Deep-dive into measuring website carbon footprints

At Supercool we care about the environment, and the impact the websites we create have on our planet. That’s why we’re working on a Cultural Website Sustainability Benchmark study and report – to help organisations understand what ‘good’ looks like in terms of the environmental impact of their websites.

In collaboration with our friends atDigital Carbon Online we’re currently tracking the carbon footprints of 67 websites in the UK arts, cultural and heritage sector.

We’ll soon be ready to analyse this data, and will use it to compile a comprehensive benchmarking report. The report will also highlight any common patterns, and suggest opportunities for improvement.

Due to be published in summer 2025, the Cultural Website Sustainability Benchmark Report will be made freely available. So that everyone can benefit from the findings, and everyone can get a better understanding of how to reduce the impact of their own websites.

To collect the data needed for the benchmark report we needed to automatically determine the carbon footprint associated with millions of individual page views, across 67 different websites. And we needed something that would do this not just once, but on a continuous basis. That's where Digital Carbon Online comes in!

Here’s Scott Stonham, CEO of Digital Carbon Online, on their unique – and uniquely thorough – approach to measuring website carbon footprints:

The basics of how it works

Digital Carbon Online automatically calculates the cumulative carbon footprint of entire websites over time, while also providing page-by-page insights into which pages cause the most / least carbon – and why.

Digital Carbon Online assesses the carbon footprint of each individual page (“page weight”) that is viewed by website visitors. These page weights are stored along with the frequency of the visits to each page.

This allows us to determine the cumulative footprint of each page over time, and therefore the cumulative footprint of the entire viewed website.

Find out more about how Digital Carbon Online works

Why does a website have a carbon footprint?

Fundamentally, carbon footprinting looks to determine the greenhouse gas emissions associated with the production of the energy required to deliver a task, service or product.

When it comes to our digital carbon footprint, energy is spent (and emissions created) in many ways. As with any other ‘thing’, our digital footprint comprises the carbon dioxide equivalent (“CO2e”) emissions incurred during the manufacturing process (“embodied emissions”) as well as in the use of the “thing” (“operational emissions”).

For digital “things”, the embodied emissions relate to the process of mining, mineral extraction, processing, refining, assembly, build, test, shipping, logistics and more. It means that digital things – laptops, routers, smartphones, servers, cables, etc – all have a footprint before they are even installed or used.

Operational emissions come from the energy required to run the things, and this is what we primarily focus on for websites.

To determine this, the general practice is to use a proxy for energy consumption, bytes of data. The Green Web Foundation has derived the carbon cost of a single byte of data from the global total energy consumption (and how much of that is from dirty vs renewable energy sources) and the total amount of data transferred.

Using this and the foundation’s published models we are able to approximate the carbon emissions associated with websites as they are viewed by users.

A unique dual methodology approach

There is no such thing as a definitive data point in any field of sustainability - let alone the nascent field of digital sustainability. Every data point comes with a margin of error or uncertainty.

As such, Digital Carbon Online has been built to use two similar, but different methodologies providing a carbon footprint range, instead of a potentially misleading single figure.

Both methods follow the best practices as defined by the Green Web Foundation. They vary in how they determine the byte size of the pages, and as such provide different CO2e values for each page. Our Standard model follows the same byte-counting approach as some other single page website carbon calculators. Whereas our Alternate model takes a different, potentially more realistic approach to assessing the amount of data transferred.

The result is that each page and each website has an associated range of carbon emissions, which can lead to valuable insights into carbon reduction options.

Time-shifting

When building Digital Carbon Online it was important to make sure we’re part of the solution and not just creating more of a problem. As such, we made several important design decisions which needed to be taken into consideration when designing our benchmarking activity.

One of the most fundamental decisions was that the platform was not going to operate in real-time. This meant we could be more intelligent with our data processing tasks, preferring times when the UK’s energy grid was at its greenest.

While our systems run on hosts that use renewable energy, the reality is that there are times when even green hosts consume brown energy. Plus, when we’re dealing with third party websites, plugins, external libraries, content delivery networks, and not to mention all the networking in between, we simply can’t assume that the energy used will be renewable.

As such, we delay our testing and processing to times when the UK’s energy grid carbon intensity is either ‘very low’ or ‘low’. The caveat here is that, since we operate under UK weather conditions, there are times throughout the year where those two levels are very rare. In those situations we step up a level after a certain time period to ensure all relevant data are processed on a monthly basis.

This delayed processing characteristic preferred the longer duration test window (three months) allocated to the benchmarking activity.

Reduced scope

Typically, Digital Carbon Online will monitor all publicly accessible pages on a website. However, to minimise the impact of this research project we decided to limit the scope to the highest frequency pages on each of the target websites.

Under Supercool’s guidance we select the top most visited pages of each website, with an emphasis on trying to ensure we were benchmarking like-for-like – e.g. comparing event listings and booking pages on one site with collection listing and ticketing, on another.

Even still, at the time of writing we’ve already assessed the carbon emissions of more than 8 million page views within the benchmark.

Deriving insights

Regular Digital Carbon Online users get access to their data through dedicated dashboards. Users even have the option to publish their data using a public dashboard transparently. However, this wasn’t a regular study.

As it stands right now – and things could change between now and the final report – we've seen huge variability between individual page weights even using the same methodology. The heaviest page is currently weighing in at 23.5g CO2e per page view, with the leanest boasting a nimble 0.09g CO2e per page view.

Once the data collection is complete we will embark on an activity with Supercool to derive insights and findings, that we’re looking forward to sharing with Arts Marketers at the AMA Conference in Edinburgh this July. 

Hope to see you there!

Digital sustainability resources:

• Sign-up to Digital Carbon Online’s FREE email masterclass
• Supercool + Sustainability – resource hub of FREE articles, tools, webinars and more.