The European Union has a bold plan to make sure its own strengthened pollution standards aren’t undermined by trading partners with weaker ones. It’s introducing a levy known officially as the Carbon Border Adjustment Mechanism (CBAM) to combat so-called carbon leakage, which happens when companies shift production to places with laxer policies to reduce costs. The aim is to level the playing field and protect European manufacturers while prodding other regions to follow the EU’s lead on taxing emissions. The idea has triggered a hostile reaction from trading partners including Russia and China, and added to tensions over green subsidies with the US.