On mobile, half of all home pages now weigh more than 2.3 megabytes. I don’t believe we will achieve digital sobriety by making internet users feel guilty. It is mostly decided upstream, in a few technical choices that are made only once: page caching, the format and size of images, how videos are encoded and hosted, and the choice of host. I explain them using my own website as an example.
79% of the digital footprint comes from our devices
Internet users are often asked to sort their emails or watch fewer videos, and in The Fantasy of Digital Ecology I explained why making each person feel guilty diverts attention from industrial choices, whose effects are far greater. During the first session of the webinar series I led in October 2025 for the Fondation Afnic, I said so about artificial intelligence: users should not be made to feel guilty, and the responsibility lies with the industrial firms that build gigantic data centres connected to the drinking-water supply.
For a website, the place to start is the figures. According to the study carried out by Ademe and Arcep on 2020 data, digital technology accounts for 2.5% of France’s carbon footprint; devices (phones, computers, screens, televisions) account for 79% of it, against 16% for data centres and 5% for networks, and 78% of this footprint comes from manufacturing the equipment. So it seems to me that, when you make a website, the most useful thing you can do for sobriety is to make it light, so that it can be read on an old phone or over a slow connection, and nobody has to change their device to read it. Yet pages keep getting heavier: according to HTTP Archive’s Web Almanac, the median weight of a mobile home page went from 845 kilobytes in 2015 to more than 2.3 megabytes in 2025, and images are what weighs the most.
During the second session, a participant asked me how I reconciled sobriety with a dynamic website, where the server runs a program and queries a database on every visit. I answered in two parts: first the choice of software and its settings, then the choice of host. For the software, part of the answer lies in caching, which means calculating a page only once and sending it back as it is on every visit as long as nothing has changed, as I explain in Site statique, site dynamique, CMS : une base de données, des gabarits et un moteur derrière chaque page.
All the images on my website switched to WebP
The other part of the answer has to do with images. I decided to stop using the JPEG format for the images on my website and to switch to WebP. I changed a setting in SPIP, all the images were regenerated in one go in this format, and since then pages have been lighter and load faster. When you measure the page of my article Data Centers : We Fill Them Ourselves, you can see what this means in practice: the opening photograph is displayed a little under 1,000 pixels wide, SPIP has recalculated it as a 1,110-pixel WebP, and it weighs 58 kilobytes. It calculated it only once, and serves it again on every visit, because my website’s templates call its image filters (resize, crop, convert). The whole page weighs a little over half a megabyte when it opens, and the heaviest part is the fonts, more than 200 kilobytes, far more than the photograph. This is one of the reasons why I consider SPIP the most resource-efficient of the CMSs I know, and Drupal is also well designed in this respect.
Google, which introduced WebP in September 2010, states that lossy-compressed WebP images are 25 to 34% smaller than JPEGs of equivalent quality. Safari has displayed it since September 2020, and every common browser along with it. And on a website made with WordPress, like more than 40% of the world’s websites? WebP images can be uploaded there since version 5.8, in 2021, but photographs uploaded as JPEG are converted only with a plugin, for example Modern Image Formats, offered by the WordPress performance team.
Without a CMS, this work has to be done by hand, resizing each photograph before putting it online: one that comes off a phone is several thousand pixels wide, to be displayed on a few hundred. And it is the text written for an image (its alternative text, its caption, its file name) that makes it findable and accessible; that is the subject of Une image n’existe sur le web que par le texte qu’on écrit pour elle : alt, légende, transcription, sous-titres.
One minute of video, ten to twenty megabytes
Video is by far the heaviest thing on a website. In 2018, in Create lightweight, high-quality video files, I described step by step the method I use. In it I distinguish two files: the master, the original in the best possible quality, which you keep in two copies on two different media, and the distribution file, encoded for a specific use. For the web, I make this second file with HandBrake, because no editing software, in my view, can export a file that is both light and of good quality; HandBrake is free, open-source software, developed since 2003, which runs on Windows, macOS and Linux.
In Best practices for putting videos online, I give the settings for the web: the MPEG-4 H.264 format, which every browser can play, the “Web Optimized” box ticked in HandBrake, so that playback can start before the download is complete, and a file that weighs between ten and twenty megabytes per minute, which works almost everywhere. In the first article, I pointed out that a resolution of 1280 × 720 pixels is enough for a screening in a cinema, so that the same file can serve both purposes. I recommend watching the encoded video all the way through before putting it online, because that is exactly what the people who play it will see.
The video player whose code I give in the same article includes two settings that help with sobriety. With the preload="none" attribute, the browser downloads nothing of the video until the person has started it, and a still image, set by the poster attribute, is displayed in its place in the meantime.
When you host your videos with your website rather than on a platform, they are backed up every time you back up the site. And when you have encoded them yourself, you know exactly what you have put online. When you put a video on YouTube, you hand over your original file, but you don’t know whether it is kept; you know there are several encodings, and for everything else you are completely in the dark.
A data centre in the basement of a Geneva housing cooperative
That leaves the choice of host. During that session, I mentioned the Swiss host Infomaniak, founded in Geneva in 1994 and owned by some of its employees. Its latest data centre is in Geneva, in the basement of La Bistoquette, a housing cooperative. The first servers were brought into service there in December 2023, and since 11 November 2024 all the electricity they consume has been recovered as heat in the neighbourhood’s district heating network, run by the Services industriels de Genève. At its inauguration, on 27 January 2025, the centre was running at a quarter of its capacity; at full load, around 2028, it is expected to heat the equivalent of 6,000 homes all year round. The servers are cooled there without air conditioning and without additional water, and the building uses very little electricity on top of what the servers use: its PUE (the ratio between the electricity used by the whole building and that used by the machines alone) is 1.09, against a European average of 1.64 according to the press release from the Services industriels de Genève. In Data Centers : We Fill Them Ourselves, I set it alongside three other very different data centres, to show that their effect on a territory depends on who owns them and on the computations run in them.
According to the International Energy Agency, data centres consumed around 415 terawatt-hours in 2024, or 1.5% of the world’s electricity, and this consumption could more than double by 2030. The historian Fanny Lopez, in À bout de flux (Divergences, 2022), shows that digital technology rests on an electrical infrastructure we do not see, and that data centres draw on public grids without producing any electricity themselves; she proposes turning electricity networks into commons, combining the national grid, taken back in hand by its users, with local networks comparable to renewable energy cooperatives. By choosing its host, an association can have a say, on its own scale, in what becomes of this electricity and this heat.
You can go much further. Since autumn 2018, the website of Low-tech Magazine, Kris De Decker’s online magazine, has run on a small computer installed on the balcony of his home in Barcelona and powered by a solar panel (50 watts at first, 30 today). Its images are dithered in black and white with four levels of grey to weigh less, a page weighs on average less than half a megabyte, about five times less than on the old site, and the site goes offline when the battery is empty, which happens during long spells of cloudy weather. I do not suggest this solution to associations, which need a website that is always reachable, but I find it illuminating: it shows that a website’s sobriety is decided in its infrastructure, and that it can come at the price of a site that is sometimes offline, which you may or may not choose to accept.
Five checks to make with the person who looks after the website
None of this happens by itself: with a well-designed CMS you can still serve images that are far too heavy if the templates were written without thinking about it, and a host that cares about the environment also hosts websites weighing several megabytes per page. I suggest checking five points with the person who looks after the website:
- Measure the weight of a typical page in the browser’s developer tools (right-click on the page, “Inspect”, “Network” tab), reloading the page.
- Look at the format and size of the images, so that they are close to their display size and in a recent format such as WebP.
- Check that caching is enabled and configured, in the CMS or at the host.
- Make sure that videos are encoded for the web, hosted with the website, and loaded only when someone starts them.
- Read what the host publishes about where its electricity comes from, how long it keeps its servers and what it does with their heat.
A light website also displays faster on slow networks and old devices, and stays readable for people who don’t have the latest phone. In Web seminar resources : « better communication on the web », I presented accessibility as the common thread of this series, and economic accessibility, regarding the cost of tools, as one of its forms; a light website is another. By choosing a host and software, you also decide who you entrust your data to, a question I address in Nom de domaine, hébergeur, plateforme en ligne : à qui appartient le site de votre association ?.
