Aviation and Climate Change

As some parts of the world begin to emerge from lockdown, flights within these reqions are starting again. Inter-regional flights may take longer to re-establish because Covid-19 has not spread around the world uniformly, and different nations have responded differently to the pandemic. Nevertheless, IATA currently foresee that it will take until 2024 for ATMs (and their emsisions) to return to pre-Coronovirus levels.

In the days before the skies became so eerily quiet and devoid of con-trails, aviation was coming in for criticism because of the emissions it is responsible for; so-called “flight-shaming” has become an emerging social issue.

The “flygskam” movement is making people consider less carbon-intense alternatives to aviation, such as rail transport. However, non-aviation alternatives are not always a preferred option – for example installing new railways is land-intensive and energy-intensive (just consider all the steel rails which have be to be made).

Let’s be under no illusion, aviation will be under increased scrutiny as and when things return to normal; climate change activism will not go away. However it, and humanity in general, need to make sure that the momentum for change is directed in the right way.

As engaged members of the Aviation Fuel community, let’s look at the whole issue of aviation emissions, and how they are being improved. To do this, it is essential to first understand aviation’s importance to the global economy and how difficult it would be to replace it.

Prior to Covid-19 (the effects of which cannot yet be quantified), the global market had become in excess of 4 billion passengers and 60 million tonnes of air cargo each year. The US domestic market (by country, the largest single market) amounted to 600 million passengers a year, with China a close second above 500 million. The 8.5 million annual commercial flights in Europe carried one billion passengers, provided 3.3% of direct employment and contributed 4.1% of GDP. That market was worth in excess of €820 billion p.a. The air cargo industry accounted for 35% of revenues for the entire cargo transport industry in FY2018, according to IATA. It transported more than 60 million tonnes of generally high-value freight in 2019 – worth $6.8 trillion (but only 0.5 percent of total volumes).

Whilst some would wish for it, given the benefits that aviation brings in a developed global economy, it simply is not possible to stop flying, or to improve emissions overnight. Such measures take time. Sustainable flight should be the goal, not asking, or in some cases intimidating passengers not to fly.

Emissions are a direct function of the amount of jet fuel consumed. Typical emissions from an aircraft include CO2, water vapour, nitrogen oxides, methane, hydrocarbons, soot and other particulate matter and sulphur oxides. CO2 is the emission most in the public eye, and it is true to say that the environmental impact of the other emissions is less well-understood. CO2 is directly related to the fuel efficiency of the aircraft – it is a constant that every kilogram of fuel burned produces 3.16 kg of CO2 emissions.

The facts of the matter are that the global aviation industry produces around 2% of all human-induced CO2 emissions (totalling 915 million tonnes) and is responsible for 13% of all transport CO2 emissions. This compares with 72% of transport emissions coming from road transport (with the balance coming from shipping, rail etc.).

Commercial flight results in CO2 emissions of approx. 107 grammes per passenger per km travelled. A typical car has CO2 emissions of 120 g/km, and based on an average occupancy of 1.55 passengers, this becomes 77.4 grammes per passenger per km travelled.

So passenger air travel compares relatively well with road transport in specific CO2 emissions per km.

Of course, air travel serves a very different purpose, and as we have already seen, road transport is responsible for many times the emissions that aviation is responsible for.

Yet, aviation seems to be a low hanging fruit for climate change activism, and whilst road transport of all types (commercial, personal, leisure etc.) does come in for criticism and is regulated to improve its emissions, little is being said about the efforts that aviation makes.

As long ago as 2008, aviation was the first sector to set global goals for CO2 emission reductions – acheived by fuel efficiency improvements, stabilising net CO2 emissions from 2020, reducing net CO2 emissions to half of 2005 levels by 2050.

The results so far show a reduction in average fuel burn of 24% from 2005 to 2017. Each new generation of aircraft has tended to be some 20% more fuel efficient than its predecessor – therefore whilst enjoying annual growth in passengers in the order of 5% in recent years, fuel consumption by the sector has shown increases in the order of only 3% over the same period.

If only for airline cost reasons, improving an aircraft’s fuel burn also reduces CO2 emissions. This is a simple concept to grasp, but it is not easy to achieve.

Airframes and engines have high development costs and consequently they have long lifecycles. This is because the technology is often cutting edge and certification (in order to prove that an aircraft or sub-system is safe to fly) takes a long time to achieve and is costly. It is not unusual for an airframe (e.g. the Boeing 747) to have a lifecycle of 40 years and whilst individual aircraft may not have service lives quite that long, only minor changes are possible within that time.

Engines are the same, and whilst development is always ongoing, the basic architecture of an engine family (e.g. the Rolls Royce RB211 and the Trent developed from it, the General Electric GE90 and the GE9x developed from it) cannot not change quickly.

Therefore improvements are incremental, and an improvement of 1 or 2% in fuel consumption for each iteration is significant.

Whilst the percentages are not large, the fuel savings can be – consider a typical Code C narrowbody aircraft used on short haul flights. As a very general rule of thumb, it might consume 10,000 tonnes of jet fuel in a year. Consequently a saving of 1% would save 100 tonnes of fuel or 316 tonnes of CO2 or US$ 75,000 to the airline.

With this in mind, there has been a lot of interest in electric propulsion for aircraft. Whilst electric flight will be part of a future mix, liquid fuel-powered aircraft will be with us for decades to come for one reason – the energy that liquid fuels contain per unit mass. It takes a certain amount of energy to move one object (an aircraft) from one location to another, whether the energy source is liquid fuel or a battery pack.

A flight from London to Hong Kong, for example, by Boeing 747 will consume approx. 150 tonnes of jet fuel (which contains approx. 1.78 million kWh of energy). Based upon the best-available technology (from EV cars), a battery storing this much energy would weigh about 8000 tonnes. Clearly this is impracticle, and battery energy density needs to improve more than 50-fold in order to be a substitute for jet fuel. From past evidence, it is pretty clear that science will reach this goal, but not for perhaps 2 decades. That is why electric aircraft are now being developed (and at thevery small end of the market some have even flown) – not because the technology is ready now, but so that the aircraft are ready when the propulsion technology is available. Of course, there are many other barriers which must be overcome, including energy supply chains (charging infrastructure shortcomings for EVs generally cause range-anxiety for motorists; the problem is more pronounced for aircraft) and development of electric aircraft certification norms (the Federal Aviation Administration (FAA) and its European counterpart, EASA, are already working with industry on this).


The important issue is that the stakeholders are doing something and are responding to the wishes of the general public – whilst at the same time working with available and developing technologies. Because no single solution is available to address and reduce emissions, Aviation has adopted a so-called four-pillar approach to dealing with emissions:

  1. market-based measures – policy tools designed to achieve environmental goals at a lower cost and in a more flexible manner than traditional regulatory measures (essentially incentivising emitters through instruments for trade or offset of emissions);
  2. technology improvements – new engine technology, airline fleet replacement by more fuel-efficient aircraft;
  3. infrastructure and operations improvement – a variety of measures including engine-out taxiing, more efficient air traffic control, increased provision of fixed ground power at airports to reduce the use of aircraft GPUs (Ground Power Units) while on the ground (and focussing away from aircraft themselves as sources of emissions and looking at the whole Aviation sector – use of EVs at airports, implementation of green airports etc.)
  4. Sustainable Aviation Fuel

All these measures together are seen as the most responsible and practical way to move forward, with individual parts of the sector able to focus on those measures which best fit them.

In 2016, the 39th ICAO (International Civil Aviation Organization) Assembly adopted the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) to address CO2 emissions from international aviation.

CORSIA is complementary to the four pillar approach to help achieve ICAO’s goal of carbon-neutral growth from 2020 onwards. It relies on the use of emissions units from the carbon market to offset the amount of CO2 emissions that cannot be reduced through the use of technological and operational improvements, and sustainable aviation fuels.

It is the first sector-specific global offsetting mechanism which will address any annual increase in CO2 emissions of the industry above 2020 levels. CORSIA compares the total CO2 emissions for any year from 2021 onwards against a baseline level for 2019 and 2020. Whilst the effect of Covid-19 on skewing the 2020 air traffic figures has yet to be taken into account, by 2035 it was expected that CORSIA would mitigate approx. 2.5 billion tonnes of CO2 and raise c. $40bn of climate financing.

Nevertheless, it is the fuel itself which is responsible for most of the CO2 emissions associated with Aviation, and as we have seen, there is little alternative to the use of kerosene-type jet fuel either now, or in the near future:

  • the world needs to keep flying;
  • low-carbon and even zero-emission flights are a long way off and require considerable advances in technology;

A more immediately-available technology is Sustainable Aviation Fuel (SAF). In fact, there are many different types of SAF (they are a relatively well-established technology) – manufactured from different raw materials using different processes. SAFs are a range of hydrocarbon fuels synthesised from living matter (biomass, algae), CO2 and hydrogen which can then in theory be used as a conventional jet fuel substitute – or under current requirements, be blended with conventional jet fuel.

We have already stated that the pace of change in Aviation is slow because of the capital cost of development and due to flight safety, the necessarily conservative nature of approval and certifcation. In the case of SAF, this has meant that fuels will have to appear like, perform like, and use many of the same supply chains as conventional jet fuel. The concept is “drop-in”, whereby a SAF can be introduced into a jet fuel stream and continue through the supply chain to the end user, without any noticeable change in the fuel.

So far, this has been fine in principle. However, many questions remain unanswered at the moment. When compared with conventional jet fuel, some of them are:

  • who will cover the considerable cost disadvantage of SAF and cover the risk to capital that situations like Covid-19 have highlighted (passengers, taxpayers) ?
  • how clear is the environmental benefit – for example, how much energy is required to grow feedstocks and transport them to the place of SAF manufacture ?
  • how will production be scaled-up from laboratory to 24/7/365 worldwide availability ?
  • what will demand be when conventional jet fuel is the readily-available no barrier substitute ?

A lot of R&D effort is going into the sector. So far a few SAF technologies have been approved, but even fewer are in regular commercial use – in fact just one type.

Now that the first hurdle of how to certify SAF in line with international specifications for jet fuel have been overcome, there remain other hurdles – and opportunities.

The key one must be whether the industry will recover from Covid-19 to the extent that emissions reach anywhere near 2019 levels, and therefore cost aside, whether there is a role for SAF or whether emissions are on a sufficiently downward trend for them to be irrelevant.

We here at eJet strongly believe that continued downward progress on emissions can only be achieved by more efficient use of aviation fuel in general, use of aviation fuel with increasing sustainable content, and measures which make air travel less of a low-cost default.

In our next blog post we will go into SAF in more detail, and try to share our passion for it.




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