Green 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.
By 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 fuel-efficient 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.
On Ground Challenges
At present, there are two significant challenges with SAF. First, it is available today in only small and expensive quantities: 0.1% of current fuel demand, and costing several times more than conventional jet kerosene. It may reach 2% of demand by 2030, and, with regulatory support, 10% in specific markets such as Europe.
Second, the future potential of biomass-based SAF is constrained. Other users, notably ground and maritime transport, also compete for biofuels. They might be squeezed out by aviation’s greater need, but likely only by higher prices. Once all suitable waste is allocated to make bio-based SAF, further volumes need specially-grown crops – competing with food production and natural ecosystems, and requiring water and fertiliser. It appears technically possible to meet all 2050 air travel demand with bio-SAF, but likely not desirable from environmental, social and economic viewpoints.
Going beyond this will require hydrogen, liquid ammonia, or synthetic fuels made using atmospheric carbon dioxide. These promise long-term solutions but need cost reductions and much technological development in fuel production, logistics and engines.
So one complement is low-carbon aviation fuel (LCAF). These are derived from petroleum, are identical to traditional fuel, and create the same emissions when used. But they are produced and processed to minimise life-cycle emissions.
Not all crude oils are equal. Those that are high in sulphur, heavy (high-density), come from mature fields, or whose associated (by-product) natural gas is burnt off rather than being used productively, are more carbon-intensive to extract and refine.
Carbon footprints of crude oil production vary widely between countries: As found by researchers from Stanford University published in Science, from 20-180 kilograms of carbon dioxide equivalent per barrel between the best and worst cases worldwide (a barrel of oil weighs about 380 kg). Differences between individual companies and fields can be even larger. The best performers are some Middle East countries with giant, highly-productive fields, and environmentally-minded nations such as Denmark and Norway.
Oil companies have a wide variety of tools to reduce their carbon footprint: being selective about which fields they develop; stopping flaring and leaking of unwanted gas; improving energy efficiency; powering operations with renewable energy; using low-carbon hydrogen in their refineries; and employing carbon capture and storage (CCS) to prevent carbon dioxide escaping into the atmosphere.
Eventually, companies such as Occidental Petroleum hope to produce “carbon-neutral oil”, where they capture an equivalent quantity of carbon dioxide directly from the atmosphere to inject into their oil-fields to enhance production.
Globally, traditional jet fuel has an average life-cycle carbon intensity of 89 grams of CO2 per megajoule whereas LCAF certified under the Carbon Offsetting and Reduction Scheme for Aviation (CORSIA) must have a carbon intensity of below 80.1 gCO2 per MJ, i.e. at least 10% lower.
Current best-in-class operations in both production and refining would deliver about a 12% reduction over the average. So LCAF can realistically be available in significant volumes and at only moderate added cost over the next decade. Along with efficiency gains, it can therefore play a major role in meeting the aviation industry’s medium-term targets, while truly near-zero carbon options scale up.
To achieve this, airlines should recognise the potential of LCAF to meet their compliance obligations and interim corporate emissions targets. They should work with their fuel suppliers to demand and certify LCAF. In turn, the oil industry will respond by valuing its lower-carbon operations more highly and bringing in low-emissions technologies such as renewables and CCS. By solving the chicken-and-egg problem of matching low-carbon fuel demand and supply, the industry can buy crucial time – and escape some political heat.
(The writer is CEO of Qamar Energy, and author of ‘The Myth of the Oil Crisis’.)
Image: Honeywell Aerospace
