[noodle]

Because the intent of such a hypothetical law would be to reduce/capture C02, but the end result of it is that it financially incentivizes generating more C02 through some unexpended/unanticipated means.

An unintended consequence might be that yes companies do correctly follow the law and adding carbon to concrete is successful, but also adding carbon to concrete in high enough volumes makes the lifetime of the concrete lesser when exposed to rainwater for long enough, or something like that, resulting in the need to replace the concrete more frequently.

Its the difference between people acting in good faith vs neutral/bad faith with respect to the intent of the law/regulation/etc..

[nvader]

Nitpick: The O in CO2 stands for Oxygen, and is the letter O. It looks like you've used the numeral zero, which looks similar but is not interchangeable.

[eru]

That's why your regulation should just directly tax what you don't like (like CO2 emissions), instead of going via some weird proxy that's prone to being gamed.

[noodle]

The potential to game things exists everywhere. Tax CO2 and people will want to find ways to technically reduce CO2.

For example, what if it becomes cheap enough to just convert all the CO2 to CO and we dump masses of carbon monoxide into the atmosphere instead? Or if its cheaper to convert CO2 to CO3 which imminently degrades back to CO2 in the atmosphere - would we be confident that the tax law would correctly handle this scenario where the emissions are technically a different substance? Etc..

[mgrund]

You just tax on CO2e (CO2 equivalent) for any greenhouse gas emission. Same way emission accounting is already being done.

[eru]

The U.S. Sulphur Dioxide Cap and Trade Programme seems to be working pretty well. Our CO2 taxation programme only has to be as good as that one.

Yes, loopholes need patching up. The law doesn't need to be perfect, just good enough that complying with the law is simpler and cheaper than looking for loopholes.