Global warming

Enormous carbon emissions

Tourism is an important source of revenue for many developing countries. Getting tourists in is usually easiest by air, making air travel account for around 40 per cent of international tourists today. The snag is that aviation is a major source of greenhouse gases.

[ By Andrea Herbst ]

The bulk of vacationers comes from rich countries in Europe and the United States. Most tourists stay in their home regions. The UN World Tourism Organisation (UNWTO) states that in 2006, tourism generated $ 735 billion, with $ 221 billion, almost a third, going ­to developing countries. Just like exports of goods, tourism generates revenues, jobs and foreign-exchange reserves.

In business terms, more tourists mean more money. The UNWTO says that “international tourism growth in the 50 least developed countries increased by 110 % from 2000 to 2007”. It considers the sector “one of the main opportunities for sustainable growth” in many developing and least-developed countries.

Environmentalists, however, dispute that this kind of growth is really sustainable. The reason is that most tourists arrive by airplane, which implies massive carbon emissions. According to UNWTO, tourism accounts for about five per cent of global greenhouse emissions. Air travel is said to make up around 40 per cent of the greenhouse emissions caused by tourism.

Airplanes have made it quick, easy and relatively ­affordable to travel anywhere in the world. But there is an environmental cost that neither passengers nor airlines cover. According to the Heinrich Böll Foundation, which is close to Germany’s Green Party, a tourist who flies from Germany to the Caribbean and back causes the equivalent of four tons. Four tons of carbon emissions, however, is the average annual emission per human being.

The biggest obstacle to finding effective solutions to the air travel problem is that the actual impact of airplanes on the environment is not fully known. They cannot be directly compared with cars or trains, for example, because they do not travel on the earth’s surface. Airplanes emit CO2 directly into the upper troposphere and lower stratosphere. Supersonic planes, which fly higher, emit straight into the stratosphere. The troposphere and the stratosphere are where carbon emissions cause the greenhouse effect.


Airplanes, moreover, not only pump CO2 into the atmosphere. They also emit nitrogen oxides (NOx), water vapour and soot into the air. Because they do so at such high altitudes, the effects on climate change are thought to be greater, though the definite details on how and why are still unknown. The Intergovernmental Panel on Climate Change’s (IPCC) 1999 special report “Aviation and the Global Atmosphere” argued for an “aviation multiplier”, estimating that air travel’s total climate impact was two to four times that of its carbon emissions.

These “extra” emissions lead to considerable uncertainty. Take, for example, water vapour. Scientists believe it adds to the greenhouse effect. The empirical ­evidence is not clear, however. After the September 11 attacks in New York and Washington, planes were grounded in the USA for three days. Scientists found that, without the water vapour contrails created by airplanes, day and night temperatures were 1.1°C higher. But why that happened and whether the reason was ­really lack of contrails remains to be discovered.

It also seems that the solution to one air pollution problem worsens another. For example, it has been suggested that reducing cruise altitudes would reduce water vapour contrails and nitrogen oxide effects. However, it would depend on burning more fuel and thus lead to more CO2 emissions. The EU will include air travel in its Emissions Trading Scheme (EU ETS) from 2012 onwards, but it will do so without using any kind of aviation mulitplier.

“Aviation produces around two per cent of the world’s manmade emissions of carbon dioxide (CO2), according to the United Nations Intergovernmental Panel on Climate Change (IPCC),” states, a website run by the Air Transport Action Group, an international lobby organisation. Duncan Clark, a journalist with Britain’s The Guardian, says this figure may be misleading. He argues that “in developed countries the slice of CO2 emissions caused by flying is higher – around 6.3 % in the UK, according to Department for Transport figures for 2005”.

Clark, however, considers 6.3 % still too low, because the aviation multiplier must be considered, and so must emissions from support vehicles. Clark argues that aviation’s true impact is probably around 13 % to 15 % of the UK’s contribution to greenhouse gas emissions. Similar calculations would apply to other countries. The share of aviation is probably particularly large in big countries where people use airplanes for domestic trips, for instance the USA, Canada or Russia.

Grasping for solutions

According to, “80 per cent of aviation’s greenhouse gas emissions are related to passenger flights exceeding 1,500 kilometres, for which there is no practical alternative”. The demand for travel is not going to disappear, so the big question is how to make aviation climate-friendly.

The challenge is more daunting than it is for road traffic. There are already energy-efficient alternatives to gas-guzzling cars, and technology is improving. Airplanes, however, require a lot of power just to take off.

Research into alternative energy sources has been done, and electric planes have been developed. Because of their engines and batteries, however, these planes are significantly heavier than conventional ones. Batteries, moreover, can only store a ­li­mited amount of energy, so the range of electric planes is quite short. Whether electric power is environment-friendly, of course, depends on how it is generated. If fossil fuels are used, there is no fundamental difference from burning fuels in airplane engines. Nuclear power is carbon-free, but causes dangerous toxic waste that needs to be kept safe for millennia.

Biofuels seem an option. But to produce enough ­fuel to fly an airplane, vast amounts of soy or corn are needed. In a world with one billion people who do not have enough to eat it seems appalling to use food to generate fuel.

Some have suggested compensating emissions caused by air travel by planting and cultivating forests. Afforestation, however, is a general “fix” that does not address air travel specifically. Forest and land-use issues are already a hot topic in international climate diplomacy, and compensating for all airplane emissions this way would only be possible if much more land was made available.

All summed up, the debate on curbing aviation emissions is a mirror image of the climate debate in general. People from developing countries pointedly ask why they should care about protecting the environment given that the rich world became rich without much regard for the issues. So long as the world’s leading economies do not do anything about reducing ­carbon emissions, they can hardly expect other countries to act.

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