The Globe and Mail reports in its Monday edition that sustainability was a hot topic last week at the Paris Air Show, the world's largest event for the aviation industry, which faces increasing pressure to reduce the climate-changing greenhouse gases that aircraft spew. An Associated Press dispatch to The Globe says that even the massive orders at the show got a emissions-reduction spin: Airlines and manufacturers said the new planes will be more fuel-efficient than the ones they replace. Start-ups are working feverishly on electric-powered aircraft, but they will not catch on as quickly as electric vehicles. That means sustainable aviation fuel has become the industry's best hope to achieve its promise of net-zero emissions by 2050. Aviation produces 2 to 3 per cent of worldwide carbon emissions, but its share is expected to grow as travel increases and other industries become greener. Sustainable aviation fuel (SAF), however, accounts for just 0.1 per cent of all jet fuel. Made from sources like used cooking oil and plant waste, SAF can be blended with conventional jet fuel but for now costs much more. Delta Air Lines is being sued in U.S. Federal Court over its claims to be the world's first carbon-neutral airline.