When the permit prices become large enough to have a significant effect on CO2 emissions, there will be political pressure to introduce tariffs on imports that offset the advantage of countries with low permit prices. Such offsetting tariffs would have to differ among products (being higher on more CO2-intensive products) and among countries (being higher for countries with low permit prices).
当执照的价格对二氧化碳的排放量影响力足够大时，国内就会有政治上的呼吁，要求对那些牌照费用较低国家的产品增收进口关税。这些关税也会因产品而异（排放二氧化碳越多的产品征收税额会越高）。这种复杂的税收体制其实就是各国政府的一种贸易保护主义措施，这种贸易保护主义早在50年前的关税贸易总协定中就已经被禁止使用。