Air Travel's Impact: Pollution-Free Skies

Aviation is a significant contributor to climate change, with airplanes burning fossil fuels that release carbon dioxide (CO2) emissions and other gases, such as nitrogen oxides, water vapour, soot, and sulfur aerosols, which have warming effects on the atmosphere. While aviation has become more fuel-efficient over the years, the overall emissions have increased due to the rising demand for air travel. As a result, the aviation sector faces the challenge of decarbonizing, which may involve reducing corporate and overall air travel, improving energy efficiency, and transitioning to low-carbon fuels and aircraft technology. With these considerations in mind, it is worth exploring what the state of pollution would be without air travel and its contribution to global emissions.

Air travel's contribution to global warming

Air travel is a significant contributor to global warming. While it accounts for only around 2.4% to 4% of global CO2 emissions, it is responsible for about 4% to 5% of global warming. This discrepancy is due to the impact of non-CO2 emissions, such as contrails (water vapour trails) and other atmospheric gases and pollutants. These non-CO2 emissions have a more substantial warming effect than CO2 alone.

The impact of air travel on global warming is especially notable given that only a small percentage of the global population flies regularly. In richer countries like the UK and the US, around half of the population flies in any given year, and only 12-15% are frequent flyers. This means that for those who take regular flights, air travel constitutes a considerable chunk of their carbon footprint. A return flight from London to San Francisco, for example, emits around 5.5 tonnes of CO2 per person, more than twice the emissions produced by a family car in a year.

The aviation industry has become more energy-efficient over the years, with a halving of the carbon emitted per passenger-kilometre between 1990 and 2019. However, this gain in efficiency has been counteracted by the quadrupling of passenger and freight demand over the same period. As a result, global aviation emissions have doubled from 0.5 billion tonnes in 1990 to 1 billion tonnes in 2019.

To reduce the climate impact of aviation, the most effective solution is to simply fly less. A sustained annual decrease in air traffic by 2.5% or a transition to a 90% carbon-neutral fuel mix by 2050 would halt aviation's contribution to further warming. Additionally, individuals can choose alternative modes of transport, such as trains or coaches, which are much lower-carbon means of travel than flying.

Alternatives to air travel

Aviation is a major contributor to global carbon emissions, with aircraft emitting around 357 grams of CO2 per passenger-kilometer in 1990, and this figure halving to 157 grams by 2019. While aviation has become more energy-efficient, the carbon intensity of the fuel has not improved, and alternatives like biofuels remain a tiny fraction of global demand.

With this in mind, what are some alternatives to air travel?

Firstly, ground transport options like trains, coaches, and even cars can often be more climate-friendly than flying for shorter distances. Trains, in particular, can be more convenient, dropping passengers off closer to city centers than airports, and offering the chance to explore new destinations along the way. They also provide more space to move around and enjoy the view.

For those seeking alternatives to commercial air travel, private jet charters have become an increasingly popular option since the pandemic. Private jets offer convenience, privacy, and a passenger-first approach, with the added benefit of flying into smaller regional airports and allowing passengers to determine their departure times. However, private jets are likely to be more expensive and may not be a feasible option for larger groups.

While giving up flying can be a challenging decision due to the freedom and cultural experiences associated with travel, exploring locations closer to home can be a surprising and environmentally conscious alternative.

The environmental impact of aviation biofuel

Aviation biofuel, also known as bio-jet fuel, sustainable aviation fuel (SAF), or bio-aviation fuel (BAF), is a type of biofuel used to power aircraft. The use of aviation biofuels is considered a key element in reducing the environmental impact of aviation.

Aviation biofuels are produced from various sources, including plant or animal sources such as Jatropha, algae, tallows, waste oils, palm oil, Babassu, and Camelina. They can also be derived from solid biomass using pyrolysis processed with a Fischer-Tropsch process (FT-SPK) or through an alcohol-to-jet (ATJ) process from waste fermentation. Additionally, synthetic biology through a solar reactor is another method for producing aviation biofuels.

In addition to reducing CO2 emissions, aviation biofuels offer further environmental benefits. They can significantly decrease the emission of pollutants such as sulfur oxides and particulate matter, which are commonly found in conventional jet fuel emissions. Additionally, aviation biofuels contribute to reducing contrail formation, which has a substantial impact on climate change due to its ability to trap greenhouse gases.

While aviation biofuels offer environmental advantages, there are also challenges and considerations. As of 2020, aviation biofuel was more expensive than fossil jet kerosene, and its economic competitiveness is marginally improved by certain exemptions from carbon compliance liability costs. Additionally, the compatibility of different engine types with biofuels requires further research and adjustments to ensure optimal performance and meet environmental targets.

In summary, aviation biofuels have a positive environmental impact by reducing CO2 emissions, decreasing pollutants, and mitigating the formation of contrails. However, the higher costs and technical challenges associated with their implementation need to be addressed to make aviation biofuels a more viable solution for the aviation industry's sustainability goals.

Aircraft noise pollution

Engine and mechanical noise is generated by the rotation of engine parts, most noticeable when fan blades reach supersonic speeds, resulting in a "buzzsaw" noise. Aerodynamic noise is caused by the airflow around the surfaces of the aircraft, especially during low-altitude, high-speed flight. Aircraft systems, such as the cockpit, cabin pressurization, conditioning systems, and Auxiliary Power Units (APUs), also contribute to noise levels, with the APU being a significant source of noise in commercial jet aircraft.

Helicopters and propeller aircraft produce noise from both aerodynamic and mechanical sources. The mechanical sources produce narrow-band, high-intensity peaks related to the rotational speed and movement of the aircraft's moving parts. In computer modelling, noise from a moving aircraft is treated as a line source. Aircraft gas turbine engines (jet engines) are particularly noisy during takeoff and climb, though advancements in noise reduction technologies have made the airframe noisier during landing.

Despite technological advancements leading to quieter airplanes, aircraft noise remains a concern for many communities. The Federal Aviation Administration (FAA) in the United States has been working to address these concerns through initiatives like performance-based navigation (PBN), which allows aircraft to fly more precise flight paths to reduce flying time, fuel use, and emissions. However, PBN has also been criticized for potentially concentrating aircraft noise over smaller areas. The FAA uses metrics like the Day-Night Average Sound Level (DNL) to assess the impact of flight paths on noise levels, but additional metrics and tools are needed to fully understand and address the issue.

The aviation industry's efforts to reduce emissions

Aviation is one of the fastest-growing sources of greenhouse gas emissions. In 1990, global aviation emitted around 0.5 billion tonnes of CO2. By 2019, this figure had doubled to around 1 billion tonnes. Despite improvements in energy efficiency, the carbon intensity of the fuel used has not changed.

To address these issues, the aviation industry has taken several measures to reduce its emissions and environmental impact. Here are some key efforts:

• Improving Energy Efficiency: The aviation industry has made significant strides in improving energy efficiency. Between 2010 and 2019, average fuel efficiency per revenue passenger kilometre (RPK) improved by over 2.5% annually. This improvement resulted from advancements in aircraft design and technology, the use of larger planes with higher 'passenger load factors', and a reduction in empty seats.
• Alternative Fuels: Airlines are exploring alternative fuels, such as biofuels and sustainable aviation fuels (SAFs). SAFs have gained attention due to their potential to reduce the industry's climate impact. Countries like France, Norway, and the United Kingdom have mandated SAF blending targets, and investments are being made to support the development and adoption of electric aircraft.
• Emissions Offsets: The aviation industry is investing in emissions offsets, both within and outside the sector. The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is a notable example, aiming to limit net carbon emissions from international flights between participating countries from 2021 to 2035.
• Innovation and Technology: The industry recognises the importance of innovation and technology in reducing emissions. Research and development activities focus on understanding the impact of non-CO2 emissions, such as contrails, and developing technological solutions. The European Commission's Innovation Fund supports projects related to mitigating non-CO2 effects, enhancing scientific understanding, and assessing policy measures.
• Policy and Regulatory Changes: Governments and organisations are implementing policies and regulations to reduce aviation emissions. The European Commission has set an intermediate target of a 55% reduction in GHG emissions by 2030 and is amending the EU Emissions Trading System to phase out allowances for the aviation industry. ICAO member states have also adopted a long-term aspirational goal of achieving net-zero carbon emissions from international aviation by 2050.

While the aviation industry has made efforts to reduce emissions, it remains a challenging sector to decarbonise. The continued reliance on jet kerosene-powered aircraft and the lack of widely adopted low-carbon alternatives contribute to this complexity. However, with ongoing advancements in technology, policy support, and a growing focus on sustainability, the industry is taking steps towards a more sustainable future.

Frequently asked questions