The outcome of the 15th conference of the Parties to the UNFCCC in Copenhagen showed a shift from a top-down approach with a collective target favoring environmental objectives to a bottom-up accord favoring political feasibility. There is no meaningful binding agreement in sight, also because the global climate regime and the global trade policy regime appear to be on a collision course. Following a review of the challenges ahead, the paper argues that trade will have a second-order contribution to world-wide CO2 emissions. Evidence shows increasing carbon transfers through trade, but the magnitude of carbon leakage effects may be less than feared in some circles. Trade policy, however, will play a role in implementing climate mitigation policies in three areas: maintaining an open trading system and hence boosting growth and facilitating technology diffusion; leveling the playing field for countries that do not mitigate and as a strategic instrument to bring compliance and participation. The paper concludes that a climate agreement with a few guiding principles and leeway where much initial mitigation would first take place unilaterally or in small groups, as under the early days of the GATT, is the most promising way ahead. This would help preserve an open trading system as well as environmental integrity.