The European Union rolled out a plan this week to impose “climate tariffs” against countries that lack aggressive emissions-reduction policies, potentially presaging a trade conflict that could complicate the fight against global warming.

Not to be outdone, Senate Democrats as part of a sprawling $3.5 trillion infrastructure and climate spending plan this week pledged to impose a “polluter import fee” on exporters of carbon-intensive goods, though it is far less detailed than the EU’s plan.