People who move to a green host are sometimes surprised that their carbon estimate only drops a little. That isn't a mistake. The data centre is only one of the places energy is used when someone views a page; the network and the visitor's own device use energy too, and a green host doesn't change those.
Where the 18% comes from
GreenTracer uses the Sustainable Web Design Model v4. It estimates energy per gigabyte transferred in three segments (data centres, networks and user devices), each with an operational part (electricity used while serving the page) and an embodied part (the emissions from making the equipment). In total that comes to 0.300 kWh per gigabyte, of which the data centre's operational electricity is 0.055 kWh.
When the host is confirmed as green, the model treats that data-centre operational electricity as renewable and removes its emissions. Everything else stays. At the global average grid intensity the model uses (494 g CO₂e per kWh), that means:
- about 0.148 g CO₂e per megabyte per page view on a host that isn't confirmed as green;
- about 0.121 g CO₂e per megabyte on a host that is, roughly 18% lower.
A 2 MB page goes from about 0.30 g to about 0.24 g per view on a green host, a saving of about 0.05 g. Making the same page 1 MB lighter saves 0.12 to 0.15 g per view, more than twice as much, wherever it is hosted.
What the green hosting check means
GreenTracer asks the Green Web Foundation whether the site's host is in its dataset of verified green hosting providers. Hosting organisations submit their own information and evidence, which the foundation reviews. A “listed as green” result means the host is in that dataset. It isn't a certificate for your particular site, and the foundation itself provides the data “as is”, noting that errors are possible. That is why GreenTracer reports say a host is “listed as green by The Green Web Foundation”, or that green hosting “could not be confirmed”, rather than calling a website green. The check is repeated: a result older than 90 days is shown as “not confirmed” until it has been checked again. Our article on green hosting proof without greenwashing covers what evidence to ask your host for.
If your host isn't listed
- Check your domain with the Green Web Check. A content delivery network or proxy in front of your site can mean the check sees that provider rather than your host.
- Ask your host whether they have submitted evidence through the foundation's verification process, and what they can show about their electricity. The foundation explains what it accepts as evidence.
- If you're choosing a new host, the hosting directory lists verified providers.
Do both
Green hosting and a lighter page work on different parts of the estimate, so they add up. Hosting is often a one-off decision; page weight is something you can improve this week, and it also makes the site faster for every visitor. Start with the heaviest files, usually images, then fonts and third-party scripts.
Check your page: the report shows the hosting result and the estimate side by side, and “How we estimated this” shows the calculation.
