Touted to contribute about 2-3% of global CO2 emissions, the aviation industry produces around one billion tonnes of carbon dioxide annually on a global scale, which is equivalent to what Japan, the third-largest economy in the world, produces.
Air travel is technologically based on outdated practices, when compared to the fact that many governments are controlling emissions from cars and trucks, such as by gradually phase-out internal combustion engines and moving to electric vehicles. Except for a break during the COVID-19 pandemic, annual increases in aircraft emissions have averaged 2.5% over the past 20 years.
The industry’s influence on global warming is expected to surpass that of its whole history, which dates back to the Wright Brothers’ pioneering flights in the early 1900s, over the next 30 years.
All emission sectors must decarbonize and show routes to net zero emissions in the second half of the 21st century if global warming is to be kept far below 2 °C (Intergovernmental Panel on Climate Change 2018). International aviation is frequently excluded from reduction targets, such as those in the Paris Agreement, as it is generally regarded as a “hard to abate” industry (UK Climate Change Committee 2020, Grewe et al 2021)
Climatic effects of aircraft
Before the epidemic, aircraft engines burnt more than 1 billion litres of fuel each day from 2016 to 2019. They produce up to 15.14 g of NOx, 1.2 g of SO2, 3.16 kg of CO2, 1.23 kg of water vapour, and 0.03 g of black carbon (soot) per kg of fuel.
Nitrogen oxides react in the atmosphere, changing the radiative balance of other gases such as stratospheric water vapour (H2O), ozone, and methane (CH4). This has an indirect effect on climate. This additional net warming effect is brought on by these non-CO2 emissions.
The biggest unknown is cloud formation, a rapidly changing element with enormous uncertainties. According to certain simulations, “contrail cirrus” may have contributed to warming up until 2018 almost twice as much as CO2 from the aircraft industry. Due to these additional consequences, biofuels may not completely solve the climate problem even if they replace traditional jet fuels and lower CO2 emissions.
Does it end there? Perhaps not.
This brings up a second major issue related to investment planning. Governments and corporations can’t attempt to treat the patient if the diagnosis isn’t apparent. If contrail cirrus turns out to be a significant issue, then alternatives to clean fuels, such as other propulsion systems and possibly rerouting planes, will need to be considered.
Since certain atmospheric conditions are required for the formation of contrail cirrus, changes to flight times, altitudes, and routes could theoretically be important. The aviation industry must exert greater independent effort to reduce climate impacts if carbon offsets do not genuinely offset at scale or if the use of clean fuels does not increase.
The limited vision of airlines/stakeholders
Airlines frequently have very slim profit margins. Airports face concerns of stranded costs as a result of quick technological advancements while trying to recoup the cost of significant infrastructure investments. Additionally, every time they create a completely original plane, like the Boeing 787 or the Airbus A380, aircraft makers “bet the company.” Large companies that are concerned with risk and cost are in charge of many parts of the aviation industry. The least disruptive technology options are what they seek.
The way forward
Sustainable aviation fuels may play a significant role, but much more funding is required for choices that are not now economically feasible, such as electric or hydrogen-powered aircraft, which may prove to be successful methods for cutting emissions and minimising contrails. Those solutions are unlikely to emerge from the mainstream industry due to their disruptive nature.
Fuel economy will be important, but it is unlikely to significantly lower emissions. The industry already has financial incentives to get more passenger miles out of each tonne of expensive jet fuel, but improvement rates are unlikely to be much higher than 1% annually.
A more broad experimental strategy is required, one that makes investments in a range of response options, such as energy, hydrogen, and cleaner, more scalable fuel alternatives. Europe would likely be at the forefront of it because its climate regulations are already robust and credible and because European governments can support financially and technologically hazardous ventures.
The European air traffic management system is focusing on determining which routes are best for the environment since shorter routes with fewer delays can reduce the demand for fuel and new routes can reduce contrail creation.
The initiative by Norway to develop a market for short-haul electric aircraft is a good illustration of a partnership between businesses and governments that aims to invest in disruptive technologies. Many of the airports in Norway, a small nation divided by fjords and mountains, are built for quick takeoffs and landings and have proximity to one another.
As a result, Norway makes an ideal test location for electric aircraft, and since few of these routes are economically viable, the government can stipulate in bidding specifications that zero-emission flights be included.
Furthermore, research is crucial to advancing our understanding of topics like contrails and chemical interactions in the atmosphere, which will allow the aviation sector to move forward with more assurance. Understanding how various propulsion systems affect the climate through atmospheric chemistry needs to be improved, as does the theory and measurement of how aviation generates contrails, cirrus, and other induced cloud changes.
For instance, hydrogen-fueled aircraft may release H2 gas into the atmosphere during production and transport while continuing to emit nitrogen oxides and contrails, both of which may have unknowable effects on the climate.
It is impossible to reduce aircraft emissions by merely installing new pollution-capturing equipment. The ability to create adequate quantities of clean aircraft fuel could prove to be unachievable.
And in an industry that is particularly concerned with safety, weight, and space, addressing the additional climatic consequences of aircraft beyond CO2, such as contrails, may necessitate overhauling engines, airframes, and onboard storage. Several million different parts make up a conventional aeroplane. Air traffic control and ground handling procedures are likewise closely entwined with commercial aviation, making it challenging to design and implement significant changes.
The risks that aviation encounters must be taken carefully. The International Civil Aviation Organization (ICAO) is holding its triennial assembly this month in Montreal, Canada, and a top priority on the agenda is reducing the sector’s contribution to global warming. An industry-wide target for reducing emissions in keeping with the objectives of the Paris climate agreement will be negotiated by ministers from 193 countries.