THE ROAD TO ZERO CARBON AVIATION

The road to net-zero carbon is now clear in most sectors of the world economy-bar one relatively small, but crucial and fast-growing area. Air travel attracts heavy criticism for its planet-heating emissions. With game-changing technologies still on the far horizon, aviation needs ways to cut its carbon footprint now.

- ROBIN M. MILLS

Aeroplanes release about 2.1 per cent of humankind's carbon dioxide. But their injection of water vapour and other indirect greenhouse gases into the stratosphere, and the formation of condensation trails, worsen climate impact to 4.9 per cent of additional heating.

The airline industry aims to have no net growth in emissions from 2020 onwards, and to reach net-zero by 2050. Without action, pre-pandemic emissions were forecast to rise as much as 4.3 per cent per year over the next two decades. The International Civil Aviation Organization believes better operations and more fuelefficient planes could deliver 1.37 per cent savings per year-still leaving a large gap to aspirations, and to the acceptable levels implied by the Paris Agreement of 2015.

Other transport modes such as rail certainly can and should be used more. But they are impractical over oceans or intercontinental distances, remote communities or for time-sensitive cargo. Batteries may be suitable to power short flights but their weight is prohibitive for long-haul.

So for now, the industry is betting on sustainable aviation fuel (SAF). This is chemically similar to traditional jet fuel (kerosene), and so is compatible with current engines and fuel delivery systems. Today, it is made from biological materials such as waste cooking oil, food scraps, paper, and potentially in future wood, specially-grown plants and algae. It reduces carbon emissions by up to 80% compared to petroleum-based jet fuel.