The footprint of sending a file is dominated by something almost nobody looks at: how long it is stored afterwards. The transfer is over in minutes; storage runs every second the file exists. So choosing a genuinely low-carbon service comes down to three questions — what powers the data centre, how long files are kept, and whether the provider shows you evidence instead of a leaf.
That is the whole method. The rest of this page is how to apply it without being fooled.
Where the energy actually goes
Three costs, and they are nowhere near equal.
Sending the file uses networking equipment for the minutes the transfer takes. Real, and small.
Storing the file uses energy continuously — drives powered, plus the cooling that keeps them at temperature — for as long as the file exists. A file kept for a year spends hundreds of thousands of times longer being stored than it spent being sent.
Copying the file multiplies storage. A service keeping three copies in three regions has tripled the continuous cost, and many large providers do exactly that by default, for good durability reasons.
The consequence is the single most useful thing on this page: a service that deletes your file after a week can have a smaller footprint per file than one keeping it forever on renewable power. Duration multiplies everything, including the clean version.
That does not make short retention always right — there are good reasons to keep client work. It does mean a provider boasting about renewables while keeping everything indefinitely has optimised the smaller variable.
The three questions to ask
1. What actually powers the data centre?
Three different claims hide behind the same word:
- Renewable supply — the facility runs on renewable electricity, ideally under a named supply arrangement.
- Renewable-matched — the provider buys certificates equal to its use, generated elsewhere and at other times.
- Offset — the provider emits, then pays for reductions somewhere else. The weakest of the three, and often the loudest.
None of these is fraud. They are different claims, and marketing routinely presents the third as if it were the first. How to tell which one you are being sold.
2. What happens to a file nobody downloads?
If the answer is "we keep it until you delete it", the provider's footprint grows with every customer, and yours grows with every file you forget. A service with expiry built in is doing the largest available piece of work on your behalf.
3. Is there anything you can check?
A serious claim is falsifiable: a named facility, a country, a published efficiency figure, a certification with a registry you can search. "Powered by green energy" with none of those is not a claim you can weigh.
What matters less than you think
Compression. A file made 20% smaller costs 20% less to send and store. Deleting it costs 100% less. Compress when it is free; it is not the lever.
Efficiency ratings. Differences between modern data centres are real, but small next to how many copies exist and for how long.
Which European country. Grid carbon intensity really does vary by country. It is still second-order next to duration and replication.
The lever that is actually yours
Delete things. Most of what any of us stores is never opened again — that is the whole argument, and it is the only step here that is both large and entirely within your control. Cull before you upload, stop archiving every version, and give working files a shorter life than deliverables.
Where Yungle stands
I run Yungle, so read the checkable parts and discount my adjectives.
- Hosted at Hetzner in Germany, on hydropower. The data centre's efficiency figure is a PUE of 1.13, and it holds ISO 27001 and EMAS certification — those are Hetzner's numbers and certificates, not mine.
- One primary copy, not three regional replicas, plus nightly backups in EU-jurisdiction storage at a second provider. An efficiency choice, and equally an availability trade I would rather state than hide.
- Free transfers expire after 7 days. Paid collections keep files as long as you like, which people ask for and which is worse on this measure. Both are true.
- A tenth of the profit goes to Rainforest Trust. That is a donation, not a claim about electricity.
The argument against treating this as a climate decision at all: a small service's footprint is not where anyone's emissions live. Choosing carefully here is a five-minute refusal to fund the alternative, not a material cut. Flights, heating and how often you replace hardware are where the material version is. What we claim, and what we don't, is written down in one place.
In short
Ask what powers it, ask how long files are kept, ask for something you can check. Then delete more than you think you need to — that part is yours, and it is the part that works.