typesafe.ai/blog/introducing-system-one-models-and-jev

The numbers

First visit

0.439 g CO₂e

Return visit

0.0075 g CO₂e

Hosting

unknown

LCP

588 ms

CLS

0.004

TTFB

18 ms

At 10,000 views a month this page emits about 39.7 kg CO₂e a year, roughly 163 km in an average petrol car. The estimate assumes 75% new and 25% returning visitors, a measured cache reload ratio of 2%, and world-average grid intensity. How we calculate this

1. Audit third-party servicessave ~0.151 g/visit (1.35 MB)High impact · moderate effort

   8 third-party domains account for 2.71 MB (92% of the page).

   Remove services that no longer earn their place; load the rest on interaction (facades for embeds, delayed consent-gated tags). Each third party is also a privacy and performance dependency.

   • f.vimeocdn.com1.75 MB
   • framerusercontent.com717 kB
   • i.vimeocdn.com121 kB
   • player.vimeo.com51 kB
   • fonts.gstatic.com48 kB
   • vimeo.com14 kB

   WSG 3.5: Treat third parties the same as first parties
2. Reduce JavaScript payloadsave ~0.061 g/visit (542 kB)High impact · moderate effort

   45 scripts total 2.17 MB on the wire (8.08 MB decoded). Bundles this size usually carry a lot of unused code.

   Split bundles per route, tree-shake dependencies, and audit with a bundle analyzer or coverage profile. A 25% cut is a conservative target for bundles this size.

   • player.module.js229 kB
   • player.module.js228 kB
   • player.module.js228 kB
   • player.module.js228 kB
   • player.module.js228 kB

   WSG 3.2: Minify and remove unused codeWSG 3.3: Modularize bandwidth-heavy components
3. Lazy-load below-the-fold mediasave ~0.0097 g/visit (87 kB)Medium impact · quick fix

   6 below-the-fold images/iframes (174 kB) download immediately for every visitor.

   Add loading="lazy" to below-fold img and iframe elements (and keep it off the LCP image). Browsers then fetch them only when scrolling approaches.

   • ih1bFwZGYJxlnijbTuXx3f9NeM.png96 kB
   • KEoJ6ZaJkOZG6mcjBsOlB3NCqek.png24 kB
   • z4Uu1YpJeEZPBSMTCMI0CN2PX0.png23 kB
   • 122749571110 kB
   • 122749573210 kB

   WSG 2.9: Optimize media to reduce resource use
4. Serve images at the size they displaysave ~0.0057 g/visit (51 kB)Medium impact · quick fix

   4 images are encoded at more than twice the pixels the layout shows, even accounting for this viewport's pixel density.

   Generate multiple sizes and let the browser pick with srcset/sizes; a 4000px original behind a 400px slot spends bandwidth no screen displays.

   • pvRPymJ0yRv5SHXNA3yDzieCZJk.webp102 kB
   • ih1bFwZGYJxlnijbTuXx3f9NeM.png96 kB
   • KEoJ6ZaJkOZG6mcjBsOlB3NCqek.png24 kB
   • z4Uu1YpJeEZPBSMTCMI0CN2PX0.png23 kB

   WSG 2.9: Optimize media to reduce resource use
5. Verify your hosting energyMedium impact · moderate effort

   This host has not published renewable energy evidence with the Green Web Foundation, so its energy source is unknown.

   Choose a provider listed in the Green Web Directory, or ask your current provider to publish evidence (and a carbon.txt). This cuts the data-center share of every single page view.

   • carbon.txtNo carbon.txt found at the site root; publishing one is the lightest first step.

   WSG 4.1: Use sustainable hosting
6. Stop downloading the same asset twicesave ~0.043 g/visit (380 kB)Advisory · quick fix

   12 assets were fetched more than once in a single page load (1.43 MB of repeated transfer).

   Usually a script injected twice or cache-busting query strings that differ per reference. Load each asset once and let the HTTP cache do its job.

   • oembed.json4 downloads · 4.3 kB
   • oembed.json4 downloads · 5.1 kB
   • oembed.json2 downloads · 2.2 kB
   • 12274957112 downloads · 20 kB
   • 12274957322 downloads · 20 kB

   WSG 3.2: Minify and remove unused code
7. Optimize web fontssave ~0.0080 g/visit (72 kB)Advisory · quick fix

   6 font files total 204 kB.

   Subset fonts to used glyphs, prefer one variable font over multiple weights, serve WOFF2 only, and consider system fonts for UI text.

   • 4w6Hg5DeDzuWT6PSthKEwbacV0g.woff259 kB
   • AjH8uNDZvXKC9xfhOZo8jIJKVss.woff251 kB
   • GrgcKwrN6d3Uz8EwcLHZxwEfC4.woff228 kB
   • 4iCr6K5wfMRRjxp0DA6-2CLnB4NHhg.woff225 kB
   • tDbY2o-flEEny0FZhsfKu5WU4zr3E_BX0PnT8RD8lqxTO…22 kB

   WSG 2.11: Use optimized web typography
8. Set a page-weight budgetAdvisory · moderate effort

   At 2.96 MB per view this page rates E. The findings above list where the weight is.

   Agree a transfer budget (e.g. under 975 kB reaches a B), enforce it in CI, and re-scan after each change to hold the line.

   WSG 3.1: Set goals based on performance and energy impact

Where the bytes are

• JavaScript2.17 MB · 45 req
• Images366 kB · 14 req
• Fonts204 kB · 6 req
• CSS123 kB · 5 req
• HTML82 kB · 6 req
• Data (XHR)12 kB · 10 req
• Data (fetch)4.1 kB · 5 req
• Other1.2 kB · 9 req