If Trump halts or severely curtails international shipping of consumer goods, how much CO2 will not be released by reduced emissions?

Tariffs are protectionist economic policy, and right now consumers will bear the cost. A lot of direct-to-consumer business relies upon free shipping to make the sale, and I really suspect people are going to balk at the shipping prices and duties.

How much global CO2 each year is a result of to-consumer shipping? And how much would a 1-43% reduction be?