table of contents to seek an international solution through icao and that will allow the u.s . secretary of transportation to prohibit u.s . airlines from participating in the ets . ultimately , the scope and application of ets or other emissions trading schemes to our operations , now or in the near future , remains uncertain . similarly , within the u.s. , there is an increasing trend toward regulating ghg emissions directly under the caa . in response to a 2012 ruling by the u.s