Under pressure from frequent flyers alarmed over climate change, the airline industry says it is "hellbent" on reducing emissions — but the technology needed to drastically reduce its carbon footprint is still out of reach.In recent months climate activists have stepped up efforts to convince travellers to boycott air travel, with Swedish schoolgirl and campaigner Greta Thunberg spearheading the trains-over-planes movement and making "flygskam", or flight shame, a buzzword