[mr_toad]

A Pigovian tax, set correctly, will actually remove the deadweight loss caused by a negative externality. However, it is very difficult in practice to measure the negative externalities of something like sea level rise, especially when the effect could be centuries in the future.

[imtringued]

A perfect pigovian tax is rarely necessary. Just 10% of the ideal rate is already sufficient in a lot of cases simply because of the fact that a lot of harmful activites are free and not tracked.

Let's say there is a wood stove that increases cooking efficiency by 2x, this means a lot less trees have to be cut down for cooking. However to a person for whom trees are free, they aren't going to buy a better stove just to save on emissions, they will only start once they run out of trees which is when it is already too late. By charging a fee per tree, even if it is a token amount, people will start calculating and weighing whether cutting down more trees or less trees and buying the stove is the better option. Once they have made the initial investment they may even tell their neighbours about it. A single person changing their mind, can change the minds of everyone.