China to place outrageously high import taxes on imported cars!

Something which has never made any sense to me is why can China place a huge excise taxes on imported vehicles, while in the mean time we cannot place any kind of tax on their wares. If we were to do so every nation in this world would scream with bloody murder that we were practicing protectionism. I've got an idea why don't we place a carbon tax on them since they are the worlds biggest polluter. I speaking of something along the lines of the cap and trade deal, whereby it would become painful for them to trade with any other nation. I think the only way this could be done is to do it as a group through the UN!