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Vegetables and calorie counting top view, intended to show how these values are easier to find than CO2 emisisons

What’s the Difference Between a Calorie and CO2?


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A chalkboard with an image of various vegetables and their calorie values

Just about everything about calories and CO2 are different, except they are both measures of something. A calorie is a unit of of energy, and CO2 is a molecule. On the other hand, there are some similarities: I’ve never seen or touched a calorie, and I haven’t seen or touched a pound of CO2. In a way, both are meaningful to me, only because scientists tell us they are meaningful.

There is one particularly important difference between the two I’d like to explore: Most of us think we know what a calorie means, but almost none of us know what CO2 means.

So, what’s a calorie? Most of us think of calories as pesky reminders we are eating too much food. In the United States restaurant menus now list calories next to each item, and many of us think of 1,500 – 2,000 calories as a ‘normal’ daily intake of calories. On the other side of the equation, the machines at my gym tell me how many calories I burn during my half-hearted half-hour workout.

For humans then, calories are generally consumed in the form of food, and “burned” in the form of work or exercise. Of course, there are much broader implications for calories outside the human metabolism, but most of us can’t remember what they are, really. For me, all of that was tenth grade chemistry, and not much more.

I’m not convinced these calorie numbers are “accurate”, especially on the energy burning side, but in a way it doesn’t matter. In the American mind we now have a context for calories. For me, a HIGH daily caloric intake is 3,000 calories, and a low daily intake is 1,500. A strong day at the gym might mean burning 500 calories, and a weak day might be burning 200 calories. My daily experiences combine with some conception of calories, that make these measures meaningful, even if I still don’t REALLY know what a calorie is.

Let’s contrast the broad conception of calories with the broad conception of CO2. Do you have any conception or rules of thumb for pounds CO2? Here is one I didn’t think of until recently: When you burn a gallon of gas in your car, you generate 20 pounds of CO2 in the air.

I just drove on a long car trip and covered more than 1,000 miles. How many pounds CO2 did I generate? Since my Prius gets about 50 miles per gallon, and I consumed about 30 gallons, my trip cost 600 pounds of CO2. If I flew a direct flight in an airplane the same trip might have cost more, and If I flew over two legs, the same might have cost even more than that. I’m driving back in the car next week, but fortunately, since I will carry a passenger with me, we get to split the CO2 generated: CO2 consumption can definitely include economies of scale.

At some point I need to think about whether I should have taken the trip at all, because the CO2 expense was quite high. On the other hand, I’m making progress because I’m at least building a framework in my mind for the CO2 cost.

We think a solid first step we should all take is to build up mental frameworks for what a pound of CO2 means. Even though you can’t see it or touch it, pounds of CO2 exist, and are generated as a result of our behaviors. We should all try to understand those behaviors, and their relative costs. Once we get these firmly in mind, we can optimize the decisions we make.

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