ICOS reduces the carbon footprint of its website while improving the site’s performance

31 October 2023
Jonathan Thiry

The average person surfing online might not realise it, but websites consume massive amounts of energy. To put this into perspective, it has been calculated that the internet consumes more electricity in a year than the entire United Kingdom. The more complex the website is, the more energy it uses.

Recently, the web developer team behind the ICOS website made several improvements on the performance of the page that not only improved its performance but also reduced the carbon footprint of the site. The footprint is calculated by a company called Website Carbon Calculator, which offers Website Carbon badges to websites to calculate and display their carbon emissions.

This initiative at ICOS was started by the Head of Carbon Portal, Alex Vermeulen, and executed by web developer Jonathan Thiry. We interviewed Jonathan to find out what exactly was made, and why other websites should follow suit.

- Thank you for this initiative! Where did you get the idea for this? 

First Alex and I wanted to add the Website Carbon badge to our data services, but then noticed that the performance of the website was not as good as it could be. I thought it would be best to have the badge everywhere so I started to look at what improvements I could make.  

- The badge shows ICOS homepage now being “cleaner than 75% of pages tested.” This is impressive! What is the biggest change that has been done with the website?  

The biggest switch was changing to responsive images. Now when a large picture is uploaded to the website, thumbnails of different sizes are automatically generated. These thumbnails are also created using the WebP format which often results in smaller files than JPEGs or PNGs. Then, the HTML pages contain links to all the versions of the image we want to display, and the web browser decides which one to one based on the window size and the screen pixel density.

Another change was reworking the homepage to use less JavaScript. The embedded Tweet is now a static image, and I’m working on a little module that would make it easy to create blocks that look like Tweets. The interactive map is now loaded only when clicking on it.

- Why should other websites do this? Or should they?

You should look at how your website performs. Even without talking about carbon emissions, these improvements make the website much faster and better to use. For example, the Head Office & Central Facilities page went from 2.78g CO2/view to 0.17g, a 16x reduction! The page loads faster, and many pictures look better than before because they are properly sized for your screen and don’t need to be adjusted by your browser anymore.

- How much CO2 does this save on a yearly basis? 

The carbon emissions reported by the Website Carbon Calculator are estimates per page view and it might be even more difficult to estimate the savings for a whole year*. I’ll take an example to simplify. We reduced the emissions of our homepage from 2.3g to 0.24g per unique page view. The page received about 57 000 unique views according to Google Analytics. This might have generated 131,1kg of CO2 last year and would be only 13,68kg today.


*The number calculated by Website Carbon Calculator is a rough estimate that does not take into account the mix of energy used in the surrounding data centre serving the pages. In the case of the Carbon Portal, which is in Lund, Sweden and the electricity mix in Sweden is at least 90% CO2-free which would make the ICOS website carbon emissions even lower.