Website carbon audit

If you've been following us for a while you will know that we've looked at the CO2 emissions from council homepages, from university homepages, and from UK government organisations and tried to encourage organisations to do better. We don't just tell other people to do better - we constantly strive to reduce the CO2 impact of our own website by optimising pages, images, and code too. Up to now we've had a fairly ad-hoc approach to checking individual page emissions using the Website Carbon Calculator. But it was time to do a more thorough audit to get the big picture.

The first step is knowing how many views each of our pages have had. We started recording privacy-first web analytics in January 2021 and this gives us daily page views for each page across, the Data Mapper, and various Github-pages-hosted projects that we have.

Next we needed to use the Website Carbon Calculator to estimate CO2 emissions for each page. We have a huge number of pages spread across multiple projects so it wasn't feasable to run them all through Website Carbon Calculator. Instead we've processed the most popular pages - these account for more than 80% of all our page views. For the remaining page views we just used the average CO2 emissions from the other pages.

The final step was to multiply each pages views by its CO2 emissions and add it all up. That gives us a grand total of almost 43kg of CO2 since 1st January 2021. That works out equivalent to around 600 cups of tea (with milk) or 1.3 cups of tea (with milk) per day. Not bad!

In doing this audit we've already found some specific pages that are much bigger than we'd like - mostly been down to un-optimised images - so we've already taken steps to improve them. How would your website do?