Sustainability / back-of-envelope

Your coffee, in carbon.

Four everyday things, measured the same way, in grams of CO₂-equivalent. Every figure is sourced below, and the flight is calculated in the open so you can check the arithmetic.

One AI prompt 0.03–1.1g A range, not a number. Why ↓

One email 0.3g Short, no attachment, written on a laptop.

One latte 550g Dairy milk, conventionally grown beans.

One flight 1.3t London–New York return, economy, one seat.

So how much is your habit?

I drink 3 coffees a week.

Drag to change

That is your coffee, for a year 86kg CO₂e

The same carbon as sending emails 286,000

…or sending AI prompts 75,000–2.9 million

As a share of one return flight to New York 6.6%

As a share of the average person's entire year — 6.6 t CO₂e 1.3%

Buy beans grown sustainably — shade-grown, less fertiliser, less water. Same drink, same milk. Drops a latte from 550 g to 330 g.³

For scale

One return flight is about 2,360 lattes — or 4.3 million emails.

← one latte is here0.3 px wide — this mark is already too big one flight →the whole bar

Drawn at a true linear scale, which is why the latte is invisible: at this width it measures 0.3 px. Showing the email at one pixel would need a bar about 1.1 kilometres wide. Comparisons like this are usually plotted on a log scale, which compresses the very difference being measured.

Where the numbers come from

AI prompt — 0.03 to 1.1 g CO₂e. A range, because the two best-documented figures disagree by 38×. Low end: Google, Measuring the environmental impact of delivering AI at Google Scale, August 2025 — median Gemini text prompt, 0.24 Wh, self-reported, not peer reviewed, and market-based (on a location-based basis the same prompt is 0.09 g). High end: Mistral's life-cycle assessment for Mistral Large 2, 1.14 g per 400-token query. Model training is outside both boundaries. Treat this row as an order of magnitude, not a measurement.
Email — 0.3 g CO₂e. Mike Berners-Lee, How Bad Are Bananas? The Carbon Footprint of Everything, 2020 edition. His range runs from 0.03 g for a spam email killed by a filter to 26 g for a long one with a big attachment. 0.3 g is his figure for a short email written on a laptop. Most of that is the electricity your own device burns while you write it, rather than transmission — which is why the figure is soft.
Coffee — 550 g, and 330 g grown sustainably. Carmen Nab and Mark Maslin, UCL, Geo: Geography and Environment, 2021. Their per-cup figures: black coffee 280 g, flat white 340 g, cappuccino 410 g, latte 550 g. Under sustainable production those fall to 130 g, 200 g and 330 g. Milk is most of a latte's footprint, so a smaller milky drink is a real reduction, not a rounding error.
Flight — 1.3 t CO₂e. Calculated here rather than quoted, so you can check it: London–New York is about 5,555 km each way, so 11,110 km return. UK DESNZ/DEFRA 2025 conversion factors put long-haul economy at 0.117 kg CO₂e per passenger-km, including radiative forcing. 11,110 × 0.117 = 1,300 kg. Strip out radiative forcing and it is nearer 0.9 t; add real routing and holding and it is nearer 1.4 t. There is no single agreed multiplier for the non-CO₂ warming effects of contrails, and that disagreement is worth more than the third significant figure.
The average person — 6.6 t CO₂e a year. UNEP Emissions Gap Report 2024, global average per-capita greenhouse gas emissions for 2023. Wealthy countries run around three times that.

Back-of-envelope, not a life-cycle assessment Compare real ESG reports →