However, I should note that other quizzes have given me 1-4 Earths. A similar range of results is achieved by carbon calculators, as reported here.

The problem is that each has different assumptions behind it. For example, your linked one asked how often I ate beef, a few times a week, a few times a month, daily or what. But it didn’t ask the quantity. So that someone who eats meat as a flavouring, 50 grams a day, ends up with a larger ecological footprint than someone who eats a big 350g steak three times a week.

But they want to make it quick and snappy, most people don’t know how much money they spend on groceries, let alone the weight of beef they eat each time, so the survey just makes some assumptions, something like “each time they eat meat, it’ll be a 220g serve.”

Each survey has different assumptions, and thus each gives different results.

Despite these things giving us numbers, it’s best to think of them in qualitative terms, rather than quantitative. The thing gives you a score, and you compare your score today with your score yesterday. So if I can change things to lower the Earths it takes to support my lifestyle, it doesn’t really matter than Calculator A says I went from 6.3 to 4.2 and Calculator B says I went from 2.1 to 1.5; the point is that I lowered it.

It’s like when you get marks at school, getting an A in January and then a D in February gives you a very different reaction compared to going from D to A! Your parents are concerned less with your absolute grade, and more that you’re getting better – or at least not worse. If you think of these carbon calculators in those terms, they’re more useful. If you get hung up on the exact numbers you get nowhere.