Read the given passage and answer the questions that follow.
Several major airlines have pledged to reach net-zero carbon emissions by mid-century to fight climate change. It’s an ambitious goal that will require an enormous ramp-up in sustainable aviation fuels, but that alone won’t be enough, the latest research shows. The idea of jetliners running solely on fuel made from used cooking oil from restaurants or corn stalks might seem futuristic, but it’s not that far away. Airlines are already experimenting with sustainable aviation fuels, including biofuels made from agriculture residues, trees, corn and used cooking oil, and synthetic fuels made with captured carbon and green hydrogen. United Airlines, which has been using a blend of used oil or waste fat and fossil fuels on some flights from Los Angeles and Amsterdam, recently announced plans to power 50,000 flights a year between its Chicago and Denver hubs using ethanol-based sustainable aviation fuels by 2028. The airline also launched a US$100 million fund on 21 February 2023, with Air Canada, Boeing, GE Aerospace, JPMorgan Chase and Honeywell to invest in sustainable aviation fuel start-ups to expand the industry.
What is the tone of the speaker?