I disagree that would be fair, and it certainly wouldn't achieve a good result.
If emissions are attributed the country where they are physically made, then it incentivizes rich countries to offshore all their manufacturing to poor countries - which is exactly what's happened here in the case of Britain.
If the choice is between poverty and low emissions, of course developing nations are going to have lax regulations.
There's always an incentive to offshore to where costs are lower. A carbon tax like you suggested at least prevents hiding the costs of CO2 emissions across national borders. This is fair to both consumers and producers but it is not going to be costless to developing nations. Developing nations will either need to match developed ones on energy supply cleanliness or see their export oriented cost competitiveness eroded. This is a good thing for all parties in the long run but it is also a real cost.
If emissions are attributed the country where they are physically made, then it incentivizes rich countries to offshore all their manufacturing to poor countries - which is exactly what's happened here in the case of Britain.
If the choice is between poverty and low emissions, of course developing nations are going to have lax regulations.