This Policy Brief assesses the evolving EU Emissions Trading System and EU carbon border adjustment mechanism (CBAM) and explains objections within Europe and from major trading countries likely to be affected by the proposed CBAM import levies. While EU officials have sought to ensure that the CBAM is consistent with obligations under the World Trade Organization (WTO), key aspects of the CBAM could violate WTO rules and are likely to be contested, taking years to play out. Meanwhile, several other countries will adopt new carbon-inspired border restrictions, adding to global trade frictions. Major carbon-emitting countries, therefore, need to act cooperatively instead of unilaterally to both advance the fight against climate change and update the rules-based global trading system. Two-thirds of greenhouse gas emissions result from nontraded activities, such as road transport, electricity generation, and home and office heating. Countries can curb emissions in these activities, while developing guidelines for carbon abatement in traded sectors.