Digital carbon ratings in practice
Carbon emissions ratings across the Wagtail ecosystem
Don’t we all love a nice little metric to use as a target! Take our website homepage for example: we recently hit a "100" perfect score in Google Lighthouse, across all categories!
We truly try hard to make our site as fast and as accessible as possible. However although those numbers are lovely news, they still only say so much: a lot of websites can meet those "perfect" scores. And the scores miss out on a lot of aspects of the website’s impact.
One such aspect is the website’s carbon footprint. In particular, how carbon-intensive it is to load the website’s pages. Enter Digital Carbon Ratings!
How the ratings work
The ratings scale was put together based on websites’ page weights – specifically how they are distributed in the HTTP Archive dataset:
- A+: 272.51 kb (top 5%)
- A: 531.15 (next 5%)
- B: 975.85 (next 10%)
- C: 1410.39 (next 10%)
- D: 1875.01 (next 10%)
- E: 2419.56 (next 10%)
- F: ≥ 2419.57 (bottom 50%)
Those page weight numbers are then used to estimate the carbon footprint of the pages via the Sustainable Web Design (SWD) model, version 4. Page weight is only an approximation of websites’ energy consumption, but it does have the big advantage of being usable across all aspects of building and loading the page: server-side, in transit over the network, and also on users’ devices. In the SWD model, 54% of sites’ emissions are estimated to be with user devices, not servers!
Results for Wagtail
This methodology is very interesting for Wagtail, because it means we get to compare how Wagtail websites score with all websites across the web:
Here are our results:
- A+: 3.4% of sites (5% for the web)
- A: 8.9% (vs. 5%)
- B: 16.5% (vs. 10%)
- C: 13.2% (vs. 10%)
- D: 16.8% (vs. 10%)
- E: 9% (vs. 10%)
- F: 32.2% (vs. 50%)
This means Wagtail scores worse than the "web average" for A+ and E categories, but much better everywhere else. Wagtail sites can definitely be optimized to be as lightweight as possible, so we’re definitely gunning for better results than average across the board! And page weights of Wagtail sites compare well with other CMS sites specifically:
This is comparing Wagtail with WordPress, Drupal, Umbraco, and the "all" websites data, per the HTTP Archive Tech Report. 🤫 we regularly review and report on industry trends like this. If you want to see more of this, do subscribe to our newsletter.
Pitfalls
Ratings show promise in simplifying this type of comparison and generally making this information more accessible. However there are clear pitfalls that are tricky to navigate once you want to rate and actively compare many sites:
- The ratings use the SWD model version 4 only. A lot of online carbon calculators still only use version 3, which would overestimate carbon emissions.
- The industry overall trends towards heavier page weights, while the ratings are fixed on 2023. If the ratings don’t update then all scores will degrade over time for sites that don’t track those numbers. If the ratings were to update, they wouldn’t be as comparable anymore!
- "F" ratings are much more frequent, on purpose. This increases the prestige of higher ratings, but does mean for comparisons like ours, it looks very surprising that so many sites are rated "F"! Until you realise we are 18% below the expected number of sites.
There are also a few growing pains to solve with the system – it’s not well documented how the ratings’ underlying page weights were estimated, which would be important to get the most correct scoring of a site.
What to do
Try out the ratings and see how it feels! It’s really simple as it’s based on page weight. Share your sites’ ratings with colleagues and ask them what they think of it. For Wagtail, we’re happy to report we got a rating of “A” for our homepage 🎉.
We’ll be chasing that A+! For a better sense of our direction, check out Open Source Carbon Footprints shownotes.
