You can bypass all of that messy calculating economically speaking. The easiest way to calculate the marginal cost of 1 tonne of CO2 is to create a market and

You can bypass all of that messy calculating economically speaking. The easiest way to calculate the marginal cost of 1 tonne of CO2 is to create a market and find the smallest amount you can pay someone else to reduce their emissions by 1 tonne. These carbon credits exist, and they generally run for ~$40 per tonne. I presume they work, for example, by paying the premium for fully renewable energy versus non-renewal energy, thus converting some amount of electricity generation which would have been CO2 emitting into non-emitting for someone who is paying the non-renewable rate. They could also be indirectly reducing CO2 emissions by helping to pay for CO2 reducing R&D or other such projects. Or I suppose you could pay someone to extract the CO2 directly, but I would guess that's the least efficient way to spend your dollars presently.