Uploading and downloading the bits and bytes that make up the internet uses a lot of electricity. Breaking the internet down to a systems level, data transfer over networks accounts for an estimated 14% of the web’s total electricity consumption. Networks are also globally distributed, meaning that the bytes you downloaded to render this web page in your browser are probably passed through several different electricity grids. Those grids are made up of different mixes of green and fossil fuel energy.

Being able to measure and account for the emissions of digital services is increasingly important, especially as carbon emissions reporting becomes a mandated part of business operations. Outside of the corporate space, consumers are also increasingly demanding greater visibility of CO2 information for the goods and services they use.

In order to meet the growing demands for reporting and transparency, developers need a way to measure the carbon emissions associated with the apps, sites, and software they build. On the server side, we’re seeing more providers build carbon reporting into their platforms. However, on the application side, it’s largely up to developers themselves to implement solutions. That’s where libraries like CO2.js come in handy, providing a set of research-based, standard calculations that enable developers to quickly add carbon awareness to their products and projects.

What is CO2.js?

CO2.js is a JavaScript library that allows developers to estimate the emissions associated with their apps, websites and software. At its core, CO2.js takes an input of data, in bytes, and returns an estimate of the carbon emissions produced to move that data over the internet. It can be run in Node.js server environments, in the browser, as well as on some serverless and edge compute runtimes.

Why use it?

Being able to estimate the carbon emissions associated with digital activities can be of benefit to both development teams and end users. The carbon emissions of the internet are something that is abstract, and out of sight. Using CO2.js allows these emissions to be surfaced, visualised, and presented in ways that make it easier for people to comprehend and act on.

The possible uses for CO2.js are wide and varied. It can be used in user-facing applications to give visibility to the carbon impact of user activity in the application. Users uploading files, or downloading content, could be notified of the impacts of those tasks. Large, carbon-intensive, data transfers could also be blocked or limited. Users could also have the option to set a carbon budget for their browsing or use of an app, website, or online service.

Behind the scenes, developers could look to use CO2.js as part of their deployment workflow. In the same way that web developers might set a performance budget for their site, a carbon budget could also be used. If a website or app exceeds a threshold for carbon intensity, then an alert can be raised or a new deployment can be blocked. The data from CO2.js can also be used as part of internal monitoring tools and dashboards.

Office managers and sustainability teams could also use CO2.js to track the carbon intensity of data usage within an office environment. Plugging network data usage into CO2.js can allow for monitoring and reporting on the digital usage footprint of an organisation or business.

CO2.js today

CO2.js can do more than just estimate the carbon impact of data transfer on the internet. It also includes functions that use The Green Web Foundation’s greencheck API to determine if a website or domain is hosted on a green web host.

In the wild, the CO2.js package already receives close to 2000 weekly downloads on NPM. It is actively used by website testing tools like Ecograder, and performance tools like SiteSpeed.io to track and display website carbon emissions for users. Website analytics service Cabin also use CO2.js to calculate emissions for page views and historical analysis of CO2 for each page.

CO2.js is covered by an Apache 2.0 license. This allows for the library to be used in digital tools and services. Since the code is kept on GitHub, and is also open for anyone to review, fork, modify, and contribute to. As we’ll touch on a little later, any datasets and figures used in CO2.js are also open, keeping with the themes of open-source, open data, and Open Climate.

Models available for estimating digital carbon

There are a few different models that can be used to measure digital carbon emissions. CO2.js includes two of these – the OneByte model, and the Sustainable Web Design model.

Sustainable Web Design

By default, CO2.js uses the Sustainable Web Design model developed by a collaboration of Wholegrain Digital, Mightybytes, Medina Works, EcoPing, and the Green Web Foundation. It is designed for helping understand the environmental impact of websites, as well as digital products and services.

This model segments the system (the internet) into four parts – data centres, networks, end-user devices, and device production. Based on the bytes passed to it, the Sustainable Web Design model calculates the energy used by each part of the system. These figures are then converted to carbon estimates using the global carbon intensity of electricity from the Ember annual global electricity review.