YouTube’s annual carbon footprint is about 10Mt CO2e (Million Metric tons of carbon dioxide equivalent), according to researchers — about the output of a city the size of Glasgow. But it doesn’t have to be that way, with a few easy design changes easily slashing that footprint by applying Sustainable Interaction Design.

A pair of researchers totted up the carbon footprint based on YouTube’s electric energy consumption from 2016, taking into consideration the entire chain of delivering an online video from servers to content-delivery networks to home routers. Web companies reporting carbon emissions will include datacentres, but miss the rest of the network — and for a streaming service such as YouTube, that’s where most of the energy is used, particularly with mobile networks.

“For us, it’s paramount to represent the delivery system — including the servers but also everything outside of the data centre, because that’s what in many cases contributes the most to energy consumption,” notes Daniel Schien, the paper’s co-author and a lecturer in computer science at the University of Bristol. “All of these videos result in a data volume being transferred from a server to the device you’re using, and how much data depends on the resolution of that video. If you know the resolution and duration of the video, you can calculate the data volume and that is what is important to estimate the energy consumption of the network.”

To help capture a fuller picture of YouTube’s footprint, the researchers built a model to not only capture that data but estimate it based on a range of end-user devices, since not everyone has the same phone, and not all phones are alike when it comes to energy consumption.

The aim is to let digital services — not just YouTube, but all others too — better understand their actual carbon footprint in order to see the impact that green design could have not just in their own systems, but the reduction caused across the wider networks if they cut their data use. “They are not directly responsible for this energy use — it is the direct responsibility of the internet service providers and the manufacturers of consumer devices — but design decisions in the services they use will affect the energy consumption across the system,” says Chris Preist, the other coauthor and a professor of sustainability and computer systems at the University of Bristol.

One design change the researchers do suggest for YouTube and other streaming services is eliminating the “digital waste” of showing video images to users who are only listening to audio — halting that could slash YouTube’s carbon footprint by up to 500kt CO2e each year, on par with about 30,000 homes. “In many cases, it would be possible to spot users are doing this and avoid the extra data being sent. For each user, this is not a large quantity, but given the vast number of YouTube users across the planet, the total mounts up.”

The aim wasn’t to point a finger at YouTube’s footprint, but to create a modelling toolkit to help websites and online services see how making different design decisions can cut their energy use. So far, the BBC and Guardian News are both in talks with the researchers; YouTube showed early interest, but nothing is as yet confirmed, Preist said. YouTube did not comment by the time of publishing, though it does already put plenty of effort into creating efficient video compression formats.

However, Preist notes there are caveats. “As with everything in the environmental space, the full story is more complicated,” he says. “With current network technologies, if you send less data along it, in most cases it doesn’t reduce the energy use. It’s like an airplane: if you don’t fly, the plane flies anyway, and so ‘not flying’ only reduces emissions if it leads to less airplanes flying in the long term. However, newer technologies, particularly in the mobile network, will mean that reduced data leads to reduced energy consumption more directly.”

While Preist and Schien’s modelling technique is new, the idea of Sustainable Interaction Design was first described in 2007 by Eli Bevis, but despite the rising environmental threats in decade since, building with sustainability in mind hasn’t become the norm with web design. Tim Frick is the author of Designing for Sustainabilityand works at digital agency Mightybytes, which since 2013 has run a website sustainability tool called Ecograder. Submit a URL, and Ecograder reports back a score based on features such as page speed and whether or not the hosting company uses renewable energy.

To Frick, every company — not only web giants like YouTube — should consider the impact of their corporate website on the environment, but also realise that the benefits of faster page load times and user accessibility can be good for business, too. “This translates directly to their bottom line and most businesses can relate to that,” he says.

Where to begin? Frick suggests optimising images, following accessibility guidelines and web standards, and streamlining user experiences, letting visitors get their tasks done with as few pages as possible or finding the right information quickly.

On the back end, he suggests looking for green hosting, using content delivery networks for faster downloads, minimising third-party software that slows down a site — such as ads but also fonts and other embedded technology — and using tools such as Google’s PageSpeed Insights to track your progress. “The advertising systems really are the worst,” he says. “When USA Today made their website GDPR-compliant by ditching visitor tracking software, they reduced page size by 90 per cent. More news sites should follow suit.”

And it is possible — Kris De Decker has proven it. He runs Low-Tech Magazine, a blog about renewable energy and green choices; one version of the site is run using servers entirely powered by solar energy. He slashed energy use ten-fold with a few simple design decisions: using default fonts, which don’t need to be downloaded; opting for dithering for image compression; refusing any tracking or advertising systems; and building a static website, like, as he says, “the old days.”

Most modern websites, WIRED UK included, are dynamic. “This means that every web page is generated anew every time a reader visits it, which requires constant computing from the server,” De Decker explains. “Visitors to a static website simply access ready-made documents on our server, which requires much less computing power. Any changes to our website only materialise every 24 hours, when the site is automatically regenerated.” Based on figures from the Chrome browser, the main page of Low-Tech was 2.9MB at the time of writing; the Guardian was 6.7MB; this website was 4.4MB — but the solar version of De Decker’s website was 376KB.

Not every website can live being updated once daily or showing only heavily compressed photos, but there are other changes modern websites could make. “I think that most of today’s websites show clearly that energy use is not considered at all,” he says. “Images are not compressed, videos are everywhere and start playing automatically, there’s pop-up boxes in every corner. There’s a tendency to use all the flashy innovations without much thinking. This is bad for energy use but also for user friendliness — not everyone has the fastest computer or internet connection.”

DeDecker isn’t the only one designing sustainable websites. Jack Lenox is a software engineer at VIP. “Working as a web developer I had ignorantly assumed that there was very little environmental impact from the work I did,” he says, but after attending a session about building a “planet-friendly web” at a Mozilla Festival, “this assumption was shattered.”

He started building a minimalist WordPress theme to try out the idea of sustainable design, eventually releasing “Susty”— which weighs in at a light-as-a-feather 6KB. But Lenox isn’t arguing all pages need be so lightweight. “I’m taking these things to an extreme,” he says. “With my theme I seek to raise awareness and highlight the point that we probably ought to be measuring websites in kilobytes rather than megabytes for many reasons, sustainability being just one of them.”

While most web designers aren’t thinking about energy use when they build a site, performance and loading times are key considerations for many. “There are teams at newspapers like the FT and the Guardian who are effectively dedicated to streamlining their web-based offerings,” Lenox says. “I admire sites like that of DotYork that packs typical conference stuff into pages that are about a quarter of the web’s median page size of about 1.8MB, while retaining an eye-catching design.” And change may be on the horizon, with Lenox pointing to the recent WordPress conference WordCamp Bordeaux, which had a specific focus on sustainability and ethics, as well as the launch of the Sustainable Web Manifesto.

Frick agrees. “When we first started doing this, we felt like we were the only ones,” he says. “Over time, we met others who were working on this as well. Now, there seems to be a growing movement of people around the globe who are interested in this work.”

That’s what Preist and Schien are hoping to encourage with their modelling tool, starting with video as the impact is potentially even more profound than with much smaller webpages. And because web companies haven’t considered sustainable interaction design before, even small changes made now could have a big impact, as De Decker notes: “That’s the positive side to this story: energy use has never been a theme in web design, so there’s a lot of so-called ‘low hanging fruit’ around.”