HOW TO REDUCE YOUR WEBSITE'S CARBON EMISSIONS

Images are the single biggest driver of page weight on most websites. Converting to WebP or AVIF reduces file size by 25–50% compared to JPEG, with no perceptible quality loss. Use tools like Squoosh, ImageMagick, or your CMS's built-in optimization. Serve appropriately sized images using srcset — a 1500px image served to a 375px mobile screen transfers 4× the bytes needed.

Typical saving: Often reduces total page transfer by 30–60%

Modern JavaScript bundles are large. Unused libraries, dead code, and entire frameworks loaded on every page add weight without value. Run a coverage audit in Chrome DevTools to see what percentage of your JS is actually executed. Tree-shake dependencies, code-split by route, and defer non-critical scripts. Aim for under 100KB of initial JS for content pages.

Typical saving: Can reduce JS transfer by 40–70% on typical marketing sites

Each analytics, retargeting, chat, and A/B testing tag loads its own script, often from external servers that add latency. Run a tag audit: list every active script tag, who owns it, and whether it's still used. A quarterly tag audit typically uncovers 2–5 scripts that can be removed immediately. Use a tag manager to load non-essential tags asynchronously or after user interaction.

Typical saving: Removing 3 unused tags can save 200–500KB per page load

Autoplay video is the fastest path to a D sustainability rating. A 15-second background loop can transfer 20–50MB on the first load. Replace autoplay video with a static image and a poster, then load the video only when the user clicks play. If video is essential, use adaptive bitrate streaming (HLS) via a CDN and never autoplay on mobile.

Typical saving: Removing one autoplay video can cut per-load data transfer by 50%+

Don't transfer assets the user hasn't seen yet. Use the native loading='lazy' attribute for images and iframes. For content below a long fold, defer JavaScript components with dynamic import(). The goal: only transfer what's in the initial viewport, load everything else on demand.

Typical saving: Reduces initial transfer by 20–40% on content-heavy pages

A CDN doesn't reduce the amount of data transferred, but it reduces how far data travels — and shorter routes mean lower energy use. A CDN also enables better caching, so repeat visitors load far fewer bytes. Most modern hosting platforms (Vercel, Netlify, Cloudflare) include CDN delivery by default.

Typical saving: Reduces energy-per-byte by shortening network paths; cuts repeat-visit transfer to near-zero for static assets

The same byte transferred over a server powered by solar produces less CO₂ than one powered by coal. The Green Web Foundation maintains a database of verified green web hosts. Migrating to a host with credible renewable energy commitments can cut the carbon intensity of every byte your site transfers.

Typical saving: Can reduce effective CO₂ output by 50–90% depending on current host's energy mix

Custom webfonts load in multiple weights, styles, and formats. A single typeface at four weights can add 400–800KB. Options: switch to the system font stack (no download), subset fonts to only the characters you use, or load a single font weight with font-display: swap to avoid render blocking.

Typical saving: Typically saves 100–600KB depending on number of font files

Long cache-control headers mean returning visitors transfer almost nothing for static assets. Set cache-control: max-age=31536000, immutable on all hashed JS, CSS, and image assets. Configure your CDN to respect these headers. First-time visitors still transfer everything, but most traffic is repeat visitors.

Typical saving: Reduces per-session transfer by 60–90% for returning visitors

None of the above techniques deliver measurable value without measurement. Without tracking, you can't know if an optimization worked, or if a new page section added by marketing last month undid your gains. Set up automated daily carbon scans and watch your A–D rating and CO₂ figure trend over time.

Typical saving: Enables continuous improvement rather than one-off wins