The European Union reiterated that it will consider exempting inbound flights from its emissions trading system (ETS) if the U.S. implements equivalent market-based measures. Until then, the EU will continue to include international flights in the ETS, Siim Kallas, vice president of the European Commission, and Connie Hedegaard, commissioner for climate action, wrote in a Jan. 16 letter obtained by Aviation Week.

The letter responds to one sent on Dec. 16 by Secretary of State Hillary Rodham Clinton and Transportation Secretary Ray LaHood threatening “appropriate action” if the EU pressed ahead with its plan to include aviation in the ETS.

“We see the inclusion of aviation in the EU ETS as an important contribution to, and a catalyst toward, global action rather than as an obstacle,” Kallas and Hedegaard wrote. The letter acknowledges U.S. claims that sustainable fuel and improved engine technology have a role to play in carbon mitigation, but insists on the necessity of market-based measures, such as the ETS. “ICAO has long recognized the role market-based measures can play in achieving environmental goals cost efficiently and in a flexible manner.” (See related story).

Kallas and Hedegaard also reiterated the EU’s belief that the ETS conforms to international law.

The EU remains committed to working with the U.S. to find mutually acceptable ways to exempt U.S. flights, and through ICAO to find a global system, the letter says. “Both sides must demonstrate their readiness to work hard together, both bilaterally and of course with ICAO partners to reach a multilateral agreement tackling aviation emissions,” Kallas and Hedegaard write.