Climate change and flying: what share of global CO2 emissions come from aviation?

The Controversial Role of Flying in Climate Change

In the ongoing discourse about climate change, few topics spark as much controversy as aviation. It's a paradoxical player in the climate narrative, contributing approximately 2.5% of global CO₂ emissions. However, when we account for the non-CO₂ impacts on climate, this figure rises to 3.5%. This complexity makes aviation a focal point in climate debates, and there are several reasons behind this contention.

Discrepancy Between Individual and Global Impact

One of the primary sources of debate surrounding aviation is the dissonance between its significance in individual carbon footprints and its global contribution. For frequent flyers, air travel stands as the dominant contributor to their personal carbon emissions. Yet, when viewed collectively, aviation constitutes a mere 2.5% of global carbon dioxide (CO₂) emissions. This disparity arises from significant inequalities in air travel, with many people unable to afford or access flights.

Attribution of Aviation Emissions to Countries

Adding to the complexity, emissions from domestic flights are included in a country's emission accounts, while international flights are categorized separately as 'bunker fuels.' This separation means that international aviation emissions don't count toward any specific country's emissions inventory, which in turn diminishes incentives for countries to reduce them.

Non-CO₂ Forcings Often Overlooked

Unlike more common greenhouse gases like carbon dioxide, methane, or nitrous oxide, the Paris Agreement does not include non-CO₂ forcings from aviation. This oversight is significant, especially considering that international aviation emissions are not factored into any country's emissions inventories or targets.

Quantifying Aviation's Impact

To grasp the role of aviation in global emissions and climate change, it's crucial to examine key statistics:

• Global aviation, including domestic and international travel, contributes to 1.9% of greenhouse gas emissions (encompassing all greenhouse gases, not just CO₂).
• 2.5% of global CO₂ emissions** can be attributed to aviation.
• 3.5% of 'effective radiative forcing'**, a closer measure of its impact on warming, is the share that aviation holds.

While these numbers may appear modest, they signify a significant challenge in climate mitigation. Most attention focuses on aviation's CO₂ emissions, primarily originating from the burning of jet gasoline.

Evolving Emissions

Historical data reveals that aviation emissions have doubled since the mid-1980s. However, these emissions have grown at a rate commensurate with total CO₂ emissions, resulting in aviation's share of global emissions remaining relatively stable, fluctuating between 2% to 2.5%.

Non-CO₂ Impacts Amplify Aviation's Role

Although aviation contributes 2.5% of global CO₂ emissions, its overall climate impact extends beyond this figure. Air travel emits a spectrum of gases and pollutants, influencing the climate in multifaceted ways. These emissions lead to a net warming effect, with some processes inducing short-term warming while others create cooling effects. When researchers factor in these complexities, aviation accounts for approximately 3.5% of effective radiative forcing, meaning 3.5% of warming.

Looking Beyond CO₂

Surprisingly, CO₂, while dominant in discussions, accounts for less than half of aviation's warming impact. Two-thirds (66%) arise from non-CO₂ forcings, with contrails, and the water vapour trails from aircraft exhausts, taking the largest share.

The Challenge of Decarbonizing Aviation

Aviation's contribution to climate change, though significant, remains smaller than many presume. Yet, it poses a unique challenge in terms of decarbonization. Unlike other major emitters, proven solutions to reduce aviation emissions remain elusive. While innovative concepts, such as hydrogen fuel cells and electric planes, are emerging, they are still on the horizon and face substantial technological and practical limitations.

As we grapple with aviation's role in climate change, the quest for sustainable solutions continues, guided by the urgent need to reconcile our love for flying with our responsibility to protect the planet.

Appendix: The Soaring Efficiency of Air Travel

As we explore the evolution of global emissions from aviation, it becomes evident that air travel has experienced substantial growth over the past half-century. What's intriguing, however, is that while aviation emissions have indeed risen, the surge in air travel volume has outpaced them significantly.

Emission Growth vs. Air Traffic Expansion

Since 1960, aviation emissions have soared nearly seven-fold, and since 1970, they have tripled. However, when we shift our focus to air traffic volume, represented by revenue passenger kilometres (RPK) travelled, the numbers tell a different story. Air travel has expanded by orders of magnitude more than emissions, with a nearly 300-fold increase since 1950 and a 75-fold rise since 1960.

The Triumph of Aviation Efficiency

This stark contrast between emission growth and air traffic expansion underscores the remarkable improvements in aviation efficiency. To illustrate this progress, we examine both the increase in global airline traffic since 1950 and aviation efficiency, measured as the quantity of CO2 emitted per revenue passenger kilometre travelled (RPK). In 2018, approximately 125 grams of CO2 were emitted per RPK. To put this into perspective, in 1960, this figure was eleven times higher, and in 1950, it was twenty times higher. Over the past five decades, aviation has witnessed a staggering surge in efficiency.

Multiple Sources of Efficiency

These efficiency gains can be attributed to various factors:

1. Aircraft Design and Technology:** Continuous advancements in aircraft design and technology have significantly enhanced fuel efficiency and reduced emissions.

2. Larger Aircraft Sizes:** The introduction of larger aircraft, capable of accommodating more passengers per flight, has contributed to lower emissions per passenger.

3. Increased Passenger Load Factor:** An essential metric, the 'passenger load factor,' measures the actual number of kilometres travelled by paying customers (RPK) as a percentage of the available seat kilometres (ASK) – the distance covered if every plane operated at full capacity. The global passenger load factor has surged from 61% in 1950 to 82% in 2018. This metric reflects the growing utilization of available flight capacity.

In summary, the aviation industry's remarkable efficiency improvements over the past five decades are evident in the ever-widening gap between the growth in air travel volume and the growth in emissions. These advancements signify the industry's dedication to reducing its environmental footprint and optimizing its operations, marking a significant step toward a more sustainable future for air travel.