Aviation’s carbon footprint

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Air transport generated 895 million tons of carbon dioxide (CO2) in 2018. This may sound like a lot, but it is only around 2% of the 42 billion tons of CO2 generated by human activities every year.

If we consider energy-related CO2 emissions – without emissions from agriculture or forestry which account for around a quarter of global greenhouse gases – the largest contributor to CO2 emissions is electricity (44%). Second is road transport at 17%, followed by buildings at 10%.  

Due to the dramatic decrease in number of flights during the pandemic, the emissions dwindled substantially; the situation in aviation now is going back to the 2019 levels, which dredges up an old problem in the industry’s climate goals, while passenger numbers grow 5% every year, the industry becomes about 3% more efficient in reducing emissions.  

Between 91.5% and 92.5% of aircraft engine exhaust is normal atmospheric oxygen and nitrogen. Of the remaining, 7% to 8% is CO2 and water vapor and around 0.03% is nitrogen oxides, unburned hydrocarbons, carbon monoxide and Sulphur oxides, traces of hydroxyl family and nitrogen compounds and small amounts of soot particles (though modern jets have almost eliminated soot).

The reason that the environmental effects of aviation is often bolded is the height at which the emissions are released. The most significant greenhouse gas, CO2, does not have any additional impact due to difference in altitude, the impact is the same. However, other emissions such as nitrogen oxide and water vapor can have greater effect at higher altitudes, a phenomenon referred to as a ‘multiplier’. 

The water vapor trails (contrails) created by aircraft also have an impact; researchers believe that under certain circumstances, these vapors create ‘cirrus’ clouds, but the work on the impact of these clouds are yet inconclusive. For example, some research suggests these clouds may have different cooling and warming effects, depending on whether flights are during the day or night, so the results of further study on this occurrence could identify potential benefits.

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