Understanding Aviation's Climate Impact

Jonathan Preist

In this video, Jonathan Preist delves into the Working Group I assessment of the physical science basis. He covers the different greenhouse gases and the complex effects of aviation on climate, from Carbon Dioxide emissions to Contrails and Nitrogen Oxides.

Aviation sector

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Understanding Aviation's Climate Impact

9 mins 17 secs

Key learning objectives:

Understand the historical impact of aviation on climate and the different mechanisms contributing to aviation’s impact on the climate
Understand the notions of Short-term and Long-term Climate Forcers, the timescales and relative uncertainties associated with aviation’s contributors
Understand the need for a strong reduction in contrails impact in the next decades, in order to limit the temperature peak as per Paris Agreement

Overview:

Aviation, responsible for 3.8% of anthropogenic effective radiative forcing, which is a measure of the rate of change of energy accumulation on earth. reveals complexities involving CO2 emissions, contrails, and nitrogen oxides. This video sets the stage for mitigation discussions, emphasising the urgency to understand and address aviation's role in shaping our climate.

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Summary

What does Working Group 1 analyse in terms of climate science?

WG I analyses various aspects relating to physical science elements such as greenhouse gases, temperature changes, the hydrological cycle, extreme weather, glaciers, oceans, biogeochemistry, carbon cycle and climate sensitivity. This builds a complete picture of the climate system and how it is changing, including the attribution (or causes) of change. Confidence in findings is crucial, assessed based on evidence robustness and consistency.

The findings of WG I are the foundation for the adaptation and mitigation studies of the WG II and WG III.

What is the contribution of aviation to climate change?

In 2018, aviation contributed 2.5% of anthropogenic CO2 emissions since the pre-industrial era. More significantly, it accounted for 3.8% of anthropogenic effective radiative forcing (ERF), representing the Earth's energy imbalance, with implications for temperature change. However this figure is the result of a number of factors that are quite complex, requiring us to distinguish between CO2 and non-CO2 effects. This in turn requires a broader understanding of the difference between the IPCC list of greenhouse gases and aviation's non-CO2 effects.

What is the difference between aviation’s non-CO2 effects and the non-CO2 greenhouse gases?

The IPCC’s list of greenhouse gases includes:

CO2 (Carbon Dioxide)
CH4 (Methane)
N2O (Nitrous Oxide)
F-gases (CFCs, HFCs, PFCs, SF6)

However, aviation does not contribute significantly to anthropogenic emissions of any of these gases.

What are the non-CO2 effects of aviation?

Condensation trails (contrails) that can form and persist behind the engines in certain atmospheric conditions
Engines also produce nitrogen oxides or NOx. These are not greenhouse gases themselves however they influence the creation and destruction of greenhouse gases in the atmosphere.

What are condensation trails and what is their impact?

They are the line-shaped ice clouds formed by the condensation of the water vapour in the engine exhaust. During the day, when a cloud generates shade it reflects some energy from the sun back into space. During the night it traps some heat radiated by the earth towards space, increasing the local greenhouse effect. Of these two phenomena it is the latter that dominates, hence contrails have a net heating effect. The IPCC’s attribution studies indicate that in 2019, aviation’s contrails alone contributed 2.2% to anthropogenic ERF and were responsible for 1.6% of the historical anthropogenic temperature increase.

What are nitrogen oxides or NOx and what is their impact?

They are formed at high temperatures during combustion in the engines and they interact with trace gases in the troposphere and stratosphere and this impacts the concentrations of 2 other greenhouse gases:

They form ozone, with a warming effect
They destroy methane, with a cooling effect

However, the net effect is warming.

What is the IPCC summary on the contribution of aviation to climate change?

Contrails and NOx emissions induce strong, but short-lived warming contributions, while CO2 dominates the long-term warming impact.

Regarding the lifetime of forcers:

Short-lived climate forcers (SLCFs) have short atmospheric lifetimes relative to CO2, ranging from hours to about two decades. They can be direct (like methane), or indirect (like contrails and NOx emissions)
Long-lived climate forcers include CO2 and NOx and have longer atmospheric lifetimes.

The time dependence of the impact of the different emissions is important to be mindful of when comparing them. Also, the timescale over which the impact of a mitigation action can be observed, depends on the lifetime of the impacted climate forcer.

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Jonathan Preist

Jonathan Preist, a 20-year Airbus employee, has extensive experience in Overall Aircraft Design, which encompasses various aspects of aircraft performance and environmental impact. After completing a master's degree in Global Management of Corporate Social Responsibility and Sustainable Development at Mines ParisTech, Jonathan focuses on educating Airbus Commercial Aircraft engineers to have a transformative impact on the company and its products. He defines sustainability competences and designs training courses, video pathways, seminars, and infographics. Jonathan collaborates with French engineering schools Supaero, ENAC, INSA, and Campus de la Transition, aiming to equip engineering students and professionals with theoretical knowledge and practical skills.

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