EMISSIONS, EXPLAINED

Greenhouse Gas Emissions

Greenhouse gas emissions (GHG) encompass the total sum of emissions of various gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases are released into the atmosphere as a result of human activities such as burning fossil fuels, deforestation, and agricultural practices.

The issue with greenhouse gases is that they have the ability to trap heat in the Earth's atmosphere. As more GHG emissions are released, more heat accumulates in the atmosphere, leading to changes in the Earth's climate system. These changes include rising global temperatures, sea level rise, and an increase in the frequency and intensity of extreme weather events.

Additionally, it is worth noting that different greenhouse gases have varying capacities to cause warming, and they persist in the atmosphere for different lengths of time. To facilitate a standardised measurement of GHG emissions, a metric called "carbon dioxide-equivalents" or CO2eq is used. This metric attempts to combine the warming impacts of different greenhouse gases into a single measure, allowing for a comprehensive assessment of total greenhouse gas emissions.

Source: Our World in Data

Co2 Emissions

Carbon dioxide (CO2) emissions are the largest contributors to greenhouse gas GHG emissions, accounting for approximately 75% of the total. These emissions primarily result from activities such as burning coal, oil, and gas for energy production, manufacturing cement, and the consumption of solid, liquid, and gaseous fuels.

In terms of air transport, it is estimated that it contributes around 2% of global CO2eq emissions. Within the sector, approximately 81% of emissions come from passenger travel, while 19% originate from freight transportation.

Regarding passenger aviation, it is generally recognized that around 60% of emissions stem from international travel, while the remaining 40% come from domestic flights. However, it's important to note that specific percentages may vary depending on the data source and methodology used for estimation.

Source: Our World in Data

NON-CO2 EMISSIONS

Non-CO2 emissions encompass all emissions other than carbon dioxide. These emissions include gases such as nitrogen oxides (NOx), which contribute to the formation of ozone and have a warming effect on the atmosphere. Particulate matter (PM) is another type of non-CO2 emission that can impact air quality and human health.

In the context of aviation, non-CO2 emissions are a significant factor in the industry's environmental impact. These emissions are targeted for reduction through the implementation of cleaner technologies and the adoption of alternative fuels.

By addressing non-CO2 emissions, the aviation sector aims to mitigate its overall environmental footprint and promote more sustainable practices.

SCOPE 1, 2 AND 3 EMISSIONS

Scope 1 emissions: Direct greenhouse gas emissions from sources that are owned or controlled by an organisation.

For airlines, this includes emissions from fuel combustion on the ground and in flight, as well as emissions from other operations, such as maintenance and ground handling. Monitoring and reducing Scope 1 emissions is a key strategy for addressing the environmental impact of aviation and promoting sustainability in the industry.

Scope 2 emissions: Indirect greenhouse gas emissions resulting from the consumption of purchased electricity, heat, or steam.

For airlines, Scope 2 emissions would include emissions from electricity or heat produced at airports, as well as emissions from electricity used for other operations such as office buildings or data centres.

Scope 3 emissions: Indirect emissions from sources outside an organisation's control, such as emissions from the production and transportation of purchased goods and services.

For airlines, Scope 3 emissions include emissions from the production and transportation of jet fuel, as well as emissions generated during the manufacturing and maintenance of aircraft and other equipment.

WHAT ABOUT CONTRAILS?

Contrails, also known as condensation trails, are the visible trails left behind by aircraft in the sky. They form when the hot exhaust gases emitted by aircraft engines mix with the cold air at high altitudes. This mixture causes the water vapour present in the exhaust gases to condense into visible ice crystals or water droplets, along with other particles. While contrails themselves are not greenhouse gas emissions, they have an impact on the climate. Contrails can persist in the atmosphere for varying lengths of time, sometimes expanding and forming cirrus-like clouds. These contrail-induced cirrus clouds have the potential to trap heat radiated from the Earth's surface, contributing to a warming effect in the atmosphere. This impact on the climate system is often referred to as "contrail-induced radiative forcing."

It is important to note that the overall contribution of contrails to climate change is still a subject of scientific research and ongoing study. Nonetheless, the potential impact of contrails on the climate is a recognized area of concern and is being investigated for better understanding and potential mitigation strategies.

UK-based company Satavia, founded by volcanologist and entrepreneur Adam Durant, is working on a solution to significantly reduce the impact of contrails.

Using a weather prediction model, Satavia identifies flights likely to produce contrails and modifies their flight paths, avoiding atmospheric areas prone to contrail formation. This strategy targets only a small proportion of flights (5-10%) that are responsible for most of the contrail climate impact.

The first commercial flight using Satavia's technology took off in October 2021 with UAE's Etihad, with further trials planned with Dutch operator KLM. Studies suggest that diverting just 1.7% of flights could reduce contrail climate damage by 59%. However, regulatory adjustments and industry-wide collaboration will be necessary to fully realise these strategies.

• Also listen to our podcast with former Group CEO of Etihad Tony Douglas.