If they wanted to impose it on China's oil trade with Saudi or Russia, it would have to be done militarily.
And that still leaves the question how to impose a carbon tax on China's domestic coal and oil.
The purpose of carbon tarrifs is to make foreign dirty-energy-intensive products less competitive, compared to less dirty-energy-intensive ones.
Because we already have a way of making domestic dirty-energy-intensive products less competitive. It works great. It's called a domestic carbon tax.
They remove the immediate complaint of "If we impose a local carbon tax on energy, foreign imports will outcompete us, because they don't have to pay it."
A carbon tax is not 'stopping trade'. It's an increase to the price of goods that are energy-intensive to manufacture, or ship.
