> Is that unreasonable? Carbon dioxide is an externality, and it needs to be accounted for accordingly.

Yes it is unreasonable. Spending money to reduce carbon is just a subsidy for other countries who DGAF and will emit both theirs and yours.

When your country emits more CO2 there’s more CO2 in the atmosphere independent of what anyone else does.

So it’s true each individual country only receives a fraction of the negative impact of their own emissions, but that fraction isn’t zero and therefore should be taxed to maximize economic efficiency. Further joining international treaties to agree to collectively tax carbon at a higher rate representing the harm across all those countries is even more economically efficient.

Do you apply this logic for everything?

Dumping your waste, others be damned, is a hell of a way to live.