thenewcuriosityshop.substack.com/p/the-essential-question

The numbers

First visit

0.320 g CO₂e

Return visit

0.029 g CO₂e

Hosting

verified green

LCP

928 ms

CLS

n/a

TTFB

15 ms

At 10,000 views a month this page emits about 29.7 kg CO₂e a year, roughly 122 km in an average petrol car. The estimate assumes 75% new and 25% returning visitors, a measured cache reload ratio of 9%, and world-average grid intensity. How we calculate this

1. Audit third-party servicessave ~0.120 g/visit (1.29 MB)High impact · moderate effort

   3 third-party domains account for 2.57 MB (97% 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.

   • substackcdn.com2.53 MB
   • fonts.gstatic.com38 kB
   • js.sentry-cdn.com2.8 kB

   WSG 3.5: Treat third parties the same as first parties
2. Reduce JavaScript payloadsave ~0.046 g/visit (491 kB)High impact · moderate effort

   138 scripts total 1.96 MB on the wire (6.25 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.

   • 27104.32466763.js214 kB
   • 97082.d14db6c3.js86 kB
   • 97605.96bfb060.js68 kB
   • 19311.3069a1e0.js59 kB
   • lib-react.09f9c904.js58 kB

   WSG 3.2: Minify and remove unused codeWSG 3.3: Modularize bandwidth-heavy components
3. Serve images at the size they displaysave ~0.012 g/visit (126 kB)Medium impact · quick fix

   3 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.

   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…251 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…59 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…53 kB

   WSG 2.9: Optimize media to reduce resource use
4. Fix caching for returning visitorssave ~0.0060 g/visit (49 kB)Medium impact · quick fix

   On a repeat visit 197 kB of static assets were re-downloaded instead of coming from cache.

   Serve static assets with Cache-Control: public, max-age=31536000, immutable and versioned filenames so returning visitors download almost nothing.

   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…Cache-Control: public, max-age=31536000 · 159 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…Cache-Control: public, max-age=31536000 · 38 kB
   • https%3A%2F%2Fsubstack.com%2Fimg%2Favatars%2F…Cache-Control: public, max-age=0 · 397 B

   WSG 4.2: Optimize caching and support offline access
5. Lazy-load below-the-fold mediasave ~0.0056 g/visit (60 kB)Medium impact · quick fix

   7 below-the-fold images/iframes (119 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.

   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…59 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…53 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…2.5 kB
   • https%3A%2F%2Fbucketeer-e05bbc84-baa3-437e-95…1.2 kB
   • https%3A%2F%2Fsubstack-post-media.s3.amazonaw…1.2 kB

   WSG 2.9: Optimize media to reduce resource use
6. Remove references to broken resourcessave ~<0.001 g/visit (1.6 kB)Advisory · quick fix

   1 request answered 4xx/5xx on load: transfer and connections spent on nothing, on every single visit.

   Delete or fix the references (stale asset URLs, dead third-party tags). Each one is a request the page provably does not need.

   • flowsHTTP 401 · 1.6 kB

   WSG 4.4: Setup necessary error pages and redirection links
7. Set a page-weight budgetAdvisory · moderate effort

   At 2.64 MB per view this page rates D. 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

• JavaScript1.96 MB · 138 req
• Images374 kB · 10 req
• CSS220 kB · 23 req
• Fonts38 kB · 1 req
• HTML37 kB · 2 req
• Data (XHR)9.5 kB · 4 req
• Data (fetch)2.6 kB · 2 req