Kieran Tait – Cabot Institute for the Environment blog

Why the aviation industry must look beyond carbon to get serious about climate change

Posted on September 5, 2022March 29, 2023 by janet.crompton

Flying is responsible for around 5% of human-induced climate change.
Wichudapa/Shutterstock

Commercial aviation has become a cornerstone of our economy and society. It allows us to rapidly transport goods and people across the globe, facilitates over a third of all global trade by value, and supports 87.7 million jobs worldwide. However, the 80-tonne flying machines we see hurtling through our skies at near supersonic speeds also carry some serious environmental baggage.

My team’s recent review paper highlights some promising solutions the aviation industry could put in place now to reduce the harm flying does to our planet. Simply changing the routes we fly could hold the key to drastic reductions in climate impact.

Modern aeroplanes burn kerosene to generate the forward propulsion needed to overcome drag and produce lift. Kerosene is a fossil fuel with excellent energy density, providing lots of energy per kilogram burnt. But when it is burnt, harmful chemicals are released: mainly carbon dioxide (CO₂), nitrogen oxides (NOₓ), water vapour and particulate matter (tiny particles of soot, dirt and liquids).

Aviation is widely known for its carbon footprint, with the industry contributing 2.5% to the global CO₂ burden. While some may argue that this pales in comparison with other sectors, carbon is only responsible for a third of aviation’s full climate impact. Non-CO₂ emissions (mainly NOₓ and ice trails made from aircraft water vapour) make up the remaining two-thirds.

Taking all aircraft emissions into account, flying is responsible for around 5% of human-induced climate change. Given that 89% of the population has never flown, passenger demand is doubling every 20 years, and other sectors are decarbonising much faster, this number is predicted to skyrocket.

Aircraft contrails don’t last long but have a huge impact.
Daniel Ciucci/Unsplash

It’s not just carbon

Aircraft spend most of their time flying at cruise altitude (33,000 to 42,000 ft) where the air is thin, to minimise drag.

At these altitudes, aircraft NOₓ reacts with chemicals in the atmosphere to produce ozone and destroy methane, two very potent greenhouse gases. This aviation-induced ozone is not to be confused with the natural ozone layer, which occurs much higher up and protects the Earth from harmful UV rays. Unfortunately, aircraft NOₓ emissions cause more warming due to ozone production than they do cooling due to methane reduction. This leads to a net warming effect that makes up 16% of aviation’s total climate impact.

Also, when temperatures dip below -40℃ and the air is humid, aircraft water vapour condenses on particles in the exhaust and freezes. This forms an ice cloud known as a contrail. Contrails may be made of ice, but they warm the climate as they trap heat emitted from the Earth’s surface. Despite only lasting a few hours, contrails are responsible for 51% of the aviation industry’s climate warming. This means they warm the planet more than all aircraft carbon emissions that have accumulated since the dawn of powered flight.

Unlike carbon, non-CO₂ emissions cause warming through interactions with the surrounding air. Their climate impact changes depending on atmospheric conditions at the time and location of release.

Cutting non-CO₂ climate impact

Two of the most promising short-term options are climate-optimal routing and formation flight.

Left: Climate optimal routing. Right: Formation flight concept.

Climate-optimal routing involves re-routing aircraft to avoid regions of the atmosphere that are particularly climate-sensitive – for example, where particularly humid air causes long-lived and damaging contrails to form. Research shows that for a small increase in flight distance (usually no more than 1-2% of the journey), the net climate impact of a flight can be reduced by around 20%.

Flight operators can also reduce the impact of their aircraft by flying in formation, with one aircraft flying 1-2 km behind the other. The follower aircraft “surfs” the lead aircraft’s wake, leading to a 5% reduction in both CO₂ and other harmful emissions.

But flying in formation can reduce non-CO₂ warming too. When aircraft exhaust plumes overlap, the emissions within them accumulate. When NOₓ reaches a certain concentration, the rate of ozone production decreases and the warming effect slows.

And when contrails form, they grow by absorbing the surrounding water vapour. In formation flight, the aircraft’s contrails compete for water vapour, making them smaller. Summing all three reductions, formation flight could slash climate impact by up to 24%.

Decarbonising aviation will take time

The aviation industry has fixated on tackling carbon emissions. However, current plans for the industry to reach net zero by 2050 rely on an ambitious 3,000-4,000 times increase in sustainable aviation fuel (SAF) production, problematic carbon offsetting schemes, and the introduction of hydrogen- and electric-powered aircraft. All of these could take several decades to make a difference, so it’s crucial the industry cuts its environmental footprint in the meantime.

Climate-optimal routing and formation flight are two key examples of how we could make change happen faster, compared with a purely carbon-focused approach. But there is currently no political or financial incentive to change tack. It is time governments and the aviation industry start listening to the science, and take aircraft non-CO₂ emissions seriously.

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This blog is written by Cabot Institute for the Environment member Kieran Tait, PhD Candidate in Aerospace Engineering, University of Bristol. This article is republished from The Conversation under a Creative Commons license. Read the original article.

Kieran Tait

An insight into aviation emissions and their impact on the atmosphere

Posted on November 19, 2019April 13, 2023 by janet.crompton

Image credit: El Ronzo, Flickr

The proliferation of aviation has brought about huge benefits to our society, enhancing global economic prosperity and allowing humanity to travel faster, further and more frequently than ever before. However, the relentless expansion of the industry is a major detriment to the environment on a local, regional and global level. This is due to the vast amounts of pollution produced from the jet fuel combustion process, that is required to propel aircraft through the air and to sustain steady level flight.

Aircraft impact the climate largely through the release of CO2, which results in a direct contribution to the greenhouse effect, absorbing terrestrial radiation and trapping heat within the atmosphere, leading to rising temperatures. However, it is also vital not to overlook the non-CO2 aircraft emissions such as NOx, soot and water vapour, which result in alternative climate change mechanisms – the indirect greenhouse effect, the direct aerosol effect and aviation induced cloudiness. When accounting for these non-CO2 effects, it can be assumed that the climate impact is doubled or tripled compared to that of CO2 alone.

This report provides the necessary background information to grasp the science behind aircraft emissions and delves into the impacts aviation has on the atmosphere’s ability to cleanse itself of harmful emissions, otherwise known as the oxidising capacity of the atmosphere. It does so through an analysis of three distinct and commonly flown flight routes, investigating the impact that each flight’s emissions have on the surrounding atmospheric chemistry and discusses the potential effects this has on our Earth-atmosphere system.

Read the full report by Kieran Tait

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Tackling the climate crisis with energy transitions

Posted on September 30, 2019March 31, 2023 by janet.crompton

Aerospace Engineering student Kieran Tait recently returned from a transformative journey through Western Canada, representing the University at the Energy Transitions summer school at the University of Alberta. A timely topic following the recent declaration of climate emergency here at the university.

Kieran underneath a glacier in Lake Louise, Banff National Park.

Throughout the two weeks, we endured a 40-hour lecture series, in which world-leading industry experts and researchers presented to us the current state of energy, the outlook for the future and an insight into different types of energy systems and their relative merits. This was superbly rounded off with insightful field trips including a tour around a wind farm and a hydroelectric dam, which really helped to contextualise the lectures.

The course was coordinated by the Worldwide Universities network, in which 21 representatives from 13 universities worldwide came together to study the practicalities of decarbonising society. The network brought a diversity of cultures and study areas together, which really shed light on the interconnectedness of the energy crisis and the need for mass mobilisation of society to focus minds on the solutions to the single biggest existential crisis humanity has ever faced. Climate breakdown.

The impending breakdown of our climate is an issue faced by every living being on Earth: no matter your nationality, race, gender, beliefs or background, the impacts of a warming world will completely transform your standard of living in the coming decades unless drastic steps are taken in the next 18 months to transition away from our current overconsuming, unsustainable way of life.

If we fail to meet this objective, we can expect unprecedented weather events, resulting in scarcity of basic human resources such as land, food and water, mass migration in the hundreds of millions and potentially the collapse of civilisation as we know it. Worse still, we can expect all of this as early as 2050 if action is not taken immediately. The seemingly impossible task imposed on our current generation is unparalleled in scale and complexity. It will require a collaboration among all disciplines and every nation on earth to achieve the sort of far reaching and functional solutions required to give us the best chance of limiting the warming trajectory preventing us from passing the point of no return.

Visiting the TransAlta wind farm in Pincher Creek, known as the Wind Capital of Canada.

The course in Energy Transitions provided me with the fundamental knowledge required to propose a logical working plan to phase out the current destructive energy policy and replace it with a more sustainable alternative. This included an overview of current climate science and projections for the future global energy mix, followed by an insight into a variety of energy production methods, including traditional fossil based systems such as coal, oil and gas and renewable types such as wind, solar, hydro, marine, geothermal, nuclear, biomass and hydrogen fuel cells.

The science behind each technology was explained thoroughly and the social, environmental and political implications associated with each type were also discussed. Also carbon sequestration methods such as Carbon Capture, Utilisation and Storage and land reclamation were explained to us in great depth, as it is clear that we need to not only reduce emissions to zero, but also begin to remove emissions that already exist in the atmosphere if we are to maximise our chances of staying below 1.5 degrees Celsius.

Alongside lectures, we also got the chance to go to Pincher Creek, a town in southern Alberta which is home to a large number of wind farm projects, making use of the region’s windy climate. We got the chance to visit a wind farm and go inside a turbine and we were also shown around a hydroelectric dam, bringing to life the concepts studied in lectures. Further to this we visited Waterton Lakes national park to experience some of the natural beauty Canada has to offer.

The group outside the house of the University’s founder Alexander Rutherford, before a ceremonial dinner.

When we returned, it was back to work as we all were tasked with presenting to the rest of the group, a proposal for energy transition solutions throughout different areas of the world. My team and I were given the job of proposing an EU wide energy transition plan. A timely subject following the newly appointed European Commissioner’s calls for a climate-neutral Europe by 2050. This task involved reviewing current policy and future goals, developing a sustainable infrastructure plan which would sufficiently meet increasing demand and discussing the issues associated with this transition.

Working with students from Spain, Ghana and Brazil led to some contrasting opinions and views on various subject matters, however the overwhelming consensus was that the transition had to phase out fossil fuels as soon as possible, acknowledging the need to sacrifice living standards in order to allow this rapid transition to happen. It is reassuring to know that despite our cultural differences, we all share the same view that action must be taken immediately, and we must undergo a process of degrowth to cut further emissions and keep temperature rises to a minimum to avert catastrophic climate change.

All in all, this course excelled at bringing like-minded inquisitive individuals together from a diversity of cultures and backgrounds to discuss the most pressing technological, political and ethical challenge humanity has ever faced. It’s admittedly a very frightening time to be a young person, but its undeniable that the times ahead present humanity with a chance to reach a new age in technological and cognitive ability and will allow for multi-national cooperation like the world has never seen before. I would like to thank the Worldwide Universities Network, the University of Alberta and everybody involved for making this incredible experience a possibility!

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This blog is written by University of Bristol engineering student Kieran Tait. It’s fantastic to hear Kieran’s passion and enthusiasm for combating the climate crisis we are facing through engineering and renewable energy solutions. This is something that the University is highly committed to and this year world-leading renewable energy expert Andrew Garrad will be joining the Faculty as a visiting professor to enhance our teaching of sustainable energy not only to our engineering undergraduates but to students across the University. This blog has been reposted with kind permission from Kieran and the Faculty of Engineering blog. View the original post.