Every page load physically moves electricity through the visitor’s device, the network, and the server that answered the request. That electricity has a carbon cost, and it scales with how much data moves and how long a CPU spends computing the response. This article explains what the badge in this site’s footer measures, what “carbon-negative” means when I use it, and how you can check any website yourself.
The two levers
Bytes and compute. A page under 60 kB transferred, with almost no client-side JavaScript, costs less to load than a typical WordPress theme that ships several megabytes of images, fonts, and framework code. Static hosting on renewable-powered infrastructure removes the second lever almost entirely: there is no server-side computation per request, just a file served from a cache.
Where the number comes from
The footer badge shows grams of CO2 equivalent per page view, and how the page compares with other pages tested. It is an estimate, not a meter. The estimate comes from the Sustainable Web Design Model, version 4, which converts the bytes a page transfers into energy across the data center, the network, and the visitor’s device, then multiplies by the average carbon intensity of the electricity grid. The model assumes a mix of first-time and returning visitors, because returning visitors load much of the page from their cache.
The host matters too. This site is served by Cloudflare, which is listed in The Green Web Foundation’s registry of green hosts, so the model counts the data center’s operational energy as renewable. The badge is rewritten with the measured numbers each time the site is built, so it does not drift from the page it describes.
Carbon-negative, specifically
I use “carbon-negative” to mean the footprint of my work is offset by more than its own weight. Every site I build is small and served from renewable energy infrastructure. On top of that, I plant 100 trees per client through One Tree Planted, and I fund water access for a family through charity:water. In the short term, that offsets my work’s footprint several times over.
Two caveats: the footprint is an estimate from a model, and offsets are not the same as not emitting. But 100 trees offsets several, several times more carbon than any variation from the estimate would range over. And my pages are small enough that they hardly need offsetting to begin with, unlike most WordPress sites.
Check it yourself
A claim like this is worth nothing unless something other than the person making it can check it. Website Carbon and Ecograder will measure any URL, including this one, and PageSpeed Insights will show how much data a page transfers. Run your own site through them and see for yourself where you stand.
Why a consultant would care
A lighter page is also a faster page, which helps visitors on slow connections and helps the page rank. The carbon figure is a side effect of doing the performance work properly, and some clients like having a number to point to. If, for whatever reason, the environment does not matter to you, the site performance still does for SEO and user experience reasons.