Sustainable digital services: 15 measures for a smaller CO₂ footprint

In Brief

• The ICT sector causes at least 1.7% of global greenhouse gas emissions – roughly on par with aviation.

• Sustainable websites are faster websites: energy efficiency and performance go hand in hand.

• 15 concrete measures from architecture, frontend and operations measurably reduce the digital footprint.

• Sustainability encompasses three dimensions: ecology, economics and social accessibility.

• Even simple steps such as consistent caching or optimised image formats save considerable amounts of data over time.

Servers and Mobile Phones Running Hot

The digital transformation offers enormous opportunities. Yet at the same time, its energy demand continues to rise unchecked. Many discussions revolve around AI and productivity – while the ecological impact of global IT infrastructure continues to be underestimated by many. Studies estimate the ICT sector's share of global greenhouse gas emissions at a minimum of 1.7%. The aviation industry, often criticised for its emissions, accounts for around 2% globally – placing the ICT sector in a similar order of magnitude. At the same time, figures in the digital space are only very limitedly measurable. The last comprehensive estimates predate the AI boom, meaning today's energy demand is likely significantly higher than the available figures suggest.

Websites are also becoming increasingly data-intensive: the median mobile website stood at 960 KB in 2016, rose to 1,885 KB in 2020, and had already reached around 2,666 KB by April 2026. Larger websites require more data transfer. They place greater strain on end devices and infrastructure. And they lead to longer loading times.

This becomes particularly relevant where network infrastructure is less developed or devices are older. Sustainability therefore also means designing digital services to function as efficiently and resource-consciously as possible – regardless of device or location.

Making the Invisible Energy Consumption Visible

Tools such as Website Carbon attempt to calculate a website's CO₂ emissions based on the data it transfers. The results are approximations – but they create awareness.

One example: the page you are currently viewing achieves a B rating, is "cleaner" than 83% of all tested websites, and generates around 0.09 g of CO₂ per visit. This indicates that optimisation potential exists – and that even small improvements have a measurable impact.

A key lever lies in the choice of hosting provider. Many data centres continue to be powered by non-renewable energy. Sustainably operated infrastructure is therefore a powerful tool for reducing the ecological footprint of digital services.

However, hosting is only part of the equation. Energy is also required for the transmission and rendering of content. Those who develop or operate digital services have numerous opportunities to actively reduce consumption.

As developers: our shared responsibility for the digital carbon footprint

As developers, we find ourselves in a dilemma. On one hand, we want to create inspiring products for our clients, help them open up markets and sell products in innovative ways. On the other hand, we cannot avoid seeing ourselves as co-contributors to an ever-growing global challenge. The science is clear: sustainability can only be achieved through shared responsibility and consistent action.

15 Measures for Sustainable Digital Services

Sustainability does not begin with hosting alone. Energy can also be saved and performance improved in design, architecture, frontend and backend development.

One important principle: sustainable websites are generally also faster websites. They offer a better user experience, have a positive impact on Core Web Vitals, and thereby improve visibility in search engines and AI-based answer systems.

Here are the 15 most important areas where we as developers can take action to optimise the delivery and display of digital services and products, and thus save energy:

• Use modern transfer protocols and Content Delivery Networks (CDN): Modern CDNs today deliver web content via HTTP/3 as standard, which is supported by all major browsers and providers such as Cloudflare, Fastly and Akamai. Compared to HTTP/2, HTTP/3 enables faster loading times – particularly on mobile and unstable networks (around 8% on desktop and 3.5% on mobile). The most important lever here lies not in frontend code, but in choosing a contemporary infrastructure. By delivering content from geographically close locations, loading times, repeat transmissions and thus energy consumption per page visit are reduced.

• Use modern compression methods (Brotli, Gzip, Zstandard): Compressing text resources such as HTML, CSS and JavaScript remains a key lever for reducing the amount of data transferred. Alongside Gzip and the more efficient Brotli, Zstandard (zstd) is increasingly gaining traction – it operates at a comparable compression rate but significantly faster than Brotli, and has been supported by CDNs such as Cloudflare since 2025. Browser support is well advanced, with only Safari currently lacking native support. Regardless of the method used, it is advisable to statically compress assets during the build process to avoid additional computational load on the web server and save energy.

• Use server-side rendering with an intelligent caching strategy: With server-side rendering (SSR), pages are generated as HTML on the server and delivered to the browser, thereby reducing the load on end devices. Modern developments such as Partial Hydration, Islands Architecture or React Server Components further reduce the amount of JavaScript required, as only interactive components are delivered. Combined with an upstream caching system or static delivery via a CDN, a page does not need to be re-rendered on every visit.

• Think carefully about code splitting: Even with modern transfer protocols such as HTTP/3, code splitting remains relevant. Its primary benefit lies in reducing the amount of JavaScript that needs to be executed initially. When only the code required for the currently displayed view is loaded, the parsing, compilation and execution work in the browser is reduced. This has a positive effect on loading time, interactivity and energy consumption on the end device.

• Set long-lived cache headers: The longer static assets such as JavaScript, CSS or images can remain in the browser cache, the fewer requests and data transfers are needed. Established best practices such as content hashing in file names make it possible to safely use very long cache durations, as files automatically reload when they change. In addition, immutable headers (Cache-Control: immutable) ensure that unchanged assets are not re-requested at all. This reduces network load, speeds up page visits and lowers energy consumption on both server and client side.

• Use lazy loading and Intersection Observer: Resources should only be loaded and executed when they are actually needed. For images and iframes, this can most easily be achieved today using native lazy loading, which is supported by all common browsers. In addition, the Intersection Observer API makes it possible to start – or deliberately pause – computationally intensive actions such as animations, videos or JavaScript logic only when content enters the visible area. Modern browser features such as content-visibility: auto go a step further by skipping rendering and layout calculations for content that is not visible.

• Optimise images with responsive images and automated delivery: Images are one of the biggest drivers of data volume on the web and should be consistently optimised. Responsive images ensure that end devices only load the image sizes they actually need, while modern formats such as AVIF (around 95% browser support in 2026) significantly reduce file sizes compared to JPEG or WebP. Current web performance guidelines recommend automating image optimisation through build processes or image CDNs rather than doing it manually, in order to always deliver the most efficient variant for each browser and device.

• Provide a dark mode: Dark mode divides opinion. Some people love it, while others find reading light text on a dark background uncomfortable. What is certain is that dark mode has a positive effect on energy consumption for OLED screens: real-world tests showed between 7–9% lower consumption during typical use. This effect does not apply to LED screens.

• Prevent reflows: Not every reflow results in a layout shift visible to users, but it does cause additional computational work in the browser. Modern browsers now automatically mitigate many issues, such as pre-reserving space for images and media. Nevertheless, avoidable reflows frequently occur due to dynamically loaded content, JavaScript-based layout changes or complex animations. On mobile devices in particular, this can consume a noticeable amount of energy.

• Use service workers: Service workers make it possible to store resources and content in a controlled cache, thereby avoiding repeated network requests. The greatest benefit arises with web apps or progressive web apps, particularly when these need to be usable offline or are used on a regular basis. In such cases, loading times, network usage and repeated parsing and compilation work can be significantly reduced.

• Build a design system: A design system helps to centrally define and consistently apply reusable components, layouts and styles. This avoids redundant code, duplicate assets and inconsistent implementations that negatively affect performance and maintainability. At the same time, a solid design system makes it easier to maintain performance, accessibility and sustainability standards across all pages.

• Reduce third-party scripts: Third-party scripts (analytics, ads, social media widgets, chat tools) are often the biggest energy consumers on a page. They generate additional network requests, CPU work on the end device, and frequently run in the background independently of user behaviour. Regular audits are therefore all the more important to assess which scripts actually provide value and which are dispensable. Where possible, third-party functions should be loaded with a time delay, loaded conditionally, or replaced with lighter alternatives.

• Use the Speculation Rules API for intelligent prefetching: The Speculation Rules API makes it possible to preload or even fully pre-render future page navigations in the background. Users experience near-instant page transitions as a result, meaning less waiting time and therefore less active device time. This is currently supported primarily by Chromium-based browsers.

• Optimise fonts: There is also significant potential when it comes to fonts. By using the WOFF2 format – which is 30% smaller than WOFF thanks to Brotli compression – subsetting to only the character sets actually needed, and using variable fonts, file sizes can be reduced by 80–95%. Anyone who does not need to convey specific branding through fonts can avoid additional downloads entirely by using a system font stack.

• Embed videos efficiently: Videos are the largest consumers of data on the web and deserve special attention. Autoplay should be avoided, or at least restricted to muted playback when visible. For embedded YouTube or Vimeo videos, the facade pattern is recommended: instead of immediately loading the full iframe – YouTube's embed alone brings over 500 KB of scripts – only a static preview image is initially displayed. The actual player loads only on click. Web components such as lite-youtube-embed make this easy to implement and improve the Largest Contentful Paint by 500–800 milliseconds.

This list is not exhaustive. At a technical level, the Carbon Aware Computing approach goes one step further: computationally intensive tasks such as builds, imports or batch processes are deliberately shifted to time periods or regions with a high proportion of renewable energy. The Carbon Aware SDK from the Green Software Foundation provides concrete tools for operating digital services not only efficiently, but also in a climate-conscious manner in terms of time and geography.

Sustainability does not end with technical delivery – it also encompasses how digital services are used and what downstream processes they trigger. In the field of e-commerce in particular, clever user guidance and subtle prompts can encourage more sustainable decisions: for example, by informing customers that additional delivery attempts or express deliveries consume more energy.

Sustainability is Multidimensional

Sustainability encompasses far more than ecological factors. It also concerns economic and social responsibility. We should therefore design digital services so that they are:

• efficient and resource-conscious (ecology),

• cost-efficient to operate and further develop (economics),

• accessible to all people – regardless of device, ability or infrastructure (society).

Sustainable digital value creation only emerges when all three dimensions are taken into account.

Small Optimisations, Big CO₂ Impact

Often the greatest effect comes from many small optimisations. Even switching to modern image CDNs or consistently applying caching strategies can save considerable amounts of data – and thus CO₂ – over the course of months.

Sustainability as a Quality Feature – Act Now

Companies bear a decisive responsibility towards the environment, the economy and society. Digital services are no longer a peripheral factor – the way they are designed has real-world consequences.

Sustainability should today be consciously integrated as a quality feature in the planning of websites, applications and digital ecosystems. Efficient, performant and resource-conscious solutions make ecological sense. They improve the user experience and secure long-term competitiveness.

Would you like to know where your digital platform stands today? We will analyse the biggest levers for a more sustainable and higher-performing implementation together – get in touch with us.

Contact for your Digital Solution

projektanfragen.ch@unic.com+41 31 560 16 16

Book an appointment

Are you keen to talk about your next project? We will be happy exchange ideas with you.

Contact for your Digital Solution with Unic

projektanfragen.de@unic.com+49 89 43 77 80 90

Book an appointment

Are you keen too discuss your digital tasks with us? We would be happy to exchange ideas with you.