Aviation is coming under fresh attack from environmental lobbyists.

Andrzej Jeziorski/Berlin

There was an air of apologetic embarrassment about environmentalist Karl Schallabock as he gave his presentation on air transport and the environment at the Berlin Climate Summit in March.

The audience at the Air Traffic and Climate Protection forum consisted, for the most part, of tight-lipped and sceptical airline representatives who were less than enthusiastic as the speaker gingerly put forward the idea of forcing passengers to wait longer at terminal gates to discourage them from flying. The figures put forward by Schallabock and the forum's sponsors, the German League for the Conservation of Nature and the Environment (DNR), in support of their demands to rein in the growth of air transport, were described by one senior atmospheric scientist as "idiotic"; the research generating these figures was dismissed by Lufthansa as "frivolous".

Outnumbered and ill-at-ease, Schallabock nevertheless proceeded to present the findings of his study, carried out at the Wuppertal Institute for the Climate, the Environment and Energy, titled "Air Traffic and the Climate - a Key Problem".

In the study, he points out that air traffic is the fastest-growing sector of the transportation industry, with a correspondingly high growth rate in emissions. He expresses concern about encouraging growth with fare structures which often underbid the "greener" railway network (particularly now, with Germany's continuing domestic fare war), expansion of airport capacities and aggressive marketing.

Schallabock points out that while technological advances may have cut fuel consumption per passenger kilometre in half during the past 30 years, overall growth means that the total energy consumed by air traffic has increased "20 to 25-fold" since 1960. He argues that, while air traffic - catering to about 5% of the world's population - is only thought to be responsible for 2.6% to 2.7% of global carbon dioxide emissions, this is disproportionately high considering that India, with one-sixth of the world's population, only consumes 2.5% of the world's energy (although the validity of comparing worldwide emissions of a specific gas with the energy consumption of a Third World country is perhaps questionable).

The study goes on to assume a model where global CO2 emissions increase by 2% per annum and air traffic grows by 7.5% per annum (in fact this is the traffic growth rate in Germany alone - the worldwide rate is lower), predicting, as a result, that within five years, aircraft will be responsible for 4% of global CO2 emissions. Schallab"ck justifies his assumptions by saying that the margin for error in traffic growth predictions "is considered very wide".


Air traffic "is considered to be particularly harmful", he says, because exhaust gases, including nitrogen oxides (NOx) and water vapour, are emitted into high atmospheric strata. This is true, but the extent of the damage to the upper atmosphere is not yet fully understood, and needs to be clarified.

Even without quantifying the damage to the upper atmosphere, Schallabock says that the effects of high-altitude emissions can "be assumed to be greatly in excess of what is suggested by the simple share of energy use and CO2 emissions". He then proposes a hypothesis based on the rather broad assumption that everyone who travels by air has "by that very act used up his or her climate-relevant pollution account", leading to the conclusion that air traffic is responsible for 5% of all the world's climate-relevant pollution.

The researcher himself describes his report as "a simplified representation of the problem", serving as an "indication of the necessity for a more detailed analysis". Such analyses are being carried out by research institutions around the world, and it is doubtful whether a report containing as many questionable assumptions as Schallabock's advances the debate.

Nevertheless, in Berlin the study was backed by the DNR, which pointed out that some models give air traffic a 24.3% share of transport-related emissions which could potentially affect the climate, and furthermore asserted that "the projected increase [in energy use by air traffic] by the year 2005 is 180%".

This last figure collapses under close scrutiny. It was quickly and firmly rebuffed at the Berlin forum by International Air Transport Association (IATA) environmental coordinator Leonie Dobbie, who pointed out that it was based on an assumption that no further technological advances would be made in the reduction of engine emissions. The International Civil Aviation Organisation (ICAO) in fact predicts a 65% increase in aviation fuel consumption between 1990 and 2010, while some researchers believe that the development of cleaner engines should allow Nox emissions to be kept constant, even as annual fuel consumption - now standing at some 180 million tonnes - doubles.

Yet the DNR maintains that air traffic growth must be reined in. "The truly explosive development of air traffic and the associated burden on the climate and the environment are not a factor in the minds of the national decision makers. It is high time for a broad worldwide public debate and for serious action on air traffic," says DNR director Helmut Roscheisen.

The League concludes its attack with a series of demands to alleviate the perceived environmental threat: higher airport fees, depending on the environmental impact of the specific aircraft; an international - at least European Union-wide - aviation-fuel tax; and the curtailment of airport expansion by "a major transfer of short-distance traffic to the rails".


It is not surprising that the air-transport industry reaction to the criticisms has been downright hostile. Not that the airlines and researchers deny that there is a problem, but they do feel that the environmental groups are trying to achieve their goals by scaremongering rather than reasoned argument.

There is no doubt that aircraft emissions do contribute to environmental damage. According to Professor Ulrich Schumann, director of the DLR's Institute for Atmospheric Physics, aircraft emissions of CO2 "add linearly to emissions from other sources" and contribute to global warming.

High altitude stratospheric Nox emissions are expected to cause ozone depletion, while lower stratospheric and tropospheric emissions cause ozone formation. Ozone in the upper troposphere and lower stratosphere acts as a potent greenhouse gas. According to IATA's environmental review, the point at which the effect of Nox emissions crosses over from ozone creation to ozone destruction is generally in the lower stratosphere "near the main flight routes". This leads to considerable uncertainty about the real effects of aircraft Nox.

Emissions of water vapour, while 10,000 times less damaging than other greenhouse gases, have an environmental effect in the formation of contrails and cirrus clouds - which have a cooling effect from their shadows, and a warming effect by blocking the Earth's infra-red emissions.

IATA's first environmental review, published earlier this year, also highlights carbon monoxide (CO), volatile organic compounds such as unburned hydrocarbons, soot and other gases such as sulphur dioxide (SO2) as potentially harmful emissions - although the effects of these are only felt in the vicinity of airports.

The question still remains about the extent and precise effects of this damage on our climate. At the moment, Schumann says that the calculated contribution of aircraft exhausts to the greenhouse effect remains so low - at about 0.1¡C - that it is unprovable by measurement. Water-vapour emissions are believed, according to satellite evidence, to have increased cloud cover over Central Europe by about 0.4%.

In themselves, these are not frightening figures, but IATA acknowledges that aviation may in future have a far more significant atmospheric impact. Extrapolating ICAO's fuel-consumption trend, CO2 emissions from global subsonic aviation rise from 554 million tonnes in 1990 to 957 million tonnes in 2015. Long-term estimates suggest that by the year 2100, aviation could be responsible for up to 14% of the world's anthropogenic CO2 emissions.

Some 22 different research projects, worth some $201.6 million, on the climatic effects of aviation are being run worldwide. These are mostly sponsored by countries or regions, which manufacture the aircraft and engines responsible for the emissions under investigation. Within these programmes, six IATA member airlines are now operating commercial aircraft with sensors and analysis equipment fitted.

One such project is called Measurement of Ozone, by Airbus In-Service Aircraft. This was an initiative of the Airbus consortium, joined by French, German, Spanish and UK research institutes, these partners covering just over half the cost of the $3.6 million programme, with the EU paying for the rest. Five operational Airbus A340s, flown by Air France, Austrian Airlines, Lufthansa (two aircraft) and Sabena, have been used since 1993 to make ozone and water vapour/temperature measurements along long-haul routes. The project is to be concluded in 1995.


Hope for more new data, has come with the first flight of the Grob Strato 2C high-altitude research aircraft on 31 March. This aircraft will be able to carry two pilots and four scientists with 1t of cargo on 48h missions at 59,000ft (18,000m), and can operate for 8h at 78,700ft. The unique government-sponsored aircraft is expected to have its first high-altitude trials in late June, and is likely to be ready for operational use by the DLR in two years.

Until the results of these various current and future research programmes are available, IATA says that there remains "considerable doubt surrounding the scientific basis for policies to control aviation emissions". For now, the question is whether precautionary action should be taken, or prepared for, in case the eventual results do show that air transport has a significant atmospheric effect.

Engine-emissions standards are now defined by ICAO Annex 16, which was developed following concern over emissions at airports. It covers smoke, hydrocarbons, carbon monoxide and Nox, but does not address the issue of CO2. The ICAO Committee on Aviation Environmental Protection is now considering introducing standards to cover the climb and cruise phases of flight - but these are very difficult to measure, and vary depending on aircraft type and speed - and is also considering aircraft-emissions certification in addition to engine certification.

Considering that technological improvements will not solve the whole emissions problem, and research into alternative fuels is limited for now, it appears inevitable that some economic instruments of the kind proposed by the DNR will be imposed. The airlines complain that few of these instruments are accompanied by environmental justification or a regulatory impact analysis. They also fear that the introduction of, say, a fuel tax in some countries and not in others would unfairly affect competition.

Many airlines are already investing substantial amounts of money in being seen to be "environmentally friendly" - Lufthansa has invested some DM300 million ($180 million) in the last five years on environmental issues, not counting the money spent on buying cleaner, more efficient new aircraft. Some airlines, including British Airways and Lufthansa, produce annual environment reports.

Cynically, this could be seen as an attempt to hold off the introduction of the new economic penalties the green pressure groups are pushing for. It is nevertheless clear, however, that the larger and wealthier airlines, at least, are taking the issue seriously.

Source: Flight International