Air traffic and the climate

This site presents air traffic emissions and their impact on climate change.

Air traffic comprises public transportation. Emissions from aircraft engines are similar to those of other means of transport.

On a global scale, carbon dioxide emissions (CO2) from air traffic account for roughly 2 per cent of all emissions resulting from human activities.
Other components of exhaust fume emissions have indirect warming and cooling impact on the climate.

Demand for air travel increases through increases in international contact and trade.

The aircraft technology develops and the energy efficiency and emissions in relation to traffic volumes decrease.

The aviation industry aims to control its emissions in various ways.

Air traffic emissions

What are emissions from aircraft?

The exhaust fumes from aircraft engines contain the same elements as emissions from other engines. These include, for example, carbon dioxide (CO2), nitrogen oxides (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), water vapour, sulphur oxides (SOx) and particulate matter.

Aviation petrol, i.e. kerosene, is used as fuel in jet and turbopropeller engines. Its properties are close to diesel. In the combustion process, one kilogram of kerosene yields 3.16 kg of carbon dioxide and 1.3 kg of water vapour. The amount of other emissions varies at different stages of the flight, and they are also affected by such factors as the size of aircraft and the type of engine.

Energy efficiency of aircraft

The consumption of fuel by aircraft per seat has decreased by around 70 per cent over the last 40 years.

The current rule of thumb on fuel consumption is that a long-distance flight consumes fuel in the region of 3 litres per passenger per 100 km, if the plane is full. On shorter flights, a jet passenger plane consumes fuel in the region of 3–5 litres per passenger per 100 km, if the plane is full. As part of fuel consumption is also attributable to cargo, the consumption per passenger is even lower.

Amount of air traffic emissions

In 2016, CO2 emissions from fossil fuels in the Finnish economy totalled 40 million tonnes (total emissions of greenhouse gases were 59 million CO2e (carbon dioxide equivalent)). Total CO2 emissions from domestic traffic and transport were 12 million tonnes, and CO2 emissions from domestic air traffic totalled 0.2 million tonnes.

In 2017, a total of 0.66 million tonnes of kerosene were sold in Finland to all airlines for international flights, producing CO2 emissions of 2.1 million tonnes.
On global scale total CO2 emissions from air trafiic were 859 millon tonnes in 2017. This comprises approximately 2 per cent of all emissions resulting from human activities. Emissions from maritime traffic are roughly the same. In contrast, national emissions in Germany totalled 760 million tonnes in 2014.

Emissions from individual flights

Carbon dioxide emissions from flights between different destinations can be estimated, for example, using the carbon emissions calculator of the International Civil Aviation Organization (ICAO). Certain airlines also offer emissions calculators on their websites. Links to different calculators are available in the table below. The results provided by different calculators differ slightly from one another. This can be explained by differences in initial information and the impact of the transportation of cargo. These calculators are usually based on public databases, but airlines also use their own fuel data. In addition, certain calculators aim to consider the indirect climate impact of exhaust gases other than CO2 and include it in total emissions using a specific multiplier. This makes it more difficult to interpret different calculators.

The following table presents the results of certain emissions calculators over a two-way flight.

Two-way flight One-way distance, km ICAO calculator Finnair calculator Atmosfair calculator
Helsinki - Phuket 8311 km 604 kg CO2 988 kg CO2 5264 kg CO2
Helsinki - Brussels 1651 km 372 kg CO2 371 kg CO2 996 kg CO2
Helsinki - Kittilä 823 km 189 kg CO2 162 kg CO2 436 kg CO2
Helsinki - Stockholm 400 km 127 kg CO2 123 kg CO2 250 kg CO2

Total CO2 emissions from Finnish consumption have been estimated, for example, in the survey of the Finnish Environment Institute.

Average emissions are estimated to be 11,500 kg CO2e per year. For example, a single flight to Brussels and back accounts for 3 per cent of this amount.

Impact of emissions

What effects do emissions from aircraft have?

The majority of emissions from aircraft is released at the cruising altitude (10–12 km). Carbon dioxide has the same heating effect on the atmosphere irrespective of the altitude of the emissions. The other exhaust fumes and particles from engines react in the atmosphere in a complicated way, partly increasing and partly decreasing the warming effect. Not all the reactions and effects are completely understood.

Impact of different emission components

Carbon dioxide emissions (CO2) from air traffic account for around 2 per cent and nitrogen oxide emissions (NOx) for close to 3 per cent of the total emissions produced by human activities. NOx emissions have both increasing and decreasing impact on the warming effect. At cruising altitude, NOx emissions produce ozone which warms the atmosphere. However, NOx emissions simultaneously reduce methane in the atmosphere, which is a powerful greenhouse gas. In air traffic, sulphur oxide (SOx) and particulate matter (PM) emissions are low compared to other emission sources, as the sulphur content of the fuel is low and combustion is pure. At the cruising altitude particulates increase the formation of clouds, but at the same time sulphate particles formed from sulphur dioxide have a cooling effect on the atmosphere. The water vapour (H2O) created in the fuel combustion reaction disappears from the atmosphere in 1–2 weeks.

In suitable conditions, condensation trails of water vapour remain visible behind aircraft flying at the cruising altitude. Their impact on the formation of cirrus clouds comprises part of emission effects. This effect is different during the day and during the night, and it is not yet properly understood. According to estimates, the proportion of air traffic emissions from all human activities on the warming of the atmosphere is in the region of 3.5–4 per cent. The effect is approximately double in relation to the proportion of carbon dioxide emissions from air traffic. This estimate does not include the effect of the formation of cirrus clouds, which is not yet sufficiently well known.

Emissions have no effect on the ozone layer

The ozone layer in the upper atmosphere, i.e. the stratosphere, protects the Earth from ultraviolet, i.e. UV, radiation. Emissions of nitrogen oxides from air traffic are released in the troposphere and lower layers of the stratosphere, where they react with oxygen and produce ozone. Civil aircraft do not, therefore, reduce the ozone layer protecting the Earth.

Reducing emissions from air traffic

Although passengers nowadays fly to their destinations with increasingly small amounts of energy, the increase in air traffic is increasing the consumption of energy and emissions worldwide, unless action is taken. Developing engine technologies, more efficient uses of airspace, low-emission flight methods and financial control measures can help to improve emission efficiency. Renewable fuels and electricity may also play important parts in the future.

The development of emissions is also controlled by financial means, the most important of which is the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) to be deployed globally starting from 1 January 2019.

The development of aircraft technology

The ICAO specifies the limits for emissions from aircraft. This, together with the rising costs of fuel, is guiding the aviation industry to construct aeroplanes that are more efficient and produce lower emissions.

The consumption of fuel per passenger and per kilometre travelled is approximately 70 per cent more efficient than 40 years ago. Improving energy efficiency will be slower in the future, but several technological development programmes are underway, such as the Advisory Council for Aeronautics Research in Europe (ACARE).

During the past decade, the energy efficiency of air traffic has improved by more than 1 per cent per year. Renewable fuels offer means to reduce emissions from aircraft. Suitable products already exist and they have also been tested, but their expanded use requires continuous production and cost management.

The use of electric power on commercial aircraft is being developed on several fronts. The first electric light aeroplanes are already in production, and Finland has also acquired one. For example, the large aircraft manufacturer Airbus is actively developing hybrid aircraft. Electric aircraft is expected to be ideal for domestic traffic where distances are only hundreds of kilometres.

More efficient use of airspace

The consumption of energy and emissions from air traffic can be reduced in other ways, for example, by developing air traffic control procedures and routes so that air traffic flows as flexibly as possible and without delay. The efficient use of airspace and the movement area will reduce unnecessary taxiing, holding and idling of engines in both air and ground traffic.

By making the use of airspace more efficient it would be possible to reduce one-time emissions by a few per cent. Eurocontrol, the European Organisation for the Safety of Air Navigation, has developed procedures for assessing emissions from air traffic in various airspace solutions.

The management of air traffic in Finland is more efficient than in Central Europe because there is no congestion and the airspace is used flexibly for the needs of both civil and military aviation.

Low-emission flight methods

Energy efficiency can be improved by optimising the flight speed and cruising altitude. In continuous descent operations (CDO), an aeroplane descends from the cruising altitude without any horizontal flight phase, which reduces fuel consumption and emissions, as well as noise. Using this method, a narrow-bodied aeroplane can save as much as 100 kg of fuel, reducing CO2 emissions by 320 kg.

Suitable fleet for different routes

Domestic flights in Finland often use planes powered by turbopropeller engines, which consume much less fuel than jet engines. For example, a full ATR-75 turbopropeller plane flying from Helsinki to Joensuu uses from 2–3 litres of fuel per 100 passenger kilometres. Roughly one quarter of all flights to and from Helsinki Airport are carried out using turbopropeller planes.

Control measures to reduce emissions

Financial control measures

Various financial means have been proposed to reduce emissions, requiring either political decisions or determination according to market mechanisms. Political solutions include taxes and fees that would primarily have an impact through reducing demand. Market mechanisms include emissions trading for air traffic, which has been carried out in the EU since 2012, and CORSIA which will enter into force starting from 1 January 2019.

CORSIA

In the Kyoto Protocol (1997), different countries agreed that they will strive to reduce emissions from international air traffic and shipping by working through the worldwide UN umbrella organisations in the sector (ICAO and IMO). The ICAO is an organisation under the UN which has 192 member countries. Provisions on technology and air safety in civil aviation are based on the ICAO’s standards and recommendations, likewise the commercial rules for the sector.

The ICAO extensively prepared global measures to reduce carbon dioxide emissions from air traffic and, in October 2016, its assembly decided on the principles according to which CORSIA (Carbo Off-setting and Reduction Scheme for International Aviation) will be built to freeze net emissions at the 2020 level using offsetting mechanisms.

Air traffic will grow carbon neutrally starting from 2020

The ICAO’s CORSIA is based on detailed emission reports prepared by airlines, on the basis of which airlines are ordered to make investments in emission-reducing projects in other sectors, insofar as their emissions from international traffic increase. Aviation is the first sector to deploy a global scheme for the management of carbon dioxide emissions. Starting from its deployment, the scheme covers 76 per cent of all international flights (including the UAE and the USA), and its coverage will increase gradually. Emission offsetting will start from the beginning of 2021.

Trafi is responsible for the implementation of CORSIA in Finland. Its website offers more information about the scheme.

Emissions trading in the EU

Trading on air traffic emissions started in the EU on 1 January 2012. It covers all flights inside the EU and the EEA. Air traffic emissions rights are scarce, due to which airlines have acquired emissions rights through auctions or from other sectors. Trafi is responsible for the arrangement of air traffic emissions trading in Finland. Its website offers more information about the trading procedure.

The EU emissions trading scheme is valid until further notice, and the EU will later decide on its future and coordination with CORSIA.

National control measures

National control measures do not have any significant impact on air traffic, as flights are mostly international and traffic is regulated on the basis of international agreements.

The tax exemption of aviation fuel has been agreed upon internationally, and it is considered to be impossible to change this on international flights. Maritime traffic is regulated by a similar international agreement which also applies to domestic traffic in Finland. Not many countries have implemented any national solutions for taxation on aviation fuel.

Certain EU states have imposed a tax on air travel, justified mostly on the basis of governmental tax revenue. In the Netherlands (2008) and Sweden (2018), taxation on air travel has also been explained by lower emissions achieved through lower demand. In the Netherlands, this tax was cancelled in 2009 due to its adverse financial impact. In general, taxes cannot be allocated to measures aimed to reduce emissions.

The air traffic infrastructure (airports, air navigation services and equipment) are funded by service fees and commercial income. This in part increases air traffic costs and has an impact on service prices and demand.

Further information

Emissions

Emissions control

Trafi Aviation

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