Sharply divergent climate change policies on opposite sides of the Atlantic are setting off political fireworks as European environmental regulators prepare to extend their reach across the ocean. Starting Jan. 1, the European Union will require all carriers entering or leaving its airports to either reduce their emissions or pay a charge — whether the airline is United, Air France or Lufthansa.

Until now, the United States and Europe have taken a to-each-his-own attitude on how to handle the greenhouse gas emissions that contribute to global warming, leaving American consumers largely immune to aggressive European environmental regulation and its costs. But come 2012, Americans flying to Europe are likely to be paying indirectly for the emissions their trips create — chiefly through steeper fares, although uncertainty persists about how much higher they will be.

American carriers and air freight companies will also face a new type of competition, because the “cleanest” airlines will pay less in emissions fees.

The United States airline industry has fought aggressively against inclusion in the European Union Emissions Trading System, most recently in a lawsuit filed before the European Court of Justice, the European Union’s highest court. It argues that the European Union has no legal right to regulate American carriers or flight emissions that are released over other countries or into international airspace as planes make their way across the ocean. A ruling is not expected until late this year at the earliest.