1. Have a single CO2 budget for the whole country, with an aggressive, Hard to change roadmap of yearly reduction of said budget down to zero in the not too long future.
2. Estimate the CO2 footprint of every single product, incl. imports by one or several neutral organizations. This doesn’t have to be perfect as long as it attempts to be fair.
3. Tax every product according to this budget using supply/demand markets (certificates trading).
4. Redistribute the tax, especially to mitigate the hardship on low income households and domestic companies.
In my mind, this would create a gigantic incentive for CO2 reduction for your citizens as well as domestic AND foreign companies. Crucially, it would not require any global agreement and consensus. Apart from perhaps renegotiation or canceling of trade agreements on the side of the country that implements the policy.
Note, that you can replace CO2 by greenhouse gases or environmental impact in general. I just use it as a shorthandle.
Very curious about your opinions.