Flying beyond our means – air travel and the environment

Key text

That's because one of the four engines of the plane was flying on a mix of biofuel made from plant-based material – in this case, coconut and babassu palm oil. This test flight was hailed as the world's first commercial flight powered (partly) by biofuel, with the ultimate aim of trying to reduce carbon emissions into the atmosphere.

It might have been a public relations coup for the airline, but environmentalists criticised it as a publicity stunt saying there are only scant savings to be made using biofuels, especially if food crops are forgone to produce the fuel. Some even went so far as to label the exercise as 'high altitude greenwash'.

Then in November 2008, with much less fanfare, a small jet flew on a test flight across the United States on 100 per cent biofuel for 2,858 kilometres of the total 4,000-kilometre journey.

Greenwash or not, what both flights achieved was to focus attention on the great air race underway around the world to address the environmental effects of flying.

There are good reasons why airlines are trying to be 'greener'. With passenger numbers soaring, the emissions from domestic flights over Australia are growing faster than any other method of transport. In Australia, the number of people flying is predicted to double within the next 20 years. Over 23 million passengers – more than the country's entire population – flew on international flights in and out of Australia in the 12 months prior to August 2008. Fifty million people flew on domestic and regional flights.

Just one return trip between Sydney and London produces around 5.7 tonnes of carbon dioxide per person, about the same as the average Australian produces from their combined car and electricity emissions over an entire year.

The story is similar around the world.

Aviation contributes about 3.5 per cent of radiative forcing (global warming) and – according to the Intergovernmental Panel on Climate Change – is likely to increase to 5 per cent by 2050 for a mid range scenario, thus making air travel a significant source of man-made climate change (Box 1: What aviation emissions do).

Concerns such as these have resulted in governments, scientists and the airline industry trying to find better, 'greener' ways of flying. Alternative fuels, flight path management and more efficient plane design are just some of the areas of research (Box 2: Flying smarter).

It's also making many people and businesses re-think how and where they fly, and whether they need to fly at all (Box 3: Saving our skies – what can we do?).

The environmental effects of aviation

It's not just emissions that are the problem; aviation has a range of effects on the environment.

For starters, planes can cause considerable noise pollution, which in Australia has led to four major airports banning flights between 11pm and 6am. For local residents, at around 95 decibels every time a plane takes off it is equivalent in noise to a truck passing close by. But things are improving; the new 787 noise levels are around 10 decibels lower than the older aircraft they are replacing. According to the International Civil Aviation Organisation, noise is the biggest environmental issue with aviation for local communities. Aircraft noise affects the quality of life of residents around airports in some cases causing problems with sleep, communication, learning and even cardiovascular function.

Air pollution can also be a problem, affecting air quality for hundreds of kilometres downwind from an airport.

It's not just the planes that leave a footprint, so do the airports. There are land use, planning and ecosystem concerns at the local level as large areas of land have to be set aside for the airports and their related access roads and infrastructure.

Recent modelling by Airport Footprints Ltd for one UK airport shows that flights are responsible for 85.9 per cent of the airport's ecological footprint, with ground transport vehicles (including staff and passenger access and service vehicles and cargo trucks) responsible for another 9.5 per cent. Other demands on the environment include catering facilities, utilities such as energy and water use, built land and waste facilities.

The heavy footprint of an airport

Sector	Percentage of airport ecological footprint (%)
Flights	85.9
Ground transport	9.5
Food	0.9
Utilities (energy & water)	1.5
Waste	1.9
Built land	0.2

Source: Marcus Sutcliffe, Airport Footprints Ltd

In the northern hemisphere, de-icing operations are being examined as the chemicals used to keep planes and run-ways ice-free can have harmful effects on ground water and surface water ecosystems.

Other critics add that aviation – by providing access to previously untouched parts of the world – can be responsible for pollution in previously pristine locations such as the Antarctic. And by opening the door to tourism and other developments, aviation can unwittingly help spread animal and plant diseases.

But the largest environmental impacts can't easily be seen. That's because they take place well above the Earth. According to the Australian Government Department of Climate Change, the domestic aviation industry accounted for around 6.1 million tonnes of carbon dioxide equivalent (Mt CO2-e) of greenhouse gas emissions in 2006. This represents only 7.7 per cent of all transport emissions, but aviation is one of the fastest growing contributors of greenhouse gases. While greenhouse gas emissions from transport increased by 27 per cent between 1990 and 2006, emissions from the domestic aviation industry increased more than 107 per cent.

Complicating the issue of aircraft emissions is that they have been largely unregulated. International emissions (about 50 per cent of the global total) are exempt from the Kyoto Protocol governing reductions in greenhouse gases (they will be included in the European Union's emissions trading scheme from 2012). In addition, there is no tax on airline fuel at an international level. That means there's no pool of money to help counter the adverse environmental effects of aviation, and the lack of a fuel tax can be seen as an incentive for people to travel by air, by keeping fares lower.

Peering over the horizon

Like other countries, Australia has been trying find better ways to ensure that the aviation industry reduces its footprint.

In early 2008, the Australian Government announced it would draw up a National Aviation Policy Statement, to guide the industry's growth over the next decade and beyond. This will address the environmental concerns arising from the growing number of planes in Australian skies, as well as tie in with the efforts of international bodies such as the International Civil Aviation Organisation. It will also look at the need for market-based measures such as emissions trading or carbon offset schemes in the aviation industry.

What is certain is that a range of measures will be needed – technological advances such as biofuel blends and more efficient plane design are not enough to stop the rapidly growing impact of aviation on the environment.

Related Nova topics:

Carbon currency – the credits and debits of carbon emissions trading

Making our mark – ecological footprints

Quiet please! Fighting noise pollution

Local air pollution begins at home

Cleaner production – a solution to pollution?

Box 1: What aviation emissions do

Although aviation only contributes around 2.5 per cent of annual global carbon dioxide emissions, emissions at altitudes of 9 kilometres or more have a much greater effect than if they were at ground level because of the non-carbon dioxide emissions. And at supersonic altitudes it's even worse, the radiative forcing – greenhouse effect – is five times greater than for planes travelling at the lower subsonic levels because of the water vapour emitted into the naturally dry stratosphere.

Modern planes are responsible for a cocktail of emissions that can affect the environment at the regional level where they fly, as well as contribute to global warming. When jet engines burn fossil fuels – generally kerosene – the main discharges that affect climate include carbon dioxide, nitrogen oxides, soot, water vapour and sulfate particles.

Click on image for a larger version

Carbon dioxide is a greenhouse gas that contributes to global warming. Of particular concern is that carbon dioxide can remain in the atmosphere for up to 200 years and longer, and spreads in a blanket around the Earth.

Nitrogen oxides emitted from jets have two main effects. Firstly, they break up methane gas present in the skies. Methane is a greenhouse gas that spreads out around the globe, so reducing it reduces global warming slightly. Secondly, nitrogen oxides also react in sunlight to create the greenhouse gas ozone, which has a localised warming effect. At tropical latitudes the production of ozone occurs five times faster than in temperate zones. Because the two reactions involving methane and ozone occur in different regions, they do not simply cancel each other out.

Water vapour and particles from planes in cold air trigger the formation of distinctive condensation trails (contrails) seen so often trailing behind planes in the sky (most of the water content of contrails is actually condensed from the background atmosphere). Contrails that persist may eventually form the wispy looking cirrus clouds that can last for weeks in the atmosphere. Contrails and cirrus clouds act to trap the Earth's heat on a regional scale. Cirrus clouds also reflect some of the heat from the sun away from the Earth, in what's called the albedo effect. However, the warming effect of these clouds seems to be greater than the cooling effect. In fact this warming effect may be as large as that from carbon dioxide emissions from planes. Researchers are trying to clarify the effects of contrails and cirrus clouds created by planes.

Soot and sulfate particles have little direct effect in comparison to other emissions. Soot has a small warming effect and sulfate particles have a minor cooling effect on climate. Both can trigger cloud formation though, so indirectly cause warming.

Related site

• Does flying cost the earth? Animation (Science Museum, UK)

Box 2: Flying smarter

Cleaner fuels

Two of the main advantages of kerosene are that it is energy rich (important when a plane has to carry its fuel long distances) and doesn't readily freeze at the low temperatures of cruising altitudes (less than -40ºC). Unless an easily produced fuel with similar properties is developed, kerosene is expected to remain the main jet fuel for decades to come. Testing of biofuels produced from coconuts, Jatropha, algae and other sources is underway but the technology needs further development. Nevertheless, biofuels for aviation can be produced through several processes: fermentation, transesterification and the Fischer-Tropsch process used by Germany in World War II to overcome oil shortages.

Biofuels are divided into two categories: first and second generation biofuels.

First generation biofuels are those that are currently being produced commercially using existing technology. These fuels are produced from crops such as corn, wheat, sugar cane and oilseed crops. But there's increasing concern that first generation biofuels take up valuable land and resources needed to grow food.

Second generation biofuels, on the other hand, rely on promising technologies that are currently being developed for commercial use. They can be made from waste biomass – such as leftover food crop materials including straw or even woodchips. Weeds and dedicated woody energy crops can also be used.

Some commercial airlines are promoting their use of biofuels made from crops that don't compete with food production such as Jatropha, babassu and algae. Air New Zealand for instance, is testing a Boeing 747-400 with one of the plane's four engines running on Jatropha oil. Jatropha plants can be grown on non-arable land and its seeds contain up to 40 per cent oil. But to get commercial yields, Jatropha is sometimes grown on more productive land with the addition of fertilisers and water. In Australia Jatropha curcas has been banned from importation due to its classification as a potential weed.

On the other side of the world, a Dutch airline is trying a different biofuel – made from algae – to fully power its Fokker F-50 planes by 2010. Algae are a promising example of a second generation feedstock for fuel that can be made using ponds of seawater. But further development of the technology is needed, and large areas would have to be set aside to grow the algae.

Although the technology is improving, current biofuels can be limited in their greenhouse gas savings, and can require huge areas of land to grow the biomass. According to one estimate, it would take some 1.4 million square kilometres – more than twice the size of France – to produce enough Jatropha oil to power the world's planes for a year.

New technology

When a two-seater motor-glider with a 16-metre wingspan and propeller took to the skies south of Madrid in April 2008, it represented a new era in aircraft design – one that produced zero carbon dioxide emissions.

Developed by Boeing and several international partners, the Fuel Cell Demonstrator Airplane climbed to over 300 metres powered by hydrogen fuel cells and lithium-ion batteries.

It then cruised at 100 kilometres an hour for a total of 20 minutes, powered only by the fuel cells that converted hydrogen into electricity and heat with the only exhaust being water. But as a greenhouse gas, the emission of larger amounts of water into the atmosphere is of concern. At what point in the future such planes could become a commercial reality is unclear and whether this technology will ever be suitable for large heavy passenger-carrying planes.

Better designs

Many airlines are looking at more efficient plane design to reduce fuel consumption including lighter composite materials, more efficient wings with less drag, and even using continuous welds in place of rivets to hold planes together.

Qantas calls the latest addition to its fleet, the Airbus A380 super jumbo, the 'jolly green giant'. Qantas claims the giant plane has 50 per cent more floorspace than a 747, is 25 per cent more fuel efficient than other large jets, and will need fewer flights than other airlines to move the same number of people.

KLM and others are using vertical 'winglets' at the end of plane wings to improve aerodynamics and claim it can reduce carbon emissions by up to three per cent.

But good ideas take time to take to the air. A general rule of thumb is that new designs might take 10 years to develop, and a further 10 to construct and phase in. Moreover, a given new design will have a certain production lifetime and a subsequent retirement phase. Which means there could be a lag of up to 40 years in which older-style planes would still be used.

Changing flying habits

The International Air Transport Association, the body that represents some 230 airlines, suggests that aviation's effect on climate change could be addressed through combined air traffic systems, shortening routes, better fuel management practices, and improving air navigation. In Australia, such measures are already being looked at.

In 2007, Airservices Australia, which is responsible for air traffic control, initiated a range of ways to reduce greenhouse gas emissions from aviation. These include:

• better management of aircraft on the ground, with engines off or at reduced power, before departure
• better prediction and management of aircraft delays and arrivals, rather than see planes waste fuel circling an airport in a holding pattern, and
• allowing continuous descent approaches that let planes descend at low power, saving as much as 400 kilograms of fuel per arrival.

Research conducted through the University of NSW has already shown a substantial reduction in aircraft noise and emissions by adapting flight paths of aircraft.

Related sites

• Biofuels in Australia – an overview of issues and prospects (Rural Industries Research and Development Corporation, Australia)

• Biomass – the growing energy resource (Nova: Science in the news, Australian Academy of Science)

• Aircraft emissions (Airservices Australia)

• International Air Transport Association, IATA
  • Building a greener future
  • Fact sheet: Alternative fuels (Note: the classification of biofuels in this fact sheet differs from the above classification)

Box 3: Saving our skies – what can we do?

That's not a desirable solution from the aviation industry's point of view, but the idea is already on people's radar.

Conferencing by phone, video or web-casting is one way that companies are looking to reduce the time, cost, and inconvenience of having staff fly interstate or overseas for meetings.

British Telecom saved 97,000 tonnes of carbon dioxide – and A$560 million – in one year by replacing meetings with video conferencing. In Australia, Telstra claims nearly half of all air travel is for business purposes, and that firms could save time, money and 2.4 million tonnes of carbon dioxide equivalent a year through high-definition video conferencing.

Telecommuting – or teleworking – where people work away from their firm's office (often from home) can also be used in some cases to reduce air travel.

People who still need to fly can use online carbon calculators to determine how much carbon their flights produce and purchase carbon offsets for those emissions. Many airlines already have schemes that allow passengers to pay an amount to offset the emissions created by their travel.

Critics point out that offset schemes only deal with the carbon problem after it has been created, and are in danger of being regarded as 'feel good' measures. Carbon calculators vary broadly in their estimates of emissions and there is also no regulatory system to ensure that the offsetting schemes achieve what they promise.

Perhaps the simplest ways to reduce the carbon footprint of your trip is to re-think how you travel to your destination, where you fly to, and whether you fly at all.

A flight in the tropics has a different effect to a flight in the mid-latitudes. Nitrogen oxides emitted from aircraft increase ozone and reduce methane, two gases that have a warming effect. But in the tropics the brighter sunlight creates ozone five times faster than at other latitudes increasing the warming effects.

Short-haul flights typically make disproportionately large carbon emissions. One UK study showed that a flight of 500 kilometres (around the distance from Sydney to Canberra and back) uses more than 20 per cent of its fuel in taking off and landing.

There are often more environmentally friendly travel options. Replacing flying with other means of transport such as rail can more than halve your trip's carbon emissions. For example a flight from Sydney to the Gold Coast would produce around 0.3 tonnes of carbon dioxide compared to 0.1 tonne by rail.

Related sites

• What difference can we make? (Nova: Science in the news, Australian Academy of Science)

• Climate action: Get energy efficient (Sustainable Development International/United Nations Environment Program)

• Towards a high-bandwidth, low-carbon future (Climate Risk, Australia)

Activities

• The Science Museum (United Kingdom)
  • Can technology help make planes greener? – students learn about technologies that reduce the environmental impact of planes by playing an online game.

• National Aeronautics and Space Administration (NASA, USA)
  • Contrail education – an extensive resource on contrails. Includes information, activities and lesson plans.

  Friends of the Earth (United Kingdom)

  • Lesson plan: Transport – students learn about environmental issues associated with air transport then debate the pros and cons of airport expansion.
  • Transport: The way to go – an information booklet for use with the above activity. The booklet focuses on the negative effects of transport and what we can do to reduce our impact.

  Northeast Sustainable Energy Association (USA)

  • Travel solutions to global warming – students investigate the carbon cycle and fossil fuels then suggest ways to reduce travel-related carbon emissions. Suitable for younger students.

Further reading

Australian Academy of Science
August 2010
The Science of Climate change: Questions and Answers.
A document summarising the current understanding of climate change science for non-specialist readers.

New Scientist

8 June 2009
Train can be worse for climate than plane (by Catherine Brahic)
Reviews the findings of a study that examined the life-cycle emissions of different types of transport.

13 August 2008, pages 34-37
Green fuel for the airline industry (by David Strahan)
Examines the need for and the development of suitable biofuels for aviation.

Useful sites

Provides information on the environmental impacts of aviation.
http://www.sciencemuseum.org.uk/antenna/flying/

Australian Broadcasting Corporation

• Boost for biodiesel potential (ABC Radio National, 13 December 2009)
  Describes Australian technology to produce jet biofuel from abattoir fat.
  http://www.abc.net.au/rn/scienceshow/stories/2008/2441773.htm

• The last environmental taboo (Ockham's Razor, 3 August 2008)
  Looks at the environmental costs of air travel.
  http://www.abc.net.au/rn/ockhamsrazor/stories/2008/2320462.htm

• Hydrogen considered as a fuel for air transport (The Science Show, 29 March 2008)
  Discusses the proposed use of hydrogen in the A2 jet plane and its environmental consequences.
  http://www.abc.net.au/rn/scienceshow/stories/2008/2201789.htm

Transport and mobility (Quantify, European Union)

Provides clear information on the effects of transport, including aviation, on climate.
http://www.atmosphere.mpg.de/enid/2e23729db45436b1de42bbb69c09d6aa,0/quantify/Transport___mobility_4wt.html

IPCC special report on aviation and the global atmosphere (Intergovernmental Panel on Climate Change)

Covers the effects of aviation emissions on the global atmosphere and climate, aviation technology and mitigation options.
http://www.ipcc.ch/ipccreports/sres/aviation/index.htm

ICAO environmental report 2007 (International Civil Aviation Organisation)

A detailed report that covers the outlook for aviation and its effects including aircraft noise and emissions. Part four includes a clear overview of global emissions.
http://www.icao.int/icao/en/env/pubs/Env_Report_07.pdf

The environmental effects of civil aircraft in flight (Royal Commission on Environmental Pollution, United Kingdom)

Provides detailed information on air transport and the effects of aircraft on the environment.
http://www.rcep.org.uk/avreport.htm

Sustainable aviation 2030 (Institute for Public Policy Research, United Kingdom)

Discusses the sustainability of aviation in the United Kingdom and ways to reduce its impacts.
http://www.ippr.org.uk/uploadedFiles/projects/s_a_2030_discuss.pdf

Managing aircraft and airfield de-icing operations to prevent contamination of drinking water (Environmental Protection Agency, USA)

Provides an overview of de-icing operations for aircraft and airfields and management options.
http://www.epa.gov/safewater/sourcewater/pubs/fs_swpp_deicingair.pdf

Glossary

babassu. A palm tree that grows naturally in Brazil and produces a seed similar to the coconut that is rich in oil. The oil of the babassu seed can be used for cooking, cosmetics and fuel production.

biofuel. Biofuels are fuels such as bioethanol or biodiesel made from plant or (less commonly) animal material and food waste. They are promoted as a renewable energy source without the environmental impacts of fossil fuels. But using annual land-based crops such as sugar cane and corn for biofuel production can be relatively energy inefficient and also competes with food production. Algae have been suggested as an alternative source of biomass which could overcome these problems. For more information see Biomass – the growing energy resource (Nova: Science in the news).

biomass. A general term for material from living things such as plants, animals, fungi, bacteria and food waste. Taken together, the Earth's biomass represents an enormous store of energy. Since biomass can be regrown, it is a potentially renewable resource. For more information see Biomass – the growing energy resource (Nova: Science in the news).

carbon offset. A means of reducing the impact of greenhouse gas emissions. Individuals and companies can purchase offsets to counteract their emissions from transport, electricity use etc. For example, many airlines allow customers to purchase carbon offsets to compensate for the emissions from their plane trip. The offset money is invested in projects that reduce greenhouse gas emissions such as renewable energy, tree planting or energy efficiency projects.

decibels (dB). One tenth of a bel. A unit used to measure sound intensity or power. One decibel is around the smallest change in sound that the ear can detect. Two power levels P₁ and P₂ differ by n decibels when:

emissions trading. A means of controlling greenhouse gas emissions from organisations and companies. Commonly the government places a limit on the total amount of carbon or greenhouse gases that can be released. It then provides a number of carbon 'permits' equal to the set limit. Companies then compete against each other to buy these permits. For some companies it is cheaper to develop cleaner production technologies (or reduce emissions) than to buy the permits.

fermentation. The chemical conversion of carbohydrates into alcohols or acids by microorganisms. Often fermentation refers to the conversion of sugar to ethanol and carbon dioxide by yeast according to the following equation:

Fisher-Tropsch process. A process that can be used to convert coal, natural gas, and low-value refinery products into fuel. Fischer-Tropsch fuel is colourless, odourless, low in toxicity and has fewer emissions than conventional diesel. The Fischer-Tropsch reaction converts carbon monoxide and hydrogen, in the presence of a catalyst, to high molecular weight hydrocarbons.

fuel cell. A cell that converts energy from chemical reactions directly into electrical energy. A simple fuel cell 'burns' hydrogen in a flameless chemical reaction with oxygen to produce electricity. For more information see Fuelling the 21st century (Nova: Science in the news).

Jatropha. A group of plants, shrubs and trees that can grow in dry, less productive land. Jatropha curcas seeds contain up to 40 per cent oil which can be used for biofuel. Because Jatropha grows on land of lower productivity, it is sometimes considered to be a biofuel that does not compete with food growing land and resources. However, commercially viable production of Jatropha can still use productive land, water and fertilisers. Jatropha curcas is considered a potential weed in Australia.

Kyoto Protocol. This working agreement of participating countries commits developed countries to reduce their emissions of six greenhouse gases by at least 5 per cent of 1990 levels by 2012. The Kyoto agreement became legally binding on 16 February 2005 when 132 signatory countries agreed to strive to decrease carbon dioxide emissions. More information can be found at the official The Kyoto Protocol site.

radiative forcing. A measure of the effect of a climatic factor (eg, greenhouse gases, cirrus cloud) on the balance of incoming and outgoing energy in the Earth-atmosphere system. This can be used to assess the factor's impact on climate change. Positive forcing tends to warm Earth's surface while negative forcing has a cooling effect. Forcing values are expressed in watts per square metre (Wm^-2).

subsonic. Movement at less than the speed of sound. Most aircraft travel at subsonic speeds.

supersonic. Movement at greater than the speed of sound. Supersonic aircraft include military aircraft and Concorde (which ceased operation in 2003). At these fast speeds, air ahead of the plane is compressed, shock waves form and drag increases. Supersonic aircraft often fly at higher altitudes where the density of air is lower to reduce drag.

transesterification. A process that converts animal fats or more commonly plant oils to biodiesel. The oils (or triglycerides) are reacted with an alcohol such as ethanol in the presence of a catalyst such as sodium hydroxide. This converts the triglycerides to esters (the biodiesel) and glycerol. The biodiesel produced is used in ground transport but usually cannot be used as an aviation fuel due to its high freezing point.