How your sluggish website is affecting your carbon footprint as well as your page speed

Every visit to your site triggers energy use across servers, data centres, networks, and user devices.
If your web pages are heavy, inefficient, or poorly optimised, they consume more energy than necessary, increasing CO₂ emissions per page view, slowing load times, and worsening your website’s environmental impact.

In short, page speed, web performance, and sustainability are inseparable.
A sluggish site doesn’t just cost conversions.
It increases your digital carbon footprint.

Page speed and the environmental impact of your website

Page speed is one of the most underestimated drivers of environmental impact in digital experiences.

Every time a page loads slowly, it:

• Transfers more data than required

• Keeps servers and browsers active for longer

• Increases processing on user devices

• Raises overall energy consumption

All of this contributes to higher carbon emissions of your website.

From a sustainability perspective, speed optimisation is carbon reduction – and the savings can be quantified.
Faster web pages require less energy to render, which means improved energy efficiency and lower CO₂ emissions across your digital operations.

This is why improving page speed isn’t just an SEO or UX decision anymore – it’s a sustainability one.

Understanding the digital carbon footprint of your website

Your website carbon footprint is typically measured in grams of carbon dioxide per page view.

That number is influenced by:

• Page weight and file size

• Data transfer per visit

• JavaScript execution and rendering time

• Third-party scripts and embeds

• Caching and repeat visits

• The carbon intensity of the energy used

A lightweight, well-optimised page can significantly reduce CO₂ per page view compared to a bloated alternative.

Multiply that difference across thousands of visits and the carbon impact of your website becomes very real, very quickly.

Real-world impact – what performance improvements actually mean

It’s easy to talk about sustainability in theory.

It’s harder, and more powerful, to quantify it.

A practical example is Hydrastore Ltd, a site we’ve been optimising for several years. In that time we have significantly improved the performance, increasing its Google PageSpeed score from around 60% to consistently 90% and above.

That hasn’t just been a technical win. It materially reduced the energy required to load each page.

According to WebsiteCarbon.com, the site achieves a carbon rating of A – cleaner than 88% of all web pages globally.

Each page view produces 0.07g of CO₂.

To put that into perspective, the Hydrastore website receives in the region of 250 unique visitors per day – roughly 90,000 visits per year.

Based on Website Carbon’s methodology, at 10,000 monthly page views the site would produce approximately 8.12kg of CO₂ per year, using around 16kWh of energy.

That’s roughly equivalent to:

• Boiling water for 1,100 cups of tea
• Charging an average smartphone 1,370 times
• Driving an electric car around 65 miles
• Or the amount of carbon absorbed by one tree in a year

Now imagine if that same website was still running at a slower, heavier 60% PageSpeed score.

Industry research suggests poorly optimised pages can emit significantly more per visit than high-performing, lightweight ones.

Even a 1g difference per page view, across 90,000 annual visits, would equal 90kg of CO₂ per year.

That’s the difference performance optimisation can make.

And there’s still room for improvement.

This is why page speed improvements are not just UX improvements.

They are measurable carbon reductions.

At scale, across multiple pages, higher traffic volumes, or multiple business websites, the environmental impact becomes significant.

Measure and reduce – how to calculate your website carbon footprint

You can’t reduce what you don’t measure.

Using a website carbon calculator allows you to estimate the carbon emissions associated with your web pages and overall digital presence.

Many teams use free tools such as the website carbon calculator by Wholegrain Digital to:

• Estimate CO₂ emissions per page view

• Compare your site against the wider green web

• Understand your site’s carbon intensity

• Identify high-impact digital content

Running a regular website sustainability audit alongside performance audits makes carbon reduction part of ongoing website optimisation, not a one-off exercise.

Where most websites waste energy without realising

The largest contributor to unnecessary website’s carbon emissions is wasted load.

Many sites still load assets automatically, regardless of whether users ever interact with them:

• Hero videos loading immediately

• Background images hidden in CSS

• Fonts pulled from third parties

• Review widgets loading below the fold

• Hidden forms downloading assets before interaction

A useful way to think about this is “Digital Vampire Scripts”.

These are third-party scripts and widgets that quietly consume energy in the background – draining resources, slowing page speed, and increasing carbon emissions without the user’s knowledge or consent.

From a sustainability standpoint, these scripts don’t just hurt performance – they actively inflate your site’s carbon footprint.

Sustainable web design starts with reducing the load

Hero sections, page weight, and carbon emissions

Large hero videos are a common performance and sustainability issue.

From a sustainable web design perspective, forcing every visitor to load a video increases data transfer and carbon emissions per page view, even when the video isn’t watched.

A more responsible approach:

• Display a lightweight static image immediately

• Load video assets later, or only on interaction

This improves page speed, reduces page weight, and reduces energy consumption instantly.

Reducing file sizes improves speed and sustainability

Oversized images remain one of the easiest ways to inflate your site’s carbon footprint.

Reducing file sizes allows you to:

• Improve page speed

• Lower data transfer

• Reduce energy consumption per visit

• Significantly reduce carbon emissions

This is one of the most effective and accessible practical steps to reduce your website’s carbon footprint.

Mobile-first sustainability – performance beyond speed

Sustainability conversations often overlook mobile – yet most website visits now happen on smartphones.

Mobile devices are far less energy-efficient than desktops when processing heavy JavaScript, animations, and complex layouts.
That means poorly optimised code doesn’t just slow the site – it drains the user’s battery faster.

From a sustainability perspective, mobile-first optimisation is energy efficiency.

Reducing JavaScript execution, deferring non-essential scripts, and simplifying interactions:

• Improves mobile page speed

• Reduces energy draw on user devices

• Extends battery life

• Lowers overall CO₂ emissions per page view

This is a critical but often missed element of sustainable web development.

Intent-based loading – reducing digital carbon through smarter behaviour

Anticipating user intent

One of the core principles of implementing sustainable web development is loading assets in line with user intent.

Instead of loading everything upfront, sustainable websites load resources only when there’s a clear signal they’re needed.

Navigation is a good example:

• Load a simple menu initially

• Load complex mega menus only on hover or tap

This approach reduces:

• Initial page weight

• Browser processing

• Energy consumption per visit

And directly reduces your digital carbon footprint.

Third-party scripts and digital sustainability

Widgets such as reviews, and social embeds, are often loaded automatically, even when they’re far down the page.

Lazy-loading these assets:

• Reduces main-thread work

• Improves web performance

• Lowers CO₂ emissions per page view

From a sustainability lens, loading these types of elements only when they’re in the user’s viewport is one of the most effective steps to reducing the carbon emissions of a website.

Fonts, caching, and quiet carbon reduction

Fonts and unnecessary network requests

Fonts loaded from third parties increase network activity and energy use. Self-hosting fonts and loading only what’s required certainly improves page speed.

Cache and repeat visits

Effective caching reduces the energy required for repeat page views. It is a low-visibility but high-impact part of both page speed optimisation and carbon reduction.

Dark Mode and energy efficiency

For sites with a strong mobile audience, offering a Dark Mode toggle can contribute to energy efficiency.

On OLED screens, used by many modern smartphones, dark pixels consume less power than bright ones.
While this won’t outweigh poor performance decisions, it can:

• Reduce energy usage on mobile devices

• Improve comfort for users

• Support a broader sustainable design strategy

It’s a small touch, but in a sustainable digital future, small efficiencies matter.

Final thoughts on page speed as a sustainability decision

• Every web page has a carbon cost.
• Every unnecessary script increases it.
• Every performance improvement helps reduce it.

Improving page speed isn’t just about rankings or conversions, it’s about reducing the carbon footprint of your website and contributing to a more sustainable digital ecosystem.

By choosing to optimise, reduce the load, and design with intent, businesses can:

• Reduce their digital carbon footprint

• Improve web performance

• Lower energy consumption

• Deliver faster, cleaner digital experiences

When performance improvements can save tens of kilograms of CO₂ per year from a single mid-traffic website, the argument becomes practical, not theoretical.

A sluggish website is a carbon problem.
A fast, efficient one is part of the solution.