How much does a tonne of carbon dioxide weigh?
Um, a tonne? But how do you visualize that?
Alex Bantock of Preoptima recently asked, “How much is 1 tonne of carbon dioxide?” which, like my title, is kind of obvious: a tonne. The problem is, how do you describe something so literally nebulous as a cloud of CO2? How do you get people to understand how big and heavy it is?
Preoptima tried it with volume, a big cube of gas, but also with weight, comparing it to grand pianos and walruses. Preoptima is also preoccupied with buildings, which are made of relatively discrete components like bricks.
Many have tried this over the years; a company named Real World Visuals turned it into an industry, displaying carbon as bubbles containing one tonne of CO2, explaining that “At standard pressure and 59 °F a metric ton of carbon dioxide gas would fill a sphere 33 feet across (density of CO₂ = 1.87 kg/m³).” Here, they have almost buried the Empire State Building in a day’s worth of carbon emissions.
The CAKE electric motorcycle company went to great lengths to construct a box showing the CO2 emissions from making one of their bikes, but I still think this is a problematic visualization.
I have been wrestling with this problem in my upcoming book, The Story of Upfront Carbon, where I wanted some graphic form that everyone could understand, a unit that everyone could relate to.
I was not thrilled with bubbles or boxes; people don’t intuitively get that gas actually has weight. It wasn’t even discovered until 1647 when Torricelli invented the barometer. It also varies with temperature and pressure; the bubbles at the top of the Empire State Building would be larger than the ones at the bottom.
Others have tried the old Olympic swimming pool or the distance a car drives. Will Arnold of the Institution of Structural Engineers has tried to educate the construction industry about embodied carbon by relating it to things we have done in our daily lives; in an article written when he was at ARUP, he noted that your flight to Europe is a tonne of carbon! A year's worth of meat is 2 tonnes! Driving your car is 3 tonnes per year! He gets the scale of it all and compares it to the upfront carbon emissions in buildings to show the impact of design changes.
“What can you do about it? Well as an example, if you agree to columns that are closer together, limit the number of storeys, and allow the engineer to spend more time optimising the structure, you might halve it. That’s a saving of 3000 tonnes of embodied carbon… twenty lifetimes of veganism!”
I thought Arnold was on to something here- make it relatable. But instead of a lifetime of veganism, what about hamburgers? Each one has a carbon footprint of about 12 kilograms of CO2, so a tonne of CO2 is equivalent to 83 hamburgers. But there are also a dozen different calculations of hamburger footprints; they are complicated. And while they are relatable, that isn’t about how much they weigh. It’s not intuitive. Like Arnold’s examples of flying or going vegetarian, you can’t feel it.
In T.S. Elliot’s poem “The Love Song of J. Alfred Prufrock” our protagonist says "I have measured out my life with coffee spoons." I thought this might be a good unit to use; I would call it a Prufrock. But I weighed a coffee spoon, and it was only 26 grams; that’s a bit light. My iPhone would have upfront carbon emissions of 3076 Prufrocks, which is a lot of silverware and is not particularly relatable.
In the end, I concluded that it had to be something that would create an image in the reader’s mind, and I picked the ACME anvil that kept squishing Wile E. Coyote. I assumed it to weigh 100 kilograms and explained that my MacBook Air computer has upfront carbon emissions weighing 2 official ACME anvils.
My little 188-gram phone’s footprint is a bit less than one anvil but 425 times as heavy as the phone. Imagine walking around carrying most of the weight of an anvil in your pocket.
A Tesla Model 3 is about 140 anvils. I know that not many people have tried to lift an anvil, just as not many have tried to pick up Preoptima’s grand piano or walrus, but they know that it is heavy, and I thought it was an unforgettable image.
There are so many ways to visualize CO2; a tonne of it could be a 33-foot bubble, 38,411 Prufrocks, 8200 kilometres of driving, one flight to Europe, 83 hamburgers, 166 trees absorbing CO2 per year, 2 grand pianos, or 10 standard ACME anvils. However you measure it, it is far heavier and bigger than most people imagine.
I hope Lloyd checks and double-checks his carbon emissions figures for his book.
Figuring in high-atmosphere climate forcings, a flight from NY to London is about 1.5 tons equivalent. And, where's the evidence that the average footprint of animal products in one's diet is 2 tons? Finally, because of the range of farming techniques and different landscapes, putting a solid figure on the footprint of, say, a pound of beef will be a challenge--and, not even considering that some operations can use livestock to sequester carbon in soil. I think Lloyd may tend to downplay flight emissions and overestimate animal-product consumption, perhaps a hidden bias of his.
I was trying to visualise tonnes of animal manure for an upcoming article. I was really struggling with the large numbers (hundreds of thousands of tonnes) so I needed something that was familiar and weighed many tonnes. In the end, I used concrete mixers.