of CO2 depending on its size and attachments. At 376 billion emails per day globally, that adds up to an estimated 140 to 300 million tonnes of CO2 equivalent annually. The biggest driver isn't sending; it's storing millions of unread messages on servers that never power down. ## How Does One Email Produce Carbon Emissions? Understanding your email carbon footprint starts with the three stages of a single message, none of which are visible to the person hitting send. **Transmission.** Your device converts text into data packets that travel through routers, switches, and undersea cables to reach a data center. Each hop consumes electricity. The International Energy Agency's 2025 report, [*Energy and AI*](https://www.iea.org/reports/energy-and-ai/energy-demand-from-ai), found that data centers consumed 485 terawatt-hours (TWh) of electricity in 2025, roughly 1.7% of global electricity consumption. Email is one slice of that demand. **Processing.** The receiving mail server must parse headers, run spam filters, apply rules, and index the message for search. The 2009 McAfee-funded study [*The Carbon Footprint of Spam*](https://www.siskinds.com/wp-content/uploads/carbonfootprint_12pg_web_rev_na-1.pdf), conducted by ICF International, found that spam filtering alone accounted for 16% of all spam-related energy use. The remaining 52% came from end users deleting junk and hunting for legitimate messages. **Storage.** This is where the real cost hides. Once delivered, your email lives on a server indefinitely. That server runs 24 hours a day, 365 days a year, drawing power for compute and cooling. The IEA projects data center electricity demand will [nearly double to 950 TWh by 2030](https://www.iea.org/news/data-centre-electricity-use-surged-in-2025-even-with-tightening-bottlenecks-driving-a-scramble-for-solutions). Every undeleted email contributes a fraction of that load. I could go on about network routing and DNS lookups, but the key insight is simpler: the email carbon footprint doesn't end when a message arrives. It compounds as long as it sits in storage. ## What Does Each Type of Email Actually Cost? Not all emails carry the same environmental weight. Mike Berners-Lee, Professor in Practice at Lancaster University's Environment Centre and author of [*How Bad Are Bananas?: The Carbon Footprint of Everything*](https://howbadarebananas.com/), published updated figures in 2020 that break down emissions by message type. | Email Type | CO2 Equivalent | Key Driver | | - | - | - | | Spam (filtered) | \~0.3 g | Server-side filtering only | | Short text email (no attachment) | \~4 g | Device + transmission + storage | | Email with attachment (1 MB) | \~19 g | Larger payload, longer storage | | Email with large attachment (5+ MB) | \~50 g | Heavy storage and repeated syncs | | Marketing newsletter (100 recipients, 1% read) | \~26 g per send | Bulk transmission, mostly unread | *Sources: Mike Berners-Lee, How Bad Are Bananas? (2020 revised edition); OVO Energy/Lancaster University, 2019.* These per-message numbers look small in isolation, but they are the building blocks of a much larger email carbon footprint. The problem is that nobody sends one email. The average office worker sends and receives [121 emails per day](https://www.radicati.com/wp/wp-content/uploads/2020/12/Email-Statistics-Report-2021-2025-Executive-Summary.pdf), according to the Radicati Group's *Email Statistics Report, 2021-2025*. At 4 grams each, that's nearly half a kilogram of CO2 per person, per day, just from plain text messages. **CO2 Emissions by Email Type (grams per message)** | Item | Value | | - | - | | Spam (filtered) | 0.3g CO₂e | | Text only | 4g CO₂e | | 1 MB attachment | 19g CO₂e | | 5+ MB attachment | 50g CO₂e | *Source: Mike Berners-Lee, How Bad Are Bananas? (2020)* ## How Big Is the Global Email Carbon Footprint? The honest answer: it depends on who's counting, and what they include. Estimates of email's total annual carbon emissions range from 140 million tonnes to over 300 million tonnes of CO2 equivalent. The wide range reflects methodological differences in what gets measured. Do you count only transmission energy, or also the upstream emissions of manufacturing servers, cooling infrastructure, and network equipment? The most widely cited figure comes from Berners-Lee's work with OVO Energy. Their [2019 study](https://www.ovoenergy.com/ovo-newsroom/press-releases/2019/november/think-before-you-thank-if-every-brit-sent-one-less-thank-you-email-a-day-we-would-save-16433-tonnes-of-carbon-a-year-the-same-as-81152-flights-to-madrid.html) focused on just the UK and found that 64 million unnecessary emails per day contributed 23,475 tonnes of carbon annually. Extrapolate to the global email volume of 376 billion daily messages, and the aggregate becomes significant. > "Whilst the carbon footprint of an email isn't huge, it's a great illustration of the broader principle that cutting the waste out of our lives is good for our wellbeing and good for the environment." > > — **Mike Berners-Lee**, Professor in Practice, Lancaster University Environment Centre For context, the IEA estimates that all data centers account for approximately 0.5% of global CO2 emissions. The global email carbon footprint is a meaningful subset of that total. It won't rival aviation or agriculture, but it sits in the same category as entire small nations' emissions. One caveat worth noting: these figures carry real uncertainty. The [Carbon Literacy Project's 2024 update](https://carbonliteracy.com/the-carbon-cost-of-an-email/) acknowledged that "estimates of the carbon footprint of an 'average' email vary widely, from fractions of a gram to tens of grams of CO2e per message." The disagreement stems from whether you count the energy to manufacture the devices reading the email, the proportion of a server's power attributable to one message, and how long storage lasts. The honest position is that email's footprint is real but hard to pin down precisely. ## Why Does Email Storage Matter More Than Sending? Most people assume the email carbon footprint is generated at the moment of sending. The bigger cost is storage, and it's a cost that grows every day you don't delete a message. Consider how storage works. A data center doesn't spin up a hard drive just for your email and then power it down. Your messages live on arrays of solid-state drives or spinning disks that run continuously, replicated across multiple locations for redundancy. Google, Microsoft, and other major providers maintain copies of your data in at least two geographically separate data centers. Every unread newsletter, every "sounds good!" reply, every promotional email you never opened occupies space on infrastructure that draws power around the clock. The IEA's data shows this infrastructure is growing fast. Data center electricity use [surged 17% in 2025 alone](https://www.iea.org/news/data-centre-electricity-use-surged-in-2025-even-with-tightening-bottlenecks-driving-a-scramble-for-solutions), driven partly by AI workloads but also by the relentless growth of stored data. Goldman Sachs projects data centers will consume 8% of US electricity by 2030, up from around 4% today. The connection to email is direct. If you have 10,000 unread messages sitting in your inbox (and [many people do](https://www.swizero.com/blog/email-overload-solution)), those messages aren't just cluttering your attention. They're consuming server resources, cooling capacity, and electricity in perpetuity. > **If the environmental cost of a bloated inbox concerns you,** [Swizero](https://www.swizero.com) reduces your inbox to a fixed card limit per session. Fewer messages processed means less time on screen, fewer server queries, and a smaller digital footprint per user. ## Is the "Send One Fewer Email" Advice Actually Useful? The OVO Energy/Lancaster University campaign asked Britons to "Think Before You Thank," arguing that if every UK adult sent one fewer unnecessary email per day, the country would save 16,433 tonnes of carbon annually, equivalent to 81,152 flights from London to Madrid. It's a memorable statistic. But is it the right framing? The skeptics have a point. As a [2020 Quartz analysis](https://qz.com/1937309/dont-worry-about-the-carbon-footprint-of-your-emails) argued, individual email restraint is a rounding error compared to systemic energy choices. Switching a data center from coal to renewable power dwarfs any behavioral nudge about thank-you emails. Focusing on individual guilt risks letting infrastructure operators off the hook. But here's what the skeptics miss: volume drives infrastructure. Every additional email stored is a vote for more servers, more cooling towers, more power lines. The relationship between email volume and energy consumption isn't linear (efficiency improvements help), but it isn't zero either. Reducing [unnecessary email volume](https://www.swizero.com/blog/process-email-faster) addresses the demand side of the equation. The research from the McAfee/ICF study makes this concrete. Of all spam-related energy consumption, 52% came from end users managing unwanted messages, not from sending or filtering them. The energy cost of email overload lands squarely on the people drowning in it. This is where the environmental argument aligns with the productivity argument. The practices that [reduce email's cognitive burden](https://www.swizero.com/blog/email-habits-that-actually-work-according-to-science) also reduce its environmental burden: fewer unnecessary messages sent, less time spent on devices, less data stored on servers that never sleep. ## What Actually Moves the Needle on Email's Environmental Impact? Individual behavior matters, but systemic choices matter more. Here's what the research suggests, ranked by impact. ### Renewable-powered data centers Google reported an average power usage effectiveness (PUE) of 1.09 in 2024, compared to an industry average of 1.56. Google has also committed to running on 24/7 carbon-free energy. When your email provider runs on renewables, the per-message footprint drops dramatically, regardless of your behavior. ### Spam reduction at the infrastructure level The McAfee/ICF study found that spam accounted for 33 billion kilowatt-hours annually in 2008. Improved spam filtering since then has reduced per-user spam exposure significantly, but spam still represents roughly [45% of all email traffic](https://www.swizero.com/blog/email-statistics-2026). Every spam message blocked before delivery saves transmission, processing, and storage energy. ### Deliberate email hygiene Unsubscribing from newsletters you don't read, deleting old messages, and sending fewer unnecessary replies all reduce storage load. The Swizero approach of constraining email to a [finite session](https://www.swizero.com/blog/email-finish-line) means less time on devices and fewer server round-trips per user. ### Attachment optimization Berners-Lee's data shows a 12x difference in emissions between a plain text email (4g) and one with a 5+ MB attachment (50g). Linking to cloud documents instead of attaching files reduces both the email's size and the redundant copies stored across sender and recipient servers. ## How Does Email Compare to Other Daily Activities? Perspective matters when assessing your email carbon footprint. Here's where email sits relative to other common carbon sources. Berners-Lee's framework from [*How Bad Are Bananas?*](https://howbadarebananas.com/) puts a year of personal email use (including attachments) at roughly 135 kg of CO2 for the average office worker. For comparison: - A single transatlantic flight produces approximately 1,600 kg of CO2 per passenger - Driving a mid-size car for a year produces roughly 4,600 kg of CO2 - Heating an average UK home for a year produces about 2,700 kg of CO2 - Streaming one hour of video produces about 36 g of CO2 (Netflix estimate) So yes, your email carbon footprint is smaller than your commute or your heating bill. But 135 kg is not nothing. It's roughly equivalent to driving 340 miles. And unlike your commute, email's carbon cost is almost entirely invisible and entirely unmanaged. The aggregate picture is what matters. With 4.5 billion email users worldwide, even small per-user emissions add up. If every user reduced their stored email volume by 20%, the reduction in data center storage load would be measurable at the grid level. ## The Finish Line Argument, Applied to Carbon Here's the part that most "green email" guides miss. They tell you to send fewer emails. They tell you to unsubscribe from newsletters. They tell you to compress attachments. All fine advice. But none of it addresses the structural problem: email is unbounded, so email's environmental cost is unbounded too. The same principle that makes email psychologically exhausting (there's always more) makes it environmentally wasteful. An inbox with no endpoint means infinite scrolling, which means infinite server queries, infinite sync cycles, infinite storage growth. You can't audit what you can't bound. [Swizero's approach](https://www.swizero.com/blog/inbox-zero-alternative) constrains email to a fixed card limit per session. You see what matters, act on it, and stop. The environmental case is the same as the productivity case: bounded systems consume fewer resources than unbounded ones. When [you check email in defined sessions](https://www.swizero.com/blog/how-often-should-you-check-email) rather than monitoring it continuously, your device spends less time polling servers, your attention consumes less energy, and fewer unread messages accumulate in storage. That's not a solution to climate change. But it's a better default than the one most people are running. ## Frequently Asked Questions ### How much CO2 does a single email produce? A spam email that gets caught by filters produces about 0.3 grams of CO2 equivalent. A standard text email produces roughly 4 grams. An email with a large attachment (5+ MB) can produce up to 50 grams. These figures come from Mike Berners-Lee's analysis published in *How Bad Are Bananas?* (2020 revised edition), commissioned in part by OVO Energy and Lancaster University. ### What is the total annual email carbon footprint worldwide? Estimates range from 140 to 300 million tonnes of CO2 equivalent per year, depending on methodology. The wide range reflects differences in what's counted: transmission energy alone is relatively small, but adding storage, device energy, and infrastructure manufacturing significantly increases the total. No single authoritative figure exists because email's footprint overlaps with broader data center and network emissions. ### Does deleting old emails actually help the environment? Yes, though the impact per individual is small. Deleting stored emails reduces the amount of data that servers must maintain, replicate, and back up across multiple data centers. At scale, reduced storage demand means fewer servers provisioned and less cooling required. The benefit is most meaningful for organizations managing millions of mailboxes. ### Is email worse for the environment than a physical letter? A standard physical letter produces roughly 29 grams of CO2 according to Royal Mail's carbon audit, factoring in paper production, printing, and transportation. A plain text email at 4 grams is significantly lower. However, the volume difference matters: most people send far more emails than they would physical letters, and emails persist in storage indefinitely while letters eventually decompose or get recycled. ### Are "green email" browser extensions effective at reducing your email carbon footprint? Tools like OVO Energy's Carbon Capper flag short, potentially unnecessary emails before you send them. They raise awareness, which has some value. But the most effective changes happen at the infrastructure level: data centers switching to renewable energy, better spam filtering, and email systems designed to reduce rather than encourage message volume. Individual tools help, but they address a small fraction of the total footprint. ## Sources 1. [How Bad Are Bananas?: The Carbon Footprint of Everything](https://howbadarebananas.com/) - Mike Berners-Lee, Profile Books, 2020 (revised edition). Per-email CO2 estimates by type: 0.3g (spam) to 50g (large attachment). 2. [Think Before You Thank](https://www.ovoenergy.com/ovo-newsroom/press-releases/2019/november/think-before-you-thank-if-every-brit-sent-one-less-thank-you-email-a-day-we-would-save-16433-tonnes-of-carbon-a-year-the-same-as-81152-flights-to-madrid.html) - OVO Energy / Lancaster University, November 2019. UK unnecessary emails produce 23,475 tonnes of carbon annually. 3. [Data Centre Electricity Use Surged in 2025](https://www.iea.org/news/data-centre-electricity-use-surged-in-2025-even-with-tightening-bottlenecks-driving-a-scramble-for-solutions) - International Energy Agency, 2025. Data centers consumed 485 TWh in 2025, up 17% year-over-year. 4. [Energy and AI: Energy Demand from AI](https://www.iea.org/reports/energy-and-ai/energy-demand-from-ai) - International Energy Agency, 2025. Data center electricity projected to reach 950 TWh by 2030. 5. [The Carbon Footprint of Spam Report](https://www.siskinds.com/wp-content/uploads/carbonfootprint_12pg_web_rev_na-1.pdf) - ICF International / McAfee, 2009. Spam generated 33 billion kWh and 17 million tonnes CO2 annually. 6. [Email Statistics Report, 2021-2025](https://www.radicati.com/wp/wp-content/uploads/2020/12/Email-Statistics-Report-2021-2025-Executive-Summary.pdf) - Radicati Group. 121 emails per day per office worker, 376.4 billion daily global volume. 7. [The Carbon Cost of an Email: Update](https://carbonliteracy.com/the-carbon-cost-of-an-email/) - The Carbon Literacy Project, 2024. Acknowledges wide variance in per-email estimates and methodological challenges. 8. [Don't Worry About the Carbon Footprint of Your Emails](https://qz.com/1937309/dont-worry-about-the-carbon-footprint-of-your-emails) - Quartz, 2020. Skeptical analysis arguing systemic changes outweigh individual email behavior.