Aviation emissions & reductions

Greenhouse gas emissions from aviation include carbon dioxide (CO2), as well as other polluting effects, for example, from aerosols, nitrogen oxides and contrails which all contribute to the climate crisis. Unlike emissions from other sources, such as cars or factories, it is believed that some emissions from aircraft have a far greater impact on the climate crisis due to the fact that they take place at high altitude. This additional impact is known as ‘radiative forcing’ and its historical impacts on global temperature increases could be as much as two or even four times that expected from the CO2 emissions alone.

What are airlines doing to reduce emissions?
It is in the industry’s interest to reduce aircrafts’ fuel consumption because this is one of the greatest costs of a flight. Using less fuel benefits the environment, as well as the airline’s bottom line. For this reason, there is constant research and development into new technologies that can reduce the amount of fuel needed per passenger mile. We are already seeing the difference that these technological advances can make, but the impact on efficiency is limited – The International Air Transport Association’s (IATA) own target has been 1.5 percent each year – and therefore does not negate the passenger growth of 5 percent per year.

Techniques include using lighter materials to reduce the weight of the airline; creating slimmer seats to accommodate more passengers; and adding devices to wing tips to reduce drag, meaning that less fuel is needed. These ‘winglets’ are so efficient at reducing fuel use that retrofitting them on existing aircraft very quickly pays for itself.

In-flight-meal
Photo credit: Can Pac Swire

Airlines also save fuel by reducing weight. By not serving meals to every passenger, not only are ‘no frills’ airlines not paying for the meal – but they are also not paying for the cost of carrying the meal. Multiply this across a full drinks list, entertainment screens and reduced luggage allowances – and this can constitute worthwhile fuel savings for a budget airline. A back-of-the-envelope calculation from Wired suggested that removing a single bag of peanuts from every American Airlines flight could save the company US $2,000 per year in fuel – hence the removal of snacks from many routes.

It’s not just the hardware that is being developed – software improvements are reducing emissions, too. Aircraft are frequently left in holding patterns as they circle above an airport waiting for their landing slot. Developing more efficient air traffic control systems can reduce or eradicate this wasted flight time.

These efficiency developments may seem positive. However, the flip side is that as planes get more efficient, airlines save money, prices are therefore reduced and the number of people flying increases, as do emissions. This is known as the ‘efficiency paradox’.

The type of fuel will of course have an impact on flight emissions too. Unlike other forms of transport, aircraft have unique restrictions. Their speed can’t be slowed to a more ‘efficient’ pace, fuel must be energy dense to keep weight down, and onboard renewable energy sources, such as turbines and solar panels, are simply not feasible, as they are on ships.

Tractor harvesting crops for biofuel
Photo credit: CenUSA Bioenergy

Biofuels are often cited as an example of a ‘clean’ fuel which can work on planes. They can be produced from plants such as sugarcane or corn, which are turned into ethanol and combined with petroleum to power vehicles. Algae can also be used as a source material. However, just because they are not fossil fuels, this does not mean they are carbon neutral. Using these plant-based fuels on a very tiny scale could be sustainable, but at the level required to power the world’s planes, vast areas of land would need to be set aside to grow these crops. Forests are razed to make way for plantations, and this land use change more than offsets any CO2 saving that may have been made by burning a ‘clean’ fuel. According to Transport & Environment, these food-based biodiesels are 80 percent worse for the environment than fossil fuels, on average. Alternatively, existing agricultural land may be redirected into fuel use rather than food, which threatens food security around the world. As industry’s demand for corn, for example, grows, so the crop’s price rises, pricing out poorer consumers and worsening nutrition levels in developing countries. This is why emissions calculations based on these types of fuels use net “life cycle emissions” rather than simply calculating emissions at point of use.

There are some fuel solutions – known as advanced biofuels – which convert waste products into fuel, such as vegetable oil and animal fats used in cooking processes, manure from livestock, and even some household waste. This is not futuristic technology; it’s available now. Sweden, for example, has 34 power plants that generate energy from waste – heating some 1.25 million homes. Norway will require aviation fuel to contain at least 0.5 percent advanced biofuel starting in 2020.

Although these alternative fuels can reduce emissions from aviation (indeed, 2,500 passenger flights ran with blends of up to 50 percent biofuel between 2011 and 2015), there are difficulties scaling this up to the level needed to make a real impact. Usable waste is a limited resource, and as it is already being used in some other sectors, there is a danger that its use by airlines would mean CO2 savings are lost elsewhere – resulting in no net reduction in CO2. However, as it is likely that airlines will be able to use sustainable aviation fuels to offset their greenhouse gas emissions under schemes such as CORSIA, we hope that there will be an even greater effort to accelerate the sustainable development of these fuels in coming years, as this would allow airlines to meet climate targets while still enjoying a certain amount of controlled growth in the meantime.

Written by Vicki Brown
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