Produced by ChatGPT o3; 2025-05-16; thought for 1m28s – see Appendix
Explore the veracity of this claim:
Based on the older figures, some people have estimated that their own emails will generate 1.6kg (3.5lb) CO2e in a single day. Berners-Lee himself also calculated that a typical business user creates 135kg (298lbs) CO2e from sending emails every year, which is the equivalent of driving 200 miles in a family car.
In short: The figures of 1.6 kg of CO₂e per day and 135 kg of CO₂e per year trace back to Mike Berners-Lee’s first-edition calculations (2010) that put a “standard” email at roughly 4 g CO₂e. Multiplying that by ≈ 400 messages a day gives 1.6 kg, while ≈ 33 000 messages a year gives 135 kg – hence the BBC’s oft-quoted comparison with a 200-mile car journey. Since then, better data-centre efficiencies and greener electricity have driven the per-email footprint down to 0.2 – 0.3 g CO₂e for a short message and 17 g for a long, attachment-heavy one. Using today’s averages (about 40 emails sent per worker per day and 0.3 g each) a typical user now creates nearer 3–5 kg CO₂e per year – two orders of magnitude lower than the 135 kg headline. The original numbers are therefore _technically correct for the assumptions used at the time* but wildly over-state modern reality unless you are an exceptionally heavy emailer or routinely send large attachments.
| Source | Key numbers (2010) |
|---|---|
| How Bad Are Bananas? (1st ed.) – Mike Berners-Lee | 0.3 g for spam; 4 g for a “standard” email; 50 g for an email with big attachments (The Carbon Literacy Project) |
| BBC Future feature | Quotes Berners-Lee and reports “typical business user = 135 kg CO₂e yr⁻¹ ≈ 200 miles in a family car” and mentions the derived 1.6 kg day-figure (BBC) |
| Le Monde (2011) lifecycle study | Finds 136 kg yr⁻¹ for a French employee – essentially the same as Berners-Lee’s 135 kg (Le Monde.fr) |
The arithmetic is straightforward:
- 4 g × 400 emails day⁻¹ = 1 600 g = 1.6 kg CO₂e day⁻¹
- 4 g × 33 750 emails yr⁻¹ ≈ 135 kg CO₂e yr⁻¹
Driving 200 miles in a modern UK petrol car (≈ 175 g CO₂ mile⁻¹) produces ~35 kg, but older cars emitted 600–700 g mile⁻¹, so the BBC comparison reflects a 2010-era family saloon (NimbleFins).
- Data-centre power-usage effectiveness (PUE) has fallen from ~2.0 to ~1.2 on average, and the grid mix has become less carbon-intensive.
- Berners-Lee’s 2020 revision gives a range of 0.03–26 g CO₂e depending on length, attachments and recipients – with a short laptop email now about 0.3 g (The Carbon Literacy Project).
- Independent blogs and LCA summaries echo the 0.2–0.4 g figure for minimalist mails and 17–50 g for image-heavy ones (The Carbon Literacy Project, Pawprint).
Robust market research shows the average office worker sends ~40 and receives ~120 emails per working day (Templafy). Even if we conservatively count every sent mail (40 × 0.3 g × 250 working days):
40 × 0.3 g × 250 ≈ 3 000 g ≈ 3 kg CO₂e yr⁻¹
Allowing for attachments and large CC lists might treble that, but we are still in the single-digit kilogram range, not 135 kg.
| Scenario | Emails / day | Emission per email | Daily CO₂e | Annual CO₂e |
|---|---|---|---|---|
| Berners-Lee (2010, heavy user) | 400 | 4 g | 1.6 kg | 135 kg |
| Typical 2025 office worker – plain text | 40 | 0.3 g | 12 g | 3 kg |
| Typical 2025 office worker – 10 % with attachments (17 g) | 40 ([email protected] g, 4@17 g) | – | 75 g | 19 kg |
| Very heavy modern user – 150 emails, half with small images | 150 | ∼1 g (blended) | 150 g | 37 kg |
Even the worst realistic 2025 case is still less than one-third of the 135 kg figure.
- Global email traffic was responsible for ≈ 150 Mt CO₂e in 2019 – just 0.3 % of world emissions (The Carbon Literacy Project).
- By contrast, UK passenger cars emitted ≈ 170 g mile⁻¹ in 2023; a single 200-mile journey therefore produces ≈ 35 kg CO₂e – already an order of magnitude bigger than a year of lean email use (NimbleFins).
- Historically accurate: If you adopt the 2010 4 g-per-email figure and you send several hundred messages a day, the maths works.
- Practically misleading today: Current evidence suggests most professionals emit one-or-two orders of magnitude less, because:
- per-email energy intensity has dropped 5to 20-fold, and
- realistic send-rates are far below 400 day⁻¹ for most users.
Verdict: The claim reflects an outdated worst-case scenario. It is useful for illustrating that digital actions aren’t free, but it no longer represents a typical business user in 2025.
- Cull your mailing lists and “reply-all” habits – every extra recipient multiplies impact (techsoup.ca).
- Send links, not large attachments; use shared drives where possible (Pawprint).
- Write concise, single-purpose messages – shorter compose/read times beat clever infrastructure gains (The Carbon Literacy Project).
- Archive and delete: data storage still consumes power over time – “dark data” is a hidden emitter (The Guardian).
Taken together, these steps cost nothing, reduce inbox stress, and keep even the modern, smaller email footprint heading in the right direction.
