Aviation is a relatively small contributor to climate change. However, with predicted industry growth, that amount is set to slowly rise.

CO2 emissions are the principal cause of global warming and the United Nation’s Intergovernmental Panel on Climate Change (IPCC), the foremost global authority on the issue, has confirmed that aviation contributes 2% of the world’s CO2 emissions.

This is small compared to the principal sources of CO2 emissions, such as power generation and road transport, but this does not mean that the aviation industry can ignore its contribution to combating climate change.

The IPCC forecasts that aviation’s CO2 emissions could rise to 3% of the global figure by 2050. Consequently, the air transport industry is undertaking many activities to reduce its contribution to climate change as much as possible, many of which you will find out about in this website.

Carbon dioxide, CO2, the most important greenhouse gas – has the same effect on the environment, whatever the source and wherever it is emitted.

However, aircraft engines, like cars, trucks, ships and trains, emit other gases too. Some of these may also affect the climate, and some may have a greater effect at altitude than at ground level. Soot is an example, but soot emissions from jet engines have been largely eliminated in the last 20 years.

Oxides of nitrogen (NOx) are another example, but they can have both warming and cooling effects. Water vapour in the form of contrails can lead to cloud formation, which is recognised as a challenge for the industry.

Essentially, CO2 effects are well known and understood, other emissions much less so. There is an additional effect at altitude, but it has not been adequately quantified. However, it is not of a magnitude that justifies diversion of attention away from the main focus, which is CO2.

Condensation trails or “contrails” are the visible trails of water vapour sometimes left by aircraft as they fly. Contrails may in turn trigger the formation cirrus clouds.

At present, no-one is entirely certain to what extent contrails and related clouds contribute to global warming. It is thought that contrails, by creating clouds, could trap outgoing radiation emitted by the Earth and atmosphere at a greater rate than they reflect incoming radiation from the sun. This could increase global warming.

However, the effect varies daily and annually, and the overall extent of warming is not well known. Furthermore, it has even been suggested that cirrus clouds can sometimes cause global “cooling” and potentially slow the effects of climate change. In fact, scientific understanding of how even naturally-formed clouds impact climate change is an area of great uncertainty. The aviation industry is able to avoid contrail formation, but at the expense of flying lower or around the conditions in which contrails are able to be formed. This would increase fuel use and therefore CO2. Clearly, a better understanding is needed before formulating appropriate responses.

When you fly you normally take the most direct route between two points, while when you drive or take the train the distance between the same two points is 30 to 40% longer.

However, aircraft are not always allowed to use the shortest distance, as they are often forced to ‘zigzag’ due to restrictions in airspace imposed by governments.

In Europe, for example, the airspace is patched together from old national systems, with segmentation into small, inefficient blocks which use a variety of different air traffic control technologies. The creation of a Single European Sky, on which the industry is working together with European regulators, will bring significant environmental benefits, through the reduction of holding (aircraft flying in a fixed pattern waiting for permission to land), more efficient routings thanks to the design of functional airspace blocks, and enhanced optimal flight profiles.

Shortening routes can indeed significantly reduce CO2 emissions. In fact, every minute of flying time knocked off a journey saves 62 litres of fuel and 160kg of CO2 emissions. And everyone arrives sooner! Therefore, all over the world, airlines and air navigation service providers are looking to shorten routes wherever possible. 

The industry is actively developing and testing potential alternative sources of fuels for aviation. When blending biofuel made of crops or algae with traditional jet fuel, it is possible to substantially reduce CO2 emissions. All fuels produced from alternative sources – or feedstocks – must achieve the same specification of standard aviation fuel – Jet A1. They can then be certified for ‘drop in’ use as they are no different to standard fuel.

However, industry continues to examine using alternative fuels in the future with major airlines pushing forward alternative fuel projects and trials.

Hydrogen is being explored for application in the very near future in fuel cells for the auxiliary power units (APUs) that provide energy to aircraft standing at the gate. Hydrogen might in the very long become an option for aircraft engines, although significant design and infrastructure changes would be required, in particular regarding the size of the tanks since hydrogen is lighter but far more voluminous than jet fuel.

Aircraft manufacturers are constantly redesigning and re-engineering aircraft, to incorporate advancements in technologies and designs. Manufacturers have developed lighter materials, more aerodynamic designs, and better engines so that the aircraft they produce are more efficient, reducing fuel burn and therefore emissions.

There are case studies on the new generation of aircraft that have just entered service, or are going to do so in the coming years:

Yes, aircraft engines are becoming more and more efficient and are helping limit the impact of aviation on climate change. Continuing to improve efficiency is a key consideration for aircraft engine manufacturers. New materials are being developed and used to seek every little opportunity for greater efficiency, whilst new designs are having a marked reduction in fuel consumption.

There are case studies from each of the engine manufacturers on the projects they have in place:

  • Rolls-Royce
  • CFM International
  • Pratt & Whitney
  • GE Aviation

Engine manufacturers are also cutting emissions of non-CO2 emissions such as oxides of nitrogen or NOx. For example, in the 1990s, the engine manufacturer CFM International pioneered the development of an ultra-low NOx combustor for aircraft, reducing NOx emissions by up to 40%.

Aviation transports people across the world, over distances of up to 15,000 km.

A high-speed train can be a suitable alternative or complement between large cities, while air transport remains the best, if not the only option for trips above 1,000 km, which represent 80% of air traffic.

Intermodal solutions combining high-speed trains and planes are being developed. This is the case, for example, between Charles de Gaulle Airport in Paris and Brussels Airport where Air France transports its passengers arriving from North America or Asia via high-speed train. This rail link replaces all flights between these two cities.

High-speed trains have a large capacity, which limits its usefulness to markets between large cities. For regional links between medium-sized cities, air transport is more efficient and cost-effective since it has the flexibility to adapt the aircraft-type to the size of the market (from fewer than 20 seats to a few hundred).

It is important to remember that trains do also produce emissions – directly through diesel engines and indirectly as they run off the electricity grid. Generally, their noise footprint is larger than aircraft and they also have a much greater land use footprint. In most parts of the world, train travel also requires very large government subsidy to operate.

Carbon offsetting is a voluntary way of combating climate change by funding sustainable projects all over the world.

Although it is perhaps not a long-term solution, offsetting means paying a little more for your ticket to compensate for the CO2 resulting from your flight. The money helps to fund diverse projects around the world; for example, to replace non-renewable fuel, such as coal, with renewable forms of energy such as biomass or solar, or perhaps to support forest restoration, which helps absorb CO2 from the atmosphere.

More and more airlines are offering passengers the opportunity to offset their carbon emissions, often as part of the booking process. The International Air Transport Association (IATA) has also developed an offsetting programme that airlines can use. On top of this many organisations are helping individuals and companies to offset their carbon emissions through specialist carbon offsetting websites.

There are many different techniques used by airports and airlines. In some countries, all waste coming off an aircraft must be destroyed for quarantine reasons and many of these airports are now moving from incinerating this waste to more environmentally-sound techniques such as steam sterilisation. However, the industry is working with government authorities to determine if recycling of international on board waste can start taking place. Many airlines do recycle domestic flight waste.

Recycling bins have been installed in the passenger terminal buildings of many airports and in their administrative facilities. Thus, waste is sorted before being collected in order to reduce the volume of refuse and to maximise recycling. Bottles, cans, sometimes newspapers, batteries and other recyclable items are recovered by designated collectors.

Another example of waste and recycling concerns ‘de-icing’. In cold climates, both aircraft and runways have to be de-iced to prevent any risk of accidents. Airports limit the impact of de-icing activities by collecting and reusing the de-icing chemicals. Traditional de-icing fluids are being replaced with products that are less polluting or even fully biodegradable.

There are a number of reasons why you might have to taxi to or from the runway for a long time in an arriving or departing aircraft at some airports. One reason is that the runway your flight will use may be located some distance from the terminal building (remember that runways are often three or four kilometres long).

However, the most common reason for lengthy taxiing is congestion on the ground. There will be different reasons for this, depending on the airport, but the industry has determined that congestion is a major contributor in some regions, and will continue to be as passenger numbers grow. Traffic delays affect the quantity of emissions released and also inconveniences passengers.

Expansion of airport facilities and more efficient use of air routes will help ease the congestion experienced at some airports.

The simple answer is because of capacity constraints at airports and in the air over major hubs – when there are large numbers of aircraft trying to use the same runway or airspace, air traffic control will queue the flights and allocate them slots to land in safely.

All sectors of the air transport industry are working together to reduce the amount of time that flights have to circle through more efficient landing approach techniques, flight paths and on-the-ground operational programmes to clear runways more quickly. However, at some of the more constrained airports such as London’s Heathrow, the only option may be to build more runway capacity.

As a result of political and public pressure, it may become increasingly difficult for airports in some regions to be allowed to increase capacity unless the aviation sector can demonstrate that it is addressing its impact on climate change and other environmental issues. Aviation partners understand that proactive work is vital to ensure the ability to meet the capacity challenge.

Of all the different forms of transport, cars produce by far the most CO2 emissions.

According to the Stern Review (The Economics of Climate Change), cars are responsible for 76% of all CO2 emissions from the transport sector with ships and aircraft 10% and 12% respectively.

The heavier an aircraft, the more fuel it consumes and a large portion of an aircraft’s weight is due to cargo and baggage carried. A plane saves 34,000 litres of fuel per year for each kilogramme less in weight per seat.

Each individual traveller can, therefore, make a big difference to fuel consumption by packing lightly. The cumulative weight reduction will reduce the total loaded weight of the aircraft and enhance fuel economy, which, in turn, means fewer CO2 emissions.

Packing tips can be found in many places online. For example, see these packing tips from the American Society of Travel Agents (ASTA).

More generally, you might also wish to look at the travel tips on responsibletravel.com.

There are other ways to limit your climate change impact when flying. How you decide to travel to the airport can affect CO2 emissions and local air quality. For example, choosing public transport rather than taking a car saves emissions.

More and more passengers are also choosing to offset the emissions of their flight. Please see the answer to the question 'How does carbon offsetting work?' for more information on offsetting your flight.

An emissions trading scheme is a way of reducing CO2 emissions by setting an overall limit on emissions, then allowing companies to buy and sell emission ‘allowances’ to meet their reduction targets.

Each company participating in the scheme is allocated a certain level of free CO2 credits. For example, a particular company might receive credits for 100,000 tonnes of CO2 a year. If it produces less than this amount, it can sell its surplus allowances to other companies who cannot compensate for their emissions using their free allocation. Because emissions allowances have cash value, those companies that are able to reduce emissions below their targets can make money by selling credits, whereas those that exceed their targets have to buy credits. The intent of such a scheme is to incentivise reductions in industries that can achieve reductions most cost-effectively.

Emissions trading schemes are either mandatory or voluntary. Mandatory schemes can be found in the USA, where emissions trading is used to reduce sulphur dioxide from electric utilities, and in the European Union (EU) where an emissions trading scheme aims to reduce CO2 emissions from industrial installations.

In December 2006, the European Commission (EC) proposed to expand its current emissions trading scheme to cover CO2 emissions from the aviation industry. All flights to and from the EU would be included from 2012. This placed a cap on CO2 emissions from flights, while allowing airlines to grow by purchasing allowances from other industries as well as from a number of emissions reducing projects in the developing world. Since the scheme sets an overall limit on emissions, the overall environmental benefit is guaranteed. Whilst airline associations such as IATA initially welcomed the EU ETS as an appropriate tool, when the scheme was expanded to include international aviation, the airlines signalled the political difficulties with the system.

However, due to significant opposition from countries outside the EU and in order to help smooth the way for negotiations on developing a global market-based measure at the International Civil Aviation (ICAO), the EU paused the implementation of its scheme for international flights in 2012. The industry stands united behind the need to address emissions from international aviation at a global level, through ICAO.

You can find more information about emissions trading from the economic measures section of this site, the International Air Transport Association (IATA) and the Association of European Airlines (AEA).

The amount of CO2 that a company can emit under an emissions trading scheme can be allocated in different ways. Simply put, allowances are distributed to companies either by ‘auctioning’ or by distributing them free-of-charge. When distributed free-of-charge, allowances can be determined by past emissions of the company (‘grandfathering’) or by basing the allocation on their emissions’ efficiency when compared with a sector average (‘benchmarking’).

With regards to aviation, the auctioning of allowances could have a very substantial cost impact, as competing airlines will drive up the price. Allowance distribution based on past emissions (grandfathering) would penalise airlines that took early action to modernise their fleets and reduce CO2, while a benchmarking approach, if designed properly, would reward more efficient operations. A benchmarking approach may however privilege certain business models over others, creating market distortions.

The aviation industry believes that climate change is a global issue that requires a global solution through the International Civil Aviation Organization (ICAO) – the UN body dealing with aviation at the worldwide level. This is the best way to minimise competitive distortions and to maximise environmental benefit.

A well-designed market-based measure should be based on the consent of those states whose airlines are involved in the scheme, on the understanding that the unilateral inclusion of foreign airlines or flights to and from states outside the scheme should be avoided.

Airlines believe a market-based measure is a useful tool to manage the industry’s greenhouse gas emissions, while strongly opposing fuel taxes and emission charges that do nothing for the environment.

Emissions trading or other MBMs should only be considered as a complement to other more efficient and permanent measures such as technological, operational and infrastructure developments, which can deliver direct environmental benefits.

No. If anything, green taxes harm the industry’s ability to limit its climate change contribution.

This is due to a number of reasons. Taxes drain the aviation sector of financial resources needed for investments into research and development.

Green taxes are explicitly aimed at changing demand for air transport – which simply means pricing passengers out of the market. This is made worse by the fact that, in many instances, travellers have no reasonable alternative to air transport.

Green taxes on aviation deliver additional revenue for governments with no guarantee that this revenue will be used for environmental objectives, neither for the passenger nor the airline. They provide no incentive whatsoever for airlines to invest in more efficient aircraft, or more efficient fuels: both major factors in reducing CO2 emissions that should be encouraged not discouraged.

Green taxes are not a viable solution to address aviation’s contribution to climate change.

We do not need to fly less, but we do need to adopt a responsible approach to limiting aviation’s impact and that is exactly what the commercial aviation industry is doing.

Flying meets the need for global connections, and without it the global economy would suffer. In many cases, flying simply cannot be replaced by other modes of transport. In many parts of the world, road and rail infrastructure is grossly inadequate. Traffic demand is growing worldwide, not diminishing, including developing nations that are in great need of affordable passenger and cargo traffic to build their economies.

The right choice is not to fly less, but to continue to make sure that the air transport sector proactively and progressively addresses emissions, noise, and a range of community concerns in order to balance environmental commitment and growing capacity needs.

International air services are exempt from fuel taxes under the Chicago Convention. The Chicago Convention establishes the rules of airspace, aircraft registration and safety, and details the rights and obligations of countries around the world in relation to international air travel.

Fuel tax exemption is not an ‘unfair subsidy’ for aviation. The Chicago Convention is based on the international legal principle of ‘reciprocity’ where States agree to mutual tax exemption in order to avoid unilateral imposition of fiscal measures. However, this does not restrict States from imposing fuel taxes on domestic air services, which some do, or indeed other taxes on the ticket, passenger, customs, immigration, etc. – taxes which are quite universal.

Generally speaking, it is a falsehood to say that aviation is ‘under taxed’. In fact, the opposite is true: in many places aviation is as heavily taxed as alcohol and tobacco. Far from enjoying tax privileges, air transport finances its entire infrastructure costs through specific user charges such as landing, en-route and passenger fees, as well as taxes paid to national treasuries. By paying for the building, maintenance and use of its infrastructures, air transport gives more back to public funds than it receives. Airlines also pay over $7 billion per year in fuel- and emissions-related charges in various countries around the world.

In Europe, for example, a study by the European Regions Airline Association found that European rail is subsidised by around $60 billion a year from EU governments, whereas aviation (which mainly receives subsidies on public service routes) gets around $440 million annually.

Fleet renewal is one of the principal ways that airlines are improving their environmental performance – every new aircraft is around 20% more fuel efficient than the one it replaces. The rate at which airlines renew their fleet is naturally dependent on many factors, and has significant commercial implications for individual airlines.

More and more airlines across the world are investing in the latest and most efficient aircraft. Over 20,000 aircraft will be purchased by airlines in the next 20 years, around 40% of these new aircraft will be replacements for older less fuel-efficient aircraft. 

Different flight “phases” (such as landing, cruising, and take-off) require different engine power settings for the aeroplane. Both the amount of fuel consumed per second and the amount of emissions per unit of fuel can differ for each power setting.

So it is true to say that a plane creates more greenhouse gases when it takes off than when it is flying on its normal cruising altitude when comparing a given unit of time in each phase (i.e. a second or a minute for example).

For example, because an aircraft uses a higher power setting at take-off and climb (typically around 70% of full power) it will use more fuel and emit more CO2 (which is proportional to fuel burn). This will be more, per second, than during cruise when engines normally run at around 15-30%.

Similarly, during descent and landing aircraft engines will run at less than 30% so fuel burn and emissions per second will be much lower than during cruise or take-off and climb.

However, a comparison between the total emissions at each flight ‘phase’ is largely determined by the amount of time the aircraft spends in each phase. For most flights, cruise emissions will dominate the total flight emissions simply because the aircraft spends most of its time cruising. However, on very short flights (say less than 30 minutes) it is possible that emissions during take-off and climb will constitute the largest part of total flight emissions. 

Aviation plays a vital role in bringing fresh produce to stores and enabling consumers to have the best choice of goods; it transports goods that otherwise would not be offered in European supermarkets; it supports the economies of developing nations that would otherwise be unable to sell their produce; and it is not as damaging to the environment as many in the environmental movement would have you believe.

See the economic engine section of this website to find out more about the vital role aviation plays in world trade and development.

Transport is just one part of the food production / distribution chain – the whole chain takes us from the seed to delivery to the consumer. If you want to identify the carbon footprint of a product, other transport modes must be included in the assessment. But don’t stop there – the impact of the entire supply chain must be included, not just transport emissions. Different agricultural practices and resource requirements often mean that food produced overseas can have a much lower carbon footprint overall, even when transport is taken into account.

For example, a Lincoln University study found that lamb raised on New Zealand’s pastures and shipped to Britain produces 1,520 pounds of CO2 emissions per tonne while British lamb produces 6,280 pounds of CO2 per tonne, in part because poorer British pastures force farmers to use feed. In other words, it is four times more energy-efficient for British consumers to purchase lamb imported from New Zealand, even taking into account it being transported 19,000 kilometres by ship. In another case, a report commissioned by Sainsbury’s and World Flowers and carried out by Cranfield University showed carbon emissions from Kenyan roses, including air transport, were 5.8 times lower than for Dutch roses.

Therefore, the concept of ‘food miles’ is flawed because it is too simplistic and does not provide a meaningful measure of all the factors of production that contribute to a product’s environmental footprint. Indeed, it could actually mislead consumers who are trying to adopt more sustainable lifestyles, as the import of fresh produce can help support millions of livelihoods in the often developing countries from which they are exported. 

Quite aside from consumer choice and the ability for people to widen their food experiences, many types of produce flown to supermarkets in Europe come from developing nations. The exports of exotic fruits and vegetables are vital to the economies of many of these countries, providing income and employment in areas that do not have other industries to fall back on. For example, over one million livelihoods in Africa are supported by UK consumption of imported fresh fruit and vegetables (Mac Gregor and Vorley, 2006).

In Kenya, for example, the flower industry is the nation’s second largest export activity, making up 65% of all exports and employing over 50,000 people. Without air transport, these flowers could not be delivered to the markets of Europe. Kenyan flowers result in 5.8 times less carbon emissions than those imported from The Netherlands, including the transport.

Recently, the Geneva-based UN agency, the International Trade Centre, revealed that 83% of air freighted organic produce sold in the UK is imported from “least developed or lower-middle income developing countries”… The major exporters of air-freighted organic products, representing 70% of the market, are from the Dominican Republic, Kenya, Ghana and Egypt.