Flying Planes at Different Altitudes Makes Aviation Less Bad for the Planet: Study
Mon, April 19, 2021

Flying Planes at Different Altitudes Makes Aviation Less Bad for the Planet: Study


Aviation has become more popular and commonplace throughout the years. Airline industry trade association The International Air Transport Association shared that there were a record-breaking 4.1 billion people who flew in 2017 and that the majority of these air passengers were from the Asia-Pacific region. However, just as the aviation industry continues to boom, unregulated carbon pollution from air transport has also become the fastest-growing source of greenhouse emissions.


Environmental impact of aviation

Air travel leaves a big environmental footprint not just because it uses fuel to power the airplanes for their trips that cover thousands of miles but also the trail of condensed water called contrail that is produced by the aircraft engine exhaust or changes in the air pressure. This is contributing to the warming of the planet. For this reason, efforts to change the design of the aviation engine have been made to reduce the CO2 emissions of air travel.

A team of researchers from Imperial College London said that flying airplanes at different altitude can make aviation less bad for the planet.  


Cutting the climate impact of aircraft contrails

In a new study titled “Mitigating the Climate Forcing of Aircraft Contrails by Small-Scale Diversions and Technology Adoption,” which appeared in the American Chemical Society journal, the authors explained that diverting some flights to slightly lower or higher altitudes than where they usually fly could lessen the climate impact of aircraft contrails.

Contrails are formed because the cold low-pressure air from around the aircraft meets the warm engine exhaust. When that happens, water vapor will freeze and condensation will be formed in the clouds. Although the aircraft contrails don’t last long, either just hours or a few minutes depending on the humidity level, it already creates an environmental consequence. For example, contrails cause radiative forcing.



Radiative or climate forcing

Radiative forcing is also called climate forcing. It is the difference between the insolation that is absorbed by the planet and the energy that is radiated back into space. This means that heat is prevented from being released into the atmosphere, warming the air below. A previous study has likewise suggested that the impact of contrails is greater compared to the carbon emissions from all airplanes combined.

Imperial College London’s lecturer on transport and the environment Marc Stettler said via business media brand Fast Company that the contrails may be short-lived, but their effect is stronger “during the time that they exist.” The fact that contrails are short-lived also means that the aviation industry can cut their environmental impact.


Focusing on the contrail-forming region

Stettler and colleagues discovered that altering a few thousand flights every day to a different altitude, either 2,000 feet lower or 2,000 feet higher, can lessen the effects of contrails up to 59%. The reason is that contrails are not forming in all areas above the clouds. It requires cold temperatures and high humidity conditions for contrails to be formed. These conditions are what create the “contrail-forming region.” They also found that the contrail-forming regions are thin and so making small changes in the altitude in certain flights can mean contrails will not be formed or it will not last long as compared in the present.

To come up with these findings, the team said that they used Japan’s airspace computer stimulation. Only 2% of the flights in the world were responsible for about 80% of the airspace radiative forcing, they added. If the aviation industry will focus on altering the flight altitudes, it could lead to about 60% drop in the climate impact related to contrails.



Stettler said further that although it is more fuel-efficient to fly airplanes at higher altitudes, reduction in the formation of contrails can more than just offset CO2 emissions from that fuel. Some planes today are also designed with more efficient engine combustion in a way that they lessen aviation contrails. The researchers added that technology advancement along with small changes in the flying altitude can reduce the harm of contrails by around 90%.

This does not mean instantly making air travel eco-friendly but it is already a “big step” toward that effort. The authors believed that the aviation industry still has to address carbon dioxide emissions, sustainable airplane fuels, and efficient flight routing.


Aviation pollution: facts and statistics

According to the Air Transport Action Group (ATAG), an independent coalition of organizations and companies in the air transport industry, global flights produced about 915 million tons of carbon dioxide in 2019. In the same year, humans produced more than 42 billion tons of CO2 globally. The world’s airlines likewise carried 4.5 billion passengers. Global aviation and related tourism have created more than 65.5 million jobs and 10.2 million of these are directly in the aviation industry.

Jet aircraft in the service nowadays is more than 80% fuel efficient per seat kilometer compared to the jets used in the 1960s. Sustainable aviation fuels (SAF) and other alternative fuels have been identified as excellent choices to help achieve climate targets in the aviation industry. Furthermore, around 80% of the CO2 emissions from aviation are emitted from flights of more than 1,500 kilometers with no practical alternative mode of transportation.

Meanwhile, the International Air Transport Association published the passenger numbers by region as follows: Asia-Pacific (1.5 billion passengers, 36.3% market share), Europe (1.1 billion passengers, 26.3%) North America (941.8 million passengers, 23%), Latin America (281.1 million passengers, 7%), Middle East (216 million passengers, 5.3%), and Africa (88.5 million passengers, 2.2%).



The top domestic routes were also found in the Asia-Pacific region. These busiest domestic airline routes are as follows: Hong Kong International Airport to Taipei Taoyuan (5.4 million passengers), Jakarta Soekarno-Hatta to Singapore Changi (3.3 million), Bangkok Suvarnabhumi to Hong Kong International Airport (3.1 million), Kuala Lumpur to Singapore Changi (2.8 million), and Hong Kong International Airport to Seoul Incheon (2.7 million). The rankings were dominated by two airports, Hong Kong International Airport and Singapore Changi.

The busiest airlines that fly the most in the US are American Airlines (324 million passengers), Delta Air Lines (316.3 million), United Airlines (311 million), Emirates (289 million), and Southwest Airlines (207.7 million).

Air traffic is increasing faster than before, particularly in the Asian markets, but this can also mean that greenhouse gas emissions will worsen. The aviation industry must do its part to curb climate change impacts.