Teaching a course on sustainability at NUS Business School, adjunct professor Andreas Birnik wanted his students to measure their own individual environmental impact resulting from their lifestyles and purchase choices.

The apparently obvious solution was to turn to the growing number of online carbon calculators, an increasingly popular tool for environmentally-aware consumers looking to gauge and mitigate their contribution to emissions of so-called greenhouse gases.

But for Birnik there was one overriding question – how reliable are they?

“I found it troubling that results could vary by a wide margin between different calculators,” he says. “I wanted to get my students to compute their own carbon footprints, but I did not know which calculator to trust.”

ThinkAloud4Birnik likens the disparities between some of the most popular carbon calculators to the situation of a health-conscious consumer looking for online help to assess their own body mass index. If the situation with carbon calculators were reflected in this case, the same individual might be told they are underweight, normal, overweight, chronically obese, or anywhere in between, entirely depending on the calculator they use.

With reliable results, online carbon calculators would seem to be an ideal way to support the growing number of consumers looking to mitigate their environment impact through their purchase decisions.

But with different calculators giving widely varying outputs, Birnik says the cumulative result is only increased consumer confusion and ultimately little impact on the primary goal: securing the future health of the planet.


Researching deeper into the problem, he set out to evaluate and rank some of the most popular carbon calculators according a series of a standardised benchmarks.

Those which focused specifically on buildings, food or transportation were eliminated as they were not considered comprehensive. To round out his list, he added three more calculators offered by well-known providers of carbon offsets to consumer buyers.

With a representative list of 15 apparently comprehensive carbon calculators, Birnik then reviewed available climate literature to compile a standard of 13 key principles against which to measure them. These ranged from measuring an individual’s consumption patterns of food and transportation, to energy consumed in their country of residence.

Calculators which complied with a principle received a ‘Yes’, with the total number of ‘Yes’ marks signifying the final score. A subjective rating of “Strong” was given for scores above 7, “Average” for scores of 5 and 6, and “Weak” for any scores below 5.

The most critical benchmark of a calculator’s credibility, Birnik says, is that the sum of individual emissions within a country equals the country’s emissions as a whole.

While that might seem obvious, only three of the 15 calculators came anywhere close to delivering such a result; seven others fell into the “average” category and the remaining five were classified as “weak”.

Credibility gap

For Birnik, the results clearly showed a significant gap between commonly available calculators and the findings from scholarly articles focused on carbon footprinting.

carbonstory280Birnik’s research gave birth to the CarbonStory projectA central problem, he says, is that documentation behind even the most popular calculators is generally poor and as a result, users do not know which greenhouse gases were included in their calculations and which sources were used.

Additionally, Birnik says, none of the sample calculators appear to base their estimations on consumption-based data and neither do they adequately adjust their results according to household income.

Disappointed with the varying results, Birnik’s research inspired a new project – working with two former colleagues he created the website CarbonStory (www.carbonstory.org).

Developed as a social enterprise, the site allows users to become a part of the solution to climate change by sponsoring carbon offset projects around the world.

CarbonStory allows users to calculate their personal carbon footprint using a calculator crafted from Birnik’s research findings. However, the most important feature, he says, is the site’s ability to connect the projects with the hearts and minds of consumers through the use of images, videos and stories.

Making an impact

“CarbonStory was born to enable people to make a real life impact towards fighting climate change,” he says. “They do not have to change their lifestyles before they are allowed to take part.”

One of the ways the site aims to be different from others is by providing details about projects which users support.

Rather than buying carbon offsets from anonymous projects, Birnik says, users know exactly what projects they are supporting. They get a personal page visible on the web and can make Facebook posts whenever they support a project.

Another advantage is that CarbonStory’s calculator uses data from 147 countries while most online carbon footprint calculators only provide estimates for users within a single country.

Unique packages such as CarbonStory, with its standardised principles, may be the way to go in helping to ease guilty consciences when it comes to climate change.

As Professor Birnik says, “this doesn’t mean that we think that people should avoid reducing their carbon footprint and simply sponsor projects.”

The key, he says, is to make it as easy as possible for people to get started.