Hopefully the border tariff includes the CO2 cost of shipping. If the tariff is high enough then this might actually encourage local production, instead of shipping partially finished products 10 times around the world.
In other words, it's not marginal numbers that matter, it's absolute numbers, and something absolutely has to be done about those numbers.
--
[0]: https://www.weforum.org/agenda/2020/10/shipping-industry-car...
In a world that has climate change under control, there's for sure going to be a reduction in pollution produced by global shipping, but in the world we live in there's much better places to start than by limiting global shipping.
That said a carbon tax certainly does limit shipping, as some of it will no longer be profitable. Fortunately when doing it with a carbon tax, it just so happens to be the shipping that we shouldn't have been doing in the first place!