www.harvard.edu

The numbers

First visit

0.491 g CO₂e

Return visit

0.0051 g CO₂e

Hosting

unknown

LCP

412 ms

CLS

0.003

TTFB

7 ms

At 10,000 views a month this page emits about 44.4 kg CO₂e a year, roughly 182 km in an average petrol car. The estimate assumes 75% new and 25% returning visitors, a measured cache reload ratio of 1%, and world-average grid intensity. How we calculate this

1. Lazy-load below-the-fold mediasave ~0.092 g/visit (824 kB)High impact · quick fix

   17 below-the-fold images/iframes (1.65 MB) 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.

   • kidneys.png397 kB
   • brain2.png374 kB
   • heart.png300 kB
   • uterus2.png227 kB
   • liver.png136 kB

   WSG 2.9: Optimize media to reduce resource use
2. Serve images at the size they displaysave ~0.065 g/visit (583 kB)High impact · quick fix

   11 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.

   • kidneys.png397 kB
   • brain2.png374 kB
   • heart.png300 kB
   • uterus2.png227 kB
   • liver.png136 kB

   WSG 2.9: Optimize media to reduce resource use
3. Audit third-party servicessave ~0.042 g/visit (374 kB)High impact · moderate effort

   17 third-party domains account for 749 kB (23% 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.

   • www.googletagmanager.com311 kB
   • connect.facebook.net154 kB
   • www.google.com145 kB
   • cse.google.com49 kB
   • pagead2.googlesyndication.com23 kB
   • www.google-analytics.com22 kB

   WSG 3.5: Treat third parties the same as first parties
4. Reduce JavaScript payloadsave ~0.027 g/visit (239 kB)High impact · moderate effort

   21 scripts total 955 kB on the wire (3.04 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.

   • vendor.min.js165 kB
   • js163 kB
   • gtm.js148 kB
   • cse_element__en.js129 kB
   • fbevents.js110 kB

   WSG 3.2: Minify and remove unused codeWSG 3.3: Modularize bandwidth-heavy components
5. Convert and compress imagessave ~0.026 g/visit (235 kB)Medium impact · quick fix

   2 images exceed 300 kB apiece.

   Serve AVIF (or WebP) with responsive srcset sizes, and re-compress oversized files. AVIF typically halves JPEG weight at the same visual quality.

   • kidneys.png397 kB
   • brain2.png374 kB

   WSG 2.9: Optimize media to reduce resource use
6. 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
7. Optimize web fontssave ~0.0076 g/visit (68 kB)Advisory · quick fix

   5 font files total 191 kB, 1 not in WOFF2.

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

   • GT-America-Standard-Bold.woff253 kB
   • GT-America-Standard-Medium.woff252 kB
   • GT-America-Standard-Regular.woff249 kB
   • CanelaDeck-Regular-Web.woff234 kB
   • core-icons.ttf2.8 kB

   WSG 2.11: Use optimized web typography
8. Upgrade compression beyond gzipsave ~0.0066 g/visit (59 kB)Advisory · quick fix

   396 kB of text ships gzip-compressed; Brotli or Zstandard would cut roughly another 15-20%, and browsers without them fall back to gzip automatically.

   Serve precompressed Brotli for static text assets (highest level, compressed at build time) and enable Brotli or zstd for dynamic responses; keep gzip only as the fallback.

   • cse_element__en.js129 kB
   • fbevents.js110 kB
   • async-ads.js45 kB
   • 11602658884977844 kB
   • analytics.js21 kB

   WSG 4.3: Reduce data transfer with compression
9. Set a page-weight budgetAdvisory · moderate effort

   At 3.31 MB per view this page rates F. 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
10. Remove the entry redirectAdvisory · quick fix

    The address that was scanned goes through 1 redirect before the document is served, ending at https://www.harvard.edu/. Every hop is a full round trip on a connection that has not warmed up yet.

    Point links, sitemaps and canonical tags at the final address, and make the host redirect in one hop rather than chaining http to https to www.

    • https://harvard.edu/redirects to https://www.harvard.edu/

    WSG 4.4: Setup necessary error pages and redirection links

Where the bytes are

• Images2.02 MB · 36 req
• JavaScript955 kB · 21 req
• Fonts191 kB · 5 req
• CSS113 kB · 5 req
• HTML30 kB · 2 req
• Data (XHR)8.9 kB · 3 req
• Other559 B · 1 req
• Data (fetch)0 B · 1 req