Reuters: Four of the world’s top airlines have backed a global scheme to curb carbon emissions and hope the proposal will be included in a broader U.N. pact to fight climate change. It is the first time airline firms have banded together to make recommendations to U.N. climate change officials on how to tackle the sector’s carbon emissions. Aviation is responsible for about two percent of global greenhouse gas pollution and that share is expected to rise, as leading green groups and the …