CO2 caused by developing a software feature

How much CO2 does creating a typical software feature cause? It’s a complex question but that doesn’t mean we can’t get some CO2 guide figures. I calculated that the use of the computers alone to create a light feature could cause about 60 kg of CO2, while a more intense, heavy-duty feature could cause 300 kg of CO2.

We must make digital visible. The Cloud is on the ground, yet we live in an increasingly immaterial and invisible digital world. Digital has weight. Digital causes CO2. As managers, designers, developers, we should weigh our decisions to create something or not against the amount of damage and pollution it will cause. It’s a climate crisis and every gram of CO2 we can save we should save.

If you want to understand the CO2 impact of digital, look to the devices. A typical laptop or desktop can cause about 300 kg of CO2 during manufacture, with 1,200 kg of stones, gravel, tailings, and slag being extracted in the process. It takes about 40 liters of water to make a single computer chip, with about 200,000 liters of water required to make an average laptop. There is a growing global water crisis.

Software engineer Chris Wiegman estimates that to develop a light, simple feature for a typical app takes about a week of three developers’ time, about 120 hours. I estimated about 140 hours for design/UX, testing, marketing, and management overheads, bringing it to an overall total of 260 hours. A more complex feature can take six developers two weeks to create. With other human overheads included, I estimated about 1040 hours in total.

To understand the CO2 impact of a digital device, you need to know about the manufacturing CO2 and the energy consumed during use. (Recycling is a whole other area of concern which I’m not focusing on here.)

Laptops and desktops can have roughly similar CO2 impacts during manufacture, though desktop environments often have huge screens, which themselves can cause as much CO2 to manufacture as the computer itself. Desktops are also much more energy intensive to use. Taking the above into account, along with other factors, I’ve estimated that the CO2 impact for using a laptop for an hour is about 107 grams, and for a desktop about 223 grams.

If the development environment used a 50:50 split of laptops and desktops with two screens (one of them 30”), then developing a light feature would cause about 60 kg of CO2. Removing the 30” screen would reduce CO2 to 43 kg. Doing everything on laptops would cause 28 kg of CO2. Doing everything on desktops with two screens would cause 93 kg.

A heavy-duty feature with everyone using desktops and two screens could cause about 370 kg of CO2. If instead, everyone used laptops, that CO2 figure would be 111 kg of CO2, a drop of two-thirds.

Key lesson: the amount and type of hardware you use has a big impact on the amount of CO2 that you cause while going about your work. As a basic principle, the lighter and the smaller the better.

Developing software fuels the climate crisis. If you want to understand software pollution, you must understand the pollution caused by the devices upon which the software is developed and runs.

Podcast: World Wide Waste
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