Carbon offsetting is one of the main ways airlines attempt to “neutralise” their emissions. Many airlines (e.g. EasyJet, Ryanair, British Airways) argue that their emissions are partly or fully compensated through investing in projects that mitigate carbon emissions. However, the EU Commission found that up to 85% of offsets under the UN Clean Development Mechanism did not fully deliver claimed emission reductions. In addition, one of the most popular forms of offsets – tree planting – is limited and should be used to make up for the lost time in terms of climate action.
The market for carbon offsets continues to grow in both the compliance and voluntary sectors. In compliance markets, entities can purchase and trade offsets to comply with legal emissions caps. Firms, individuals, and other groups typically sustain the voluntary markets, often pursuing net-zero or low emissions goals. Carbon offsets tend to support renewable energy ventures, energy efficiency projects, or carbon removal efforts – although to what extent and how successfully those goals are achieved remains highly questionable.
The indirect and multifaceted nature of offsets makes them challenging to account for, and it is often difficult to measure the impact any one carbon offset may have. In addition, the voluntary offset market shifts attention away from present-day issues and innovations, ultimately weakening the drive for a zero-carbon future. Thus, carbon offsetting cannot be recommended as a best practice, especially considering that customer willingness to pay remains very low.
If a carbon offset must be considered, the offset measure must meet several critical criteria to ensure it is, at a minimum, not additionally harmful.
- The offset must meet the principle of additionality. Under additionality, we must ask, “Does this offset lead to a reduction in emissions that otherwise wouldn’t have been undertaken“? Essentially, would the project go ahead without the money from the offset? If the answer is yes, the offset is not a valid offset of emissions as it does not lead to additional emissions reduction. The principle of additionality requires rigorous outside accounting and is a high bar that often cannot be met.
- Offsets must result in a permanent reduction in carbon levels. Suppose offsets do not result in a permanent reduction of greenhouse gas emissions. In that case, they are essentially counterproductive – reduced emissions must be gone for good for an offset to be effective.
- Offsets must address leakage, whereby the protection of one area results in the overuse of another, and thus emissions are not truly reduced. For example, if an offset protects one area of forest from deforestation, it must also ensure that other forested areas are not stripped due to those protections.
- The offset must not be double counted. Registries must be meticulously kept and ensure an offset is counted for its entire life-span. Given the already contentious accounting of an offset’s emissions reductions, ensuring emissions are not double-counted remains a thorny issue.
Offsets can be counterproductive if they create the false impression among consumers that the comparably low price of tCO2eq purchased as an offset fully neutralizes the negative impact of the flight on the environment and thus encourages an increase in activity levels.
Drastic scaling up sustainable aviation fuels is necessary to impact decreasing emissions. However, it is not certain that biofuels are the best alternative in the long term. Currently, biofuels make up only 0.01% of all aviation fuel globally. While some research has shown that biofuels from organic matter and live plants are more compatible with modern jet engines than fossil fuels, their scaleability has a significant problem. While technologies for the production of sustainable biofuels already exist, scaling up in a way that would not have a destructive impact on the environment is currently not feasible. Therefore, biofuels must meet stringent sustainability criteria, which current crop-based biofuels do not meet. As such, crop-based biofuels should not be supported at this time as a sustainable alternative.
Synthetic aviation fuels are an option to reduce dependency on fossil fuels in aviation. An example of synthetic fuel is e-kerosene or PtL (power-to-liquid). Fuel producers can blend it with regular jet fuel to bring down overall flight emissions, and it has been shown to potentially decrease emissions by up to 80%. In addition, e-kerosene is generally more sustainable than other fuel alternatives, such as those made from biomass or crop-based fuels. Synthetic fuel production currently accounts for only 0.1% of the jet fuel market and faces the challenge of high start-up costs and the need to scale production. Current production processes are highly energy-intensive, requiring large amounts of CO2 and electricity.
Blending mandates, which would require a specific amount of synthetic fuel to be mixed with standard A-1 jet fuel for flights in the future, could spur production by guaranteeing a certain level of consumption by airlines and other industry groups. Additionally, mandating demand will help drive the price of e-kerosene down, addressing another implementation issue.
ICAO has set up an Alternative Fuels Task Force, which predicts that it is possible for the aviation industry to entirely switch to low-emission fuels by 2050, resulting in an emissions reduction of 63%. However, it would require unprecedented levels of investment. Thus, other additional measures deterring unnecessary air travel must complement sustainable fuel policies.
In its “fit for 55” package from July 2021, the European Commission proposed a blending mandate beginning in 2025, which would require 2% of all jet fuels to be sustainable, climbing up to 63% by 2050. The proposal includes a sub-mandate which would require e-kerosene to account for 0.7% of all jet fuel purchases in the EU by 2030. The EU airports would be required to implement the necessary infrastructure to store and blend the fuels to meet the mandate.
In 2021, Atmosfair, a climate organisation in Germany, opened a plant producing e-kerosene made from sustainable materials in northern Germany. It uses materials including CO2 captured from the air and a biogas plant that runs on food waste and energy from local solar and wind projects to produce e-kerosene. Current production is at eight barrels (one ton) per day of crude paraffin, which is then refined into A-1 jet fuel and sent to Hamburg Airport.
Hydrogen offers a viable option to reduce emissions from the aviation sector, either as power in a fuel cell or through combustion. However, despite recent technological improvements, there are still significant limitations to the feasibility of hydrogen in the near term.
Hydrogen is gaseous at normal atmospheric pressure and temperature. It has to be liquified to store it in large enough amounts to use as fuel, which requires very low temperatures (hydrogen becomes liquid below -252.87ºC). Liquid hydrogen has greater energy by mass but only around a quarter of the energy density of regular jet fuel. Storage tanks for liquid hydrogen are complex and heavy and, as a result of the density problem, need to be about four times the size of a standard fuel tank to deliver the same amount of energy. This creates a significant engineering question for aeroplane manufacturers and airlines, who loathe sacrificing seats (and revenue) for fuel tanks.
Additionally, fuel-cell options are not particularly well suited for aircraft at this point. Although hydrogen fuel cells can be quickly recharged and adapted for use on the ground, they would be far too heavy for aircraft applications. Hydrogen fuel cells’ initial development for ground technology makes adjusting them to flight challenging in the short term. However, for short-haul aviation, smaller planes can be powered by hydrogen.
Engineers have proposed hybrid solutions to solve the problems presented by hydrogen-only systems. Such systems would use a combination of hydrogen and combustion to power flights and could potentially give planes a greater range than just hydrogen combustion or fuel cells alone. Hybrid hydrogen-electric systems are likely to be the most common, using electric propulsion and hydrogen fuel.
Finally, the economic question currently puts the feasibility of hydrogen planes in a tight spot. Hydrogen production using today’s technology is highly expensive (around USD 6/kg when produced by electrolysis from renewable sources). It would need to drop to under USD 2/kg to compete with conventional fuel, which typically sits below USD 1/kg. Fuel-cell aircraft would only be economically viable when the price of hydrogen fuel is competitive against conventional fuels.
Airbus is currently aiming to introduce the world’s first commercial hydrogen plane by 2035 and has three different models of hydrogen planes proposed, all driven by hybrid-hydrogen engines.
Zeroavia already has two hydrogen-powered planes for up to 6 passengers.
Electric ground support
While the electrification of aeroplanes constitutes an issue, electrification of all vehicles and equipment used at the airport constitutes a viable option to reduce emissions from this challenging sector. Airport ground support equipment (GSE) includes vehicles necessary to the functioning of an airport, such as tugs and tractors or busses – all of which are commonly run on diesel.
However, there has been a shift to battery powered electric GSE (e-GSE), which contributes to a reduction in on-site carbon emissions. In addition, GSE is particularly suited to electrification due to the nature of the work – airport ground support is full of starts and stops and pushing and pulling over short distances, which is excellently served by the low-end torque generated by electric engines. Electric charging stations are safer than diesel pumps and can be placed in more locations around the airport, facilitating easy charging.
E-GSE additionally help to reduce particulate matter in the air, are quieter, and reduce energy costs overall, leading to a more healthful, quiet, and efficient work environment for ground support staff. The most common GSE already have electric alternatives, and diesel-electric conversions are relatively common. By transitioning all GSE to electric power, significant emissions and energy savings can be made in the air transport sector while also increasing reliability and flexibility among the GSE fleet.
Amsterdam Schiphol Airport designed and implemented electric ground support units (GSU) in association with Nissan and ITW GSE as a part of their ‘Smart and Sustainable’ action plan to reduce airport emissions. These units provide power to aircraft located on the apron and charge electric ground support vehicles using already existing battery technology most commonly used in cars. Compared to diesel GSE and earlier GSU, the e-variants reduced carbon emissions by 90% and NOx emissions by over 95%. In addition, Amsterdam Schiphol uses e-GSE such as busses, pushback trucks, and stairs as part of their goal to become carbon neutral by 2030.
Singapore Changi Airport uses over 80 electric baggage tractors supported by a shared pool of charging stations to facilitate ease of use and support further electrification. One terminal already has an entirely electric fleet which has saved 627 tonnes of carbon emissions to date, and the Changi Group plans to transition all terminals to all e-GSE by 2030 with the support of its ground service partners.
Ostensibly to protect competition and primarily to allow for efficient coordination of takeoffs and landings, slot rules were instituted, which apply to most large European airports. Also called the ‘use-it-or-lose-it’ rule, airlines are allocated a certain number of takeoff or landing slots and must use at least 80% of those slots to qualify for the same number of places in the next scheduling season (so-called 80/20 rule). If airlines do not meet the 80%, unused slots are put back in the slot pool for reallocation to another airline for the next scheduling season.
To avoid losing the slots, in some cases, airlines have resorted to flying so-called ‘ghost flights’ (flights which are empty or unprofitable). Although previously suspended, the 80/20 rule was reinstated at the 64% level at the end of 2021, leading to an estimated 18,000 empty or near-empty flights by the Lufthansa group (which includes Swiss, Brussels Airlines, Austrian Airlines, and Eurowings), which they claim was due to the reinstatement of the rule at the 64% level. The United Kingdom’s Civil Aviation Authority reports that in 18 months from March 2020, almost 15000 empty or near-empty flights left the United Kingdom.
This rule creates a situation in which airlines feel they must maintain their slots at any cost, leading to unnecessary emissions, threatening emissions reduction goals and contributing to the climate crisis. To address this situation in the short term, governments should abolish the 80/20 rule or decrease the requirement to use the landing slots significantly, thereby removing the incentive to fly empty planes. Suppose the rule is abolished, or the usage requirements decreased. In that case, airlines will be free to cancel less full or empty flights without concern for losing their slots, enabling them to operate just as many flights as are necessary and with an increased load factor.
The Worldwide Airport Slot Board recommends a continuation of ‘Justified Non-Utilisation of Slots’ (JNUS) rules. Airlines can protect their slots even when not using them due to extenuating circumstances related to COVID-19. A potential area for expansion would include JNUS exceptions for climate reasons, enabling airlines to protect their landing slots without the use of ‘ghost flights’.
An improvement in planes’ energy efficiency could significantly reduce emissions from this mode of transport and make it easier to ramp up the utilisation of alternative fuels.
Currently, engineers typically improve fuel efficiency in one of two ways:
- Redesign the plane from the ground up, improve aerodynamics, use lighter materials, fabricate better engines. When applied to Boeing Dreamliner 787, it improved energy efficiency by up to 27%.
- Increase the fuel efficiency of the engines, which can decrease the plane’s energy consumption by around 10%.
Overall, very small and very large planes tend to lag in fuel efficiency compared to the more common twin-engine widebody aircraft like the Boeing 787. Although massive quad-engined planes were previously necessary to make ultra-long-haul and transoceanic flights, improvements in range and efficiency have allowed twin-engined aircraft to take on the longest routes with less fuel. Therefore, when possible, airlines should phase out heavy, inefficient quad-engine planes in favour of the lighter and much more efficient twin-engined planes.
An additional strategy to reduce emissions when flying is to address inefficiencies in air traffic control to reduce traffic jams in the air and on the ground. Traffic control can achieve this in three ways:
- Improving routes to be the most efficient possible.
- Managing departure queues, so planes (and travellers!) don’t sit on the tarmac for long periods burning fuel,
- Managing traffic so that planes can land with minimal wasted distance
The above measures can be achieved by close cooperation between all associated authorities to communicate constraints or congestion quickly can all help reduce fuel wastage. Additionally, flight planning can significantly impact fuel demand – for example, headwinds may make the most direct route more fuel-intensive than a longer route with a tailwind. Contrails generally form where it is humid and cold and can change how radiation enters and leaves the earth – a critical component of the greenhouse effect. A 2020 study modelled the Japanese airspace and found that just 2% of all flights contributed 80% of the contrail warming effect and that by changing routes, this impact could be reduced by 60%.
Both Airbus and Boeing have continued to improve the efficiency of their planes. The Boeing 787-9, 777, and Airbus A330 operate at above-average efficiencies, with ongoing improvements to efficiency every year. The airline industry has generally been supportive of this as well. For example, Qantas uses the Covid-19 pandemic and unprecedented drop in demand to accelerate its shift away from the Boeing 747 and the 787 and Airbus A321neo as part of their goal to reach net-zero emissions.
Within the EU, Eurocontrol and the German Aerospace Institute participate in an ongoing trial that tests the feasibility of avoiding creating contrails by shifting routes and other operational methods. Additionally, the Perfect Flight Project run by Finnair and Finntraffic Air Navigation Services aims to optimise flight paths to reduce environmental impacts using a data-driven methodology. The goal is to use this in cooperation with a global panel of indicators and international aviation authorities.
The United States Federal Aviation Administration (FAA) is implementing the Next Generation Air Transportation System (NextGen) to upgrade the current airspace management system and to mitigate the environmental impact of flying. The NextGen program has built new metrics and tools to measure noise and carbon pollution produced and funded scientific inquiry into alternative fuels and efficiency improvements.