Aviation's contribution to climate change is expected to intensify

A recent study emphasizes the critical need for concerted efforts and commitments to address the aviation sector’s impact on climate change. 

Non-CO2 emissions 

The comprehensive research underscores the complex nature of aviation’s environmental impact, particularly focusing on non-CO2 emissions like nitrogen oxides, soot, and water vapor. 

These emissions contribute significantly to global warming. For example, soot plays a role in the formation of contrails and “contrail cirrus,” line-shaped clouds generated by aircraft exhaust that increase high clouds, further warming the Earth’s atmosphere.

In-depth assessment 

The study was a collaborative effort by Manchester Metropolitan University, the University of Oxford, the University of Reading, and Imperial College London. 

The experts provide an in-depth assessment of aviation’s non-CO2 effects on both climate and air quality, considering current and future technological and fuel changes.

Inherent uncertainties 

“What we highlight is the inherent uncertainties that remain in some of these very complex effects on climate from non-CO2 emissions,” said Professor David Lee.

“More importantly, reducing the impact of emissions on the climate is not straightforward as practically all routes forward with conventional liquid hydrocarbon fuels involve ‘trade-offs’, mostly at the expense of emitting more CO2, whether it be technological or operational efforts.”

“These trade-offs and uncertainties mean that there are no simple silver bullets or low-hanging fruit to solve the problem. What is often forgotten is, that while the non-CO2 climate impacts of, for example, an individual flight are short lived, a substantial proportion of the emitted CO2 persists for a very long time, literally tens of millennia. This means it is a difficult balancing act if reducing non-CO2 emissions leads to an increase in CO2 emissions.”

Aviation impacts

Professor Keith Shine cautions against hastily adopting strategies to decrease non-CO2 climate effects that could inadvertently increase CO2 emissions. 

“We must be mindful that aviation affects local air quality as well as climate. Sometimes measures that improve one will be to the detriment of the other,” said Professor Shine.

The researchers noted that aviation accounts for about 2.5% of global CO2 emissions from human activities and approximately 3.5% of the change in the atmosphere’s energy balance. It also contributes around 4% of the increase in global mean temperatures. 

Complex challenge 

Decarbonizing the aviation sector is challenging due to its reliance on fossil kerosene (jet fuel) and the lengthy process of developing and replacing aircraft.

The pressing issue of aviation’s contribution to climate change is expected to intensify, especially with the sector’s growth after the COVID-19 pandemic. This contrasts with the emission reduction efforts in other sectors.

Future research 

Recognizing this challenge, the UK government, through the Natural Environment Research Council (NERC), has announced a £10 million research program to inform policy decisions in this domain. 

“This is a very welcome and much needed development by the government. Some of our previous research that was used by the Intergovernmental Panel on Climate Change (IPCC) has vitally informed the government on the scale of the problem,” said Professor Lee.

“We have endeavored to keep the Department for Transport informed of our work while we prepared this assessment, to inform the shape of future research needed.”

The study is published in the journal Environmental Science Atmospheres.

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