A lot of the discussion around what we need to do to slow down climate change is described to us in tonnes of CO₂. The trouble is of course that most of us don’t know what a tonne of CO₂ looks like. I thought I would try to bring this discussion into terms that most of us would understand by rephrasing it in terms of gas tanks. Keeping in mind that not all carbon emissions come from burning gasoline in a car, a gas tank is still probably a more useful visualization for most of us than a tonne of CO₂. Note also that what we really care about is the total warming potential of all greenhouse gases released into the atmosphere, which is usually measured in CO₂ equivalents. But since the basic unit of measure is still a tonne of CO₂, the discussion below is framed in terms of CO₂.

First of course we have to decide how big a tank we’re going to use. Because there’s a precedent for using a 50 L tank, that’s what I’m going to use as my standard tank. That’s the size of tank you have in a typical smaller car. At 2.3 kg of CO₂ per liter of gasoline, a 50 L tank will produce 115 kg of CO₂ when burned in your automobile engine. Conversely, a tonne of CO₂ would be equivalent to about 8.7 tanks.

To meet its Paris accord commitments, Canada needs to cut its emissions by about 205 million tonnes of CO₂ between now and 2030. (Some of you will say, “but our Paris commitments aren’t enough!” You’re right, of course, but it’s a baseline to aspire to in the short run.) As I write this, the population of Canada is about 37.6 million, so that’s 5.5 tonnes per Canadian per year. That’s about 48 gas tanks per person per year. Note that this figure includes CO₂ emissions from industry and from private use, but keep in mind too that this does not include all of the carbon emissions you are responsible for through your purchases of foreign-made goods, which are accounted for in the country where these emissions are produced. So, for example, if you buy a pair of shoes made in Vietnam, those are Vietnam’s emissions, even though you are the person driving these emissions. StatsCan tried to estimate household contributions to greenhouse gas emissions (not including foreign emissions for goods imported into and consumed in Canada) a bit over a decade ago, and found that households were responsible for about 46% of Canada’s greenhouse gas emissions, either directly or indirectly. Assuming a similar ratio still holds, each of us is on the hook for about 22 gas tanks per year.

I don’t know about you, but I don’t think I fill up my gas tank 22 times per year. Remember: those are 50 L tankfuls. A lot of the times I “fill” my tank, I’m only buying 30 or 40 L of fuel. So I could stop driving completely, and that wouldn’t do it, especially when you consider that I live in a three-person household with just one car, so I can’t count on my wife and son to cut 22 fill-ups of cars they don’t have! The idea here isn’t to think in terms of literal gas tanks, but in terms of gas-tank equivalents. Between the three of us, my wife, son and myself need to cut about 66 gas-tank equivalents out of the emissions we’re responsible for.

There are plenty of web sites that will tell you what you can do to reduce your personal carbon emissions. Clearly, if I can drive less and use my bike or public transit more, that helps. Equally clearly, that alone won’t get us there. One of the things that will make a big difference that politicians don’t like to talk about is that we’re probably all going to have to just buy less stuff. I’m going to pull a few figures from Mike Berners-Lee’s excellent book How Bad Are Bananas? to make this point.

Let’s say that building the car you want to buy will produce 15 tonnes of CO₂, about what it takes to build a midsize car. That’s 130 gas tanks. You could of course avoid causing those emissions by buying a used car, which won’t cause any extra emissions. But of course, eventually someone has to buy a new car (assuming we don’t all start riding public transit, but that only works for urban dwellers), and let’s suppose that you decide that you really want a new car. You could just buy a smaller car. Some cars have an emissions impact of as little as 6 tonnes of CO₂, or 52 gas tanks. Even if you don’t go to the smallest car available, you could easily shave 30 or 40 gas tanks from your emissions just by buying a smaller car.

But wait! Those emissions should be amortized over the time you own the car, right? The average Canadian owns a new car for about 6 years before trading it in. So the impact of your 130-tank car over your period of ownership is about 22 gas tanks per year. Coincidentally, this is how much you need to cut out of your annual emissions, so if you can go car-free, you’ve pretty much done your part (but you might have to find other reductions if a family is sharing a car, as in our case). Going to a smaller car might save 7 gas tanks per year, which is about a third of the 22 tanks per year you need to cut out of your lifestyle. Not bad! But what if you really want that 130-tank car? If you keep it an extra two years, the impact of your new car becomes about 16 tanks per year, so you are reducing your carbon emissions by about the same amount as you would by buying a smaller car, just by keeping your car a bit longer. And obviously, this emissions reduction strategy just gets better the longer you keep the car.

And what about those Vietnamese shoes I mentioned earlier? Making the average pair of shoes and transporting it to a store near you results emissions of about 11.5 kg of CO₂, or about a tenth of a tank of gas. I probably buy two to three pairs of shoes per year, so for me, this isn’t worth thinking about. But if you’re a shopaholic who loves shoes, well, I’ll let you do your own calculation…

I suspect that if you’re going to buy clothes, shoes and accessories and are actually going to wear them until they’re ready for disposal, there probably aren’t significant emissions savings to be made by changing your shopping habits. However, some of us, and you know who you are, do buy stuff we won’t wear much before putting it into the basement. Then those fractions of a gas tank really start to add up. As a general rule, buy less, and buy used if you want to cut your carbon footprint. This applies not only to clothes, but to anything else we buy on a whim and then barely use.

And the general idea of buying what you need and using it applies to food, too. Food waste is a massive contributor to greenhouse gas emissions: Because food is wasted, it is necessary to overproduce food, which leads to deforestation, i.e. loss of an important carbon sink. Moreover, agriculture has a direct energy cost, so more food grown means more emissions from the agriculture sector. Then there is the transport of food that will never be eaten. And rotting food often produces methane, an even more potent greenhouse gas than carbon dioxide. A rough estimate is that household food waste (as opposed to food that is wasted somewhere in the supply chain) amounts to about a quarter tonne of CO₂ per person per year in Canada, or 2.2 gas tanks. Not a huge number, but still about 10% of the emissions you need to cut per year. Roughly speaking, to reduce the amount of food you waste, you have to buy things you plan to eat, and make sure you actually do use it before it goes bad. Sounds simple, but it does take a bit of a mental adjustment to our shopping and cooking habits.

So there you have it. Climate footprint and emissions reductions conceptualized in gas-tank equivalents. Hopefully this helps you understand the size of the problem a bit better, and also puts in perspective some of the things you can do to reduce your climate impact. A lot of the advice comes down to buying less stuff and using it for longer (or using it at all in the case of food). And as an added bonus, if you spend less, you’ll have more money in your bank account for a rainy day. Win-win.