The European Union is scheduled this week to release its plan for a carbon border adjustment—basically a fee on planet-warming carbon embedded in goods produced outside the 27-member bloc. The carbon border adjustment would be tied to Europe’s Emissions Trading System, which puts a price on carbon to incentivize companies to reduce their emissions. “It’s one of the most unbridgeable and challenging issues in this border carbon adjustment debate,” said Christopher Kardish, an adviser on carbon markets and pricing at the Berlin-based think tank Adelphi. “The increased attention globally around border carbon adjustments has captured the attention of lawmakers on both sides of the aisle,” he said. While the concept of a border carbon adjustment isn’t new, the E.U.