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User Perceptions of CO2 Calculators: A Brief Review

COMPAIR is developing a carbon footprint calculator and simulator to increase environmental awareness among citizens and to help them make more sustainable lifestyle choices. To ensure that our tool is what people like and want to use to change their daily habits - in other words, that they see it as a vehicle for behavioural change - we looked at some past studies that assessed CO2 calculators from an end-user perspective. The main findings were distilled into recommendations for the technical team working on improvements to the tool. The recommendations might also be of interest to other projects developing their own household emissions calculator.

Household carbon emissions calculator

CO2 calculator output

In this brief review, the focus has been not on the technical implementation[1] but on the perceived usefulness of CO2 calculators, as we think this kind of feedback is more relevant at this stage to make our tool stand out in a crowded landscape (there are several dozen emissions calculators currently available). The main questions driving our research are: what did past evaluation studies find? Are CO2 calculators easy to use? Do people use them often? Crucially, do they use results to inform lifestyle choices?

In 2018, the 'Your Carbon Footprint Identity' survey results were published, providing insight into user experience and preferences with CO2 calculators.[2] The sample included 216 responses from the general public. The survey assessed participants’ knowledge of greenhouse gas emissions and whether carbon calculators were effective in changing participants’ behaviour.

Out of all survey participants, a majority (53%) had used a CO2 calculator in the past. However, less than 10% could remember their calculated footprint measure. Slightly more people (16%) said that a carbon footprint calculator helped them change their daily energy consumption habits.

A 2020 study with a bigger sample (n=4245) assessed the use of the carbon calculator by the Global Footprint Network.[3] While the majority thought the tool was easy to use (93%), only 23% of respondents indicated the calculator provided them with the necessary information to make behavioural changes and reduce their personal footprint.[4]

Although some calculators are reportedly easy to use,[5] others ask questions that, for most of us, would be hard to answer accurately without preparation. Unless users have had some kind of monitoring system in place to track their habits, answering lifestyle questions quickly and precisely can be challenging. How many people know, off the top of their head, what distance they travel by car in a year, how many flights they have taken that are domestic, short- medium- and long-haul, how many times they travel by train and over what distances, what their fuel and electricity consumption has been, how much waste they generate, how much stuff they recycle? Most of us won’t have ready answers to these questions, and quite a few will probably struggle trying to figure out where to look for the information. Is it utility bills? Travel tickets? Google maps?

Even if people find the right information, an even bigger challenge is to convert acquired knowledge from the calculator into actual life changes. Past studies concluded that just presenting numbers from CO2 calculators is not an effective way of trying to influence user’s lifestyles.[6] Another challenge is retention. Footprint calculators are typically used by environmentally conscious individuals, and even in this group it is hard to get people to use the tool more than once.

To improve retention and ensure that a CO2 calculator is more than a statistics sharing tool, literature recommends integrating behavioural intervention strategies in the form of pledges, goal setting, and gamification-based challenges oriented towards groups or individuals. One strategy highlighted as being particularly effective involves placing calculators in an educational setting. According to the authors,[7] embedding footprint calculators in a curriculum[1]  can enhance sustainability teaching and offer students scientific, transdisciplinary insights that can, at a minimum, increase environmental awareness and potentially inspire them to lead more sustainable lifestyles.


All these findings and insights allow us to formulate recommendations for our technical team and others working on a similar tool.

  • Raison d'etre: Agree on the main objective of the tool: should it be statistics-sharing? Inspiration? Lifestyle change? If it's the latter, introducing elements of environmental psychology will be necessary to motivate users to change habits. Information provision offers a potential pathway to change, however on its own it is hardly an effective strategy. Hence the need for pledges, gamification, and goal setting techniques.

  • Educating users: As well as asking detailed questions about consumption, the CO2 Calculator would need to explain basic energy concepts, as well as how daily activities, energy use and emissions are related. Past studies show that many people don’t know what 1 kg of CO2 emissions or 1 kWh means in terms of daily activities.

  • Balance simplicity and complexity to make the tool credible yet easy to use. Ask too many difficult questions and people will lose interest before completing the form. However, we also need users to have confidence in the output, and this can’t be achieved by asking trivial questions. The challenge is therefore how to reach both credibility and usability without compromising one or the other. And if we choose to offer the CO2 Calculator to schools (see next point), do we create a simple version for students and a more advanced one for everyone else?

  • Schools: Offer the tool to students participating in citizen science campaigns. According to the literature, education institutions provide a favourable setting for the uptake of CO2 calculators. So far, sensors and PMD have been the focal point of our engagement with schools. By adding the CO2 Calculator to the mix, we increase its chances of post-project exploitation while also delivering benefits to schools (enriched curriculum) and students (better environmental awareness with a potential to change lifestyles).


[1] Many papers talk about the design and characteristics of CO2 calculators, including John Mulrow, Katherine Machaj, Joshua Deanes, and Sybil Derrible. 2019. The state of carbon footprint calculators: An evaluation of calculator design and user interaction features. Sustainable Production and Consumption 18 (April 2019), 33–40.

[2] Mulrow, J., Machaj, K., Deanes, J., & Derrible, S. (2019). The state of carbon footprint calculators: An evaluation of calculator design and user interaction features. Sustainable Production and Consumption.

[4] Andrea Collins, Alessandro Galli, Tara Hipwood, and Adeline Murthy. 2020. Living within a One Planet reality: the contribution of personal Footprint calculators. Environmental Research Letters 15, 2 (Feb. 2020), 025008.

[6] Aksel Biørn-Hansen, Cecilia Katzeff, and Elina Eriksson. 2022. Exploring the Use of a Carbon Footprint Calculator Challenging Everyday Habits. In Nordic Human-Computer Interaction Conference (NordiCHI '22), October 8–12, 2022, Aarhus, Denmark. ACM, New York, NY, USA 10 Pages.

[7] Aksel et al. (2022)



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