## Carbon Calculators: What’s The Math?

February 2, 2008

best graphic award – link below (UK)

For each person concerned with reducing their personal carbon emissions, there’s a carbon calculator on the internet. Enter in your driving habits, household heating system, and number of yearly trips to the Bahamas and *poof*, your impact on the environment is handed to your all wrapped up in a nice little number. But how do they come up with that little number? And more importantly, who’s they and why should you trust them to accurately calculate your carbon emissions?

One of the most important aspects of a carbon calculator is transparency. The EPA does a great job with this in their calculator located here. Not only do they have a list of all their assumptions, they even have a spreadsheet version with all the formulas you can download. They have the data, after all, they’re the EPA! They take home heating, transportation, waste disposal, and CFL usage into account. However, they miss out on plane trips and other occasional items.

Details can really make a difference, especially when counting transportation emissions. An Inconvienent Truth’s calculator lets you include the make and model of your car, as well as list the number and length of flights you take. They also provide a list of their assumptions. However, in those assumptions they mention that all the aspects their calculator covers account for only 32% of per capita emissions in the US. Therefore, they provide a ranking system that helps measure your emissions compared to the US average.

Including as many aspects of your lifestyle helps achieve the most complete emissions estimate in relation to that overall per capita number. That means looking for a calculator that includes not only your home and transportation emissions, but your recycling, diet, and hot water usage as well. Sadly, most calculators I found revolve around only the first two. Let me know (or comment!) if you find a good calculator that includes some of these extras!

Know who produces your calculator. Government agencies and nonprofits are usually fine, but I would be wary of sites trying to sell products or services based on your results.

Locality is the last crucial step in finding a carbon calculator that is accurate for you. If you live outside the US, don’t just pick a state and use a US calculator. The calculations usually base emissions on the types of power (coal, hydro, etc) prevalent in each state, and these can vary widely. Use a calculator that is designed for where you live. Here are some decent calculators I found for the UK, Australia, and just about everywhere else.

It’s important to remember that no online calculator will likely be complete enough to discover your true and total emissions. What’s important is realizing the difference you can make through sustainable choices to your lifestyle. Some emissions factors you can change more easily than others, and calculators are great at helping you discover those areas in which you can make the largest difference.