My rule of thumb is based on how much money one spends. My reasoning is as follows: it isn't too far off to say our economy is based on fossil fuels. Spending money is taking part in this economy. How much one takes part in that economy tells how much one is responsible for the pollution it creates.

What about people who spend money of organic, fair trade goods, etc.? In the end, that money will be spent by others on goods of the traditional economy.

I'm not too sure about the second part, so criticisms are welcome.

A good first approximation, surely. Money is a good proxy for consumption. Not true for leasing a fancy apartment, though, so you'll want to adjust it.

The idea that money you spend then gets spent by someone else on consumption and that you caused that is a little too hand-wavy for me. But I do suspect that a lot of the politically-correct consumption is not as great as it seems when you look deeper.

Agree in this approximation. In an ideal world, monetary value would be more closely aligned with energy consumption and in turn aligned with productivity, where productivity is less aligned with monetary value and more aligned with the sunk energy cost.

That's only a starting point. Money spent = a kind of 'cost' function, with 'cost' representing raw materials, energy etc used to produce something. Higher cost = more resources used / more damage to environment.

But that's only accurate if all costs (including environmental) are somehow accounted for in market price(s).

That is rarely the case. Apart from the difficulty of assigning $$ values to things like tropical forest cut down, mountain top removed to get copper ore, water used & polluted, or what have you.

Also it doesn't include social costs. If product is cheap but someone's health suffered, or profit helped dictator to reduce press freedom in producing country, is product still cheap?

Too many unknowns & externalities - $$ spent is a poor indicator.

"All models are wrong; some are useful."