Measuring Carbon Footprint: Flawed, but Essential


I recently read Mike Berners-Lee’s excellent book How Bad Are Bananas: The Carbon Footprint of Everythingwhich uses detailed research and painstaking calculations to give realistic ideas of the carbon* footprint of many of the things we do in daily life. What’s the difference between buying asparagus and frozen peas? How does train travel compare to car travel? What’s the impact of a traffic jam? Berners-Lee answers these questions and many others.

One catch is that neither Berners-Lee nor anyone else can give exact numbers for any of these things. For example, the carbon footprint of eating a banana differs a whole lot depending on whether you’re buying it practically off the boat in Miami or from a grocery store in Topeka, Kansas because of the transportation element. The impact of driving a car depends not only on the kind of car, but also on its age, how long you plan to keep it, how well it’s maintained, how often you drive it, and many other factors.

Some of these complications are minor and can be ignored, but others are major. For example, you’d think that between clothing made from natural fibers and clothing made from polyester or other petroleum-based products, the natural fiber clothing would always be greener–but what about laundry? It turns out that washing and drying clothing can be a much bigger factor than the manufacture of the clothing in the first place, and a pair of jeans requires much more energy from a dryer (if you use one) than a pair of synthetic fabric pants.

An even worse complicating factor is that different sources disagree hugely on what the footprint of a particular item or activity really is, and most of these sources greatly underestimate the footprint. For instance, you may have heard statements about the carbon footprint of different vehicles, but in many cases those statements only cover the fuel consumption of the vehicle, and even then don’t take into account the infrastructure and supply chain necessary to deliver the fuel, but rather just what’s coming out of the tailpipe. Berners-Lee makes a special effort to be complete in this regard, but even he readily admits he is likely to be missing some factors in at least some cases.

This doesn’t mean that we have to nail down every last gram of impact and get some kind of complicated analysis of every little thing we do. It also doesn’t mean that because the answers can’t be exact most of the time, we should give up on counting carbon. It just suggests that the most useful approach is to understand carbon footprint numbers as guidelines and to make the best decisions we can based on those guidelines.

For example, it’s next to impossible to quantify exactly what the footprint of manufacturing and transporting a solar array is, or to know the potential footprint of the electricity the array replaces (though it’s often safe to assume it’s from coal, for reasons explained in the book). At the same time, it’s easy to see from even rough calculations that regardless of where these numbers land exactly, installing an effective solar array makes for a huge reduction in carbon footprint.

Annoyingly (to me, anyway), Berners-Lee is not much of a booster of solar power for reasons essentially unrelated to its carbon impact, and I think his analysis on that point is off-target. This is one of my many minor peeves about the book, yet on the whole it’s extremely useful. I hope to cover more of both its good and bad points in future posts. In the mean time, if you’re at all interested in understanding your personal impact on the climate–and everybody else’s, for that matter–may I suggest you buy the book?

*Like Berners-Lee and many other people who discuss the subject, I use the term “carbon footprint” as shorthand for “carbon dioxide equivalent,” which is to say the impact of all greenhouse gases, all of which can be calculated as being equivalent to a certain amount of carbon dioxide (CO2) in the atmosphere. While there are a variety of greenhouse gases, CO2 is the most abundant, though it’s not as damaging gram for gram as most of the others. Anyway, it’s unnecessarily complicated in most situations to talk about “carbon dioxide footprint, nitrous oxide footprint, methane footprint, and refrigerant footprint” and then to have to do a bunch of extra math from there when we can just use conversion factors and talk about “carbon dioxide equivalent.”

Photo by liknes

One thought on “Measuring Carbon Footprint: Flawed, but Essential

  1. Pingback: “Kic”: A Universal Unit for Climate Impact | Face Climate Change

Comments are closed.