I've been measuring my carbon footprint out of curiosity. If I were still a teacher of environmental science, I'd be having students to do this as part of their studies – and then exploring the implications and limitations of what was revealed.
To cut to the chase, my footprint [ c/o carbonindependent.org ] was almost 9 tonnes which is twice the world average, about 60% of the UK average, and about 6 times what the website says is "sustainable", although it has the grace to put a question mark alongside that piece of speculation.
More than a third of the tonnage is due to the 14 hours flying (mostly to Germany) I ration myself to annually and the next biggest item is heating the house and water, and cooking food. It's the fossil fuel source of all this that causes the difficulty. My electric car and Semington A mitigate some of this, although it's not straightforward to insert these factors into the calculation. Nor is it possible to factor positive factors such as composting or a bee-friendly garden into the calculus. The devil is always in the detail of all this which is why carbonindependent.org is a useful site as there is a lot of background data provided – and it doesn't assume you're a profligate American.
I do not, I should say, live a hair shirt life, and nor do I intend to. But I do wonder [i] what I might do now to reduce the 9 tonnes whilst [ii] keeping the trades-off bearable.