‘Offsetting’ is not the answer

Could aviation go green?


Boris Johnson defended his usage of short-haul air travel during the election campaign by claiming he was ‘offsetting’ the carbon dioxide (CO2) emissions associated with the flights.

But the public needs to be made aware of the bigger picture of plane travel and where offsetting stands in relation to greening aviation.

Global demand for air travel has increased considerably every year. Offsetting is one way in which individuals attempt to neutralise the impacts of their flying habits, but offsetting is not going to miraculously make flying environmentally green.

Market accountancy

Offsetting is a controversial short-term measure, and unfortunately, it is the only option available to the flying public.

But, it does no not ‘neutralise’ CO2 emissions as is often claimed by the third parties who sell offsets. Rather it shifts the problem elsewhere with very poor accountability and efficacy. 

It is a market accountancy measure rather than a real CO2 emission reduction measure. 

If we are going to seriously consider whether or not the aviation industry can go green, then I’d say new fuels could be the answer – but I do not believe the industry is moving fast enough. 

The aviation industry needs to take this matter a lot more seriously and they need to be demanding that governments take policy measures that force the whole system to produce zero-carbon fuel – because that is the only way out. 


At the moment, global aviation is accountable for 2.4 percent of global CO2 emissions. If ‘aviation’ were a country it would be in the top ten of global emitters. 

We categorise aviation in two different ways, domestic and international, with international aviation accounting for around 65 percent of global aviation emissions. 

Why are we struggling to improve these figures? One of the biggest challenges we face is growth. Aviation has been increasing over the long term at around 5 percent per year in terms of revenue passenger kilometres (RPK) – the number of kilometres travelled by paying passengers – and this has increased in the last decade to around 7 percent growth per year in RPK. 

On the other side of this, global fuel improvements are only around 1-2 percent per year – so are entirely drowned out by the sheer increase in RPK. So, despite small improvements to engine efficiency, improvements to fuel and the fact that fleets generally have a very slow turnover, emissions continue to increase. 

That said, when it comes to improving an aircraft’s fuel efficiency, a lot has actually been done over the years. But, I feel this improvement is starting to flatten out in favour of ‘easy wins’ within the industry. 


For example, aircrafts are generally very efficient things and loading them more economically – meaning as full as possible – improves that overall efficiency.

However, the issue of ‘tankering’, which was mentioned on the Panorama programme and is an issue which has been known about now for some time, is not helping. 

Tankering is when an aircraft is filled with extra fuel – more than the amount actually needed for a journey – just to avoid paying higher fuel prices at destination airports. This practice is having massive impacts on general overall emissions. 

The Paris Agreement (PA) states CO2 emissions from all sources must go to ‘net zero’ by 2050. 

In theory, domestic flights are included as part of the Nationally Determined Contributions (NDCs) within the agreement. NDCs are agreed emissions to be cut – however, international aviation is not mentioned at all. 

Emissions standards

This leads us to debate as to whether or not international aviation is even covered in the agreement. Really, anything that affects the global mean surface temperature of the earth should be included. 

This puts international aviation emissions – 1.6 percent of total annual CO2 emissions currently – on a direct collision course, unabated, with PA temperature lines. 

The international body that has ‘ownership’ of aviation emissions is the International Civil Aviation Organisation (ICAO), which is seemingly taking its own measures to tackle the aviation industry. 

It has recently set an emissions standard for CO2, a target that will not make a huge difference, and they have set up a global offsetting scheme to start in 2020. Again, this will not neutralise emissions as believed. 

On top of all this, aviation also has non-CO2 impacts, which also have adverse impacts on the environment. These mainly come from nitrogen oxides (NOx) emissions and contrails, which are the vapour trails we see behind an aircraft that spread into cirrus clouds. These too have a net warming effect and at least doubles the temperature effects from CO2 emissions alone. 

Carbon footprint 

Biofuels are one way of reducing the carbon footprint of the aviation industry, but they are highly variable depending on the fuel feedstock, and the land-use change of that associated crop. 

With the use of biofuels also comes issues over the area needed to plant the fuel source. Firstly, there is the argument of the importance of food versus fuel; then we must consider deforestation and biodiversity. 

Currently, aircrafts are certified to fly with biofuels as a mixture – usually 50/50 – but they are not available in quantity or as cheap as fossil-based kerosene. 

Perhaps the only solution would be to develop synthetic fuels from the ambient atmosphere (CO2 drawdown) and hydrogen (H2) generated from renewable energy sources? 

This solution is not available at scale or economically viable right now though. It would take a big brave policy to make this happen, such as banning aviation fossil fuel-based kerosene and setting a date to enforce this, as well as big industrial investment into research and development. 

Fuel prices

This might also have a knock-on impact on aviation fuel prices, affecting demand. 

Why would this be such an attractive solution? Synthetic fuels are low in or have zero aromatic content. Aromatic content refers to the formation of ‘soot’, which comes from the exhaust of an aircraft that is fuelled using kerosene.

These tiny soot particles are both damaging to health and trigger the formation of contrails and contrail cirrus clouds, which have a non-CO2 warming effect. 

Such a fuel would be a win-win, lower CO2 emissions, no contrails and better for both the environment and health. 


So in conclusion, to me, neither ‘efficiency’ or ‘offsetting’ provide a sufficient solution. 

I believe if people Like Mr Johnson really want to avoid being ‘flygskam’, or ‘flightshamed’, then policy actions are desperately needed, as is considerable investment into the production of synthetic fuels from renewable sources and energy. 

This Author

Professor David Lee is director of the Centre for Aviation, Transport and the Environment at Manchester Metropolitan University.