The Carbon Calculator behind Webzero.earth
In conjunction with the University of Leicester, we have taken CO2 emission data and created our own Website Carbon Calculator. There is a paid-for website report that gives a lot more details of a website’s carbon footprint and details of its electricity consumption etc.
Below is an outline of the general rationale behind the need for a website carbon calculator and how we have gone about making our own:
Can a website emit CO2?
The World Wide Web needs electricity to run. Electricity production, despite the move towards renewable energy sources, still necessitates the burning of fossil fuels, which equates to CO2. Therefore, taking measures to ensure your website requires as little electricity as possible to load onto a device will help reduce the amount of carbon dioxide being pumped into our atmosphere as well as save users money on their energy bills.
As you will see below, the carbon footprint of a website not only includes the electricity needed to send information ‘down the wire’. To get the most accurate total possible, one must take into account the carbon footprint of the hardware and infrastructure that fall within the boundaries of the global digital network.
How does it work?
To calculate a website’s carbon emissions, there five key pieces of data used:
1.Data transfer over the wire
When a website is loaded, the energy used is roughly proportional to the amount of data transferred. We can calculate the data transferred over the wire when a web page is loaded and multiply that by the energy usage data. We make a downwards adjustment for repeat visitors who may have website assets cached on their devices.
2.Energy intensity of web data
Energy is used at the data centre, telecoms networks and by the end user’s computer or mobile device. As this varies for every website and every visitor, an average figure is used.
After completing a meta-analysis of available studies, an expert study from the https://sustainablewebdesign.org/calculating-digital-emissions/ concluded the following information with regards to the breakdown of the of electricity used:
Consumer device use: end users interacting with a product or service. This accounts for an estimated 52% of the system.
Network use: data transferred across the network. This accounts for an estimated 14% of the system.
Data centre use: energy required to house and serve data. This accounts for an estimated 15% of the system.
Hardware production: embodied energy used in the creation of embedded chips, use of data centres, use of networks, and the use of consumer communication devices. This accounts for an estimated 19% of the system.
3.Energy source used by the data centre
To gauge the energy source, it is assumed that all websites use standard grid electricity for the telecoms network and end user (there is no way to determine otherwise).
For the data centre energy use is verified using the Green Web Foundation (GWF) database to see if the data centre is using green energy. If so, carbon emissions are attributed to that portion of the energy accordingly. The GWF database is not 100% perfect and also includes data centres that purchase standard grid electricity but offset their emissions. For the purposes of this calculator, they are treated all the same.
4.The Carbon intensity of electricity
Based on the international average as reported by the International Energy Agency, it is calculated that the following:
475 grams CO2e per kWh grid electricity
33.4 grams CO2e per kWh renewable energy.
There are reports available that give an “electricity map” which can give more geographically accurate picture of the carbon intensity of that region’s electricity grid.
5.Website Traffic
To accurately present a website’s carbon footprint, it is essential to know how many people visit the site, and how many pages are viewed during an average visit. This is not the same as the 'total size of the website' or the amount of disc space it takes up on a webserver.
Our reports are more accurate than any other because our calculations are taken from the CO2 emissions of the most visited pages of a given website.
For example, if the average number of pages viewed per session is 3, we will find the combined CO2 emissions and page weight (in Mb) of the homepage (the most popular page) and the next 2 most visited pages. A more basic and less accurate way of calculating a website’s CO2 would be to simply multiply the CO2 of the homepage by the average number of pages visited.
Further Reading:
For further reading on the electricity used to power websites and the infrastructure, there are the following reports:
The IPCC’s report on the electricity mix: https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf
The report On Global Electricity Usage of Communication Technology: Trends to 2030 by Anders Andrae and Tomas Edler.
Dividing the total amount of energy used by the total annual data transfer over the web as reported in the Nature article, How to stop data centres gobbling up the world’s electricity. This gives an “energy intensity of web data” figure used, as by the website carbon calculator, as 1.8kWh/GB.
Point of note: There is information using data from 2020 that calculates the “energy intensity” as being 0.81 kWh/Gb. This is calculated from the annual Internet Energy of 1,988 Terawatt hours / Annual traffic of 2,444 Exobytes( (https://sustainablewebdesign.org/calculating-digital-emissions/) The problem in calculating any figure to use in our calculations is one of “system boundaries” - what is to be included in the carbon emissions and what do we leave out? Is it solely the energy needed to push the data down a wire?
If so, the figure comes out at 0.06 kWh/GB for 2015 (based on a 2017 meta-analysis called “Electricity Intensity of Internet Data Transmission: Untangling the Estimates:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/jiec.12630 )
The larger figure of 1.8 kWh/Gb is based on broader systems boundaries, i.e. the total systems impact of websites, including the energy usage.