Evaluate the CO2 emissions of a website is a quite complex operation. Using those four pieces of information, we arrive to a satisfying estimation:
When a weboage is displayed, the energy used is almost proportional to the amount of data downloaded (images, style files, ads, …). In order to evaluate the energetic consumption of your website, we use an average data quantity of 2 megaoctet per webpage (2 Mo/page). This statistics is constantly updated on httparchive.org.
The energy consumed in the ICT sector can be divided in three groups: the datacenters, the cable networks and the interfaces fixed and mobile used to display the web pages. The figures we took into account here are dated from 2017 and come from this article: On Global Electricity Usage of Communication Technology: Trends to 2030. We then divide this total energy consumed in the ICT sector by the amount of data transmitted on the global internet worldwide found in this article from Nature: How to stop data centers gobbling up the world’s electricity. All this research lead us to an average energy density of the data of 1.8 kWh per gigaoctet (1.8 kWh/Go).
The carbon share in the energy mix is given as an average for all EU countries by the the International Energy Agency. In 2018, this average was equal to 269 gCO2/kWh.
With all the preceding pieces of information, we can assess the CO2 emissions of an average webpage. Multiplying this result by your volume of pageviews, we get the yearly total emissions of your website.