The environmental NGOs welcome the publication of the Intergovernmental Panel on Climate Change's (IPCC) Special Report on "Aviation and the Global Atmosphere". While the Special Report contains a Summary for Policymakers (SPM), the paper at hand has been produced to (i) make policy-makers aware of the concerns of the environmental NGOs about aspects of the Special Report; (ii) draw policy-makers’ attention to several policy areas which received only limited discussion in the SPM; and (iii) highlight its most significant conclusions as viewed by the environmental NGOs.

I) Concerns by the environmental NGOs

The environmental NGOs are concerned that the Summary for Policy Makers does not fully reflect the discussion in Chapter 10 of the Report on the potential use of regulatory and market-based mitigation measures. The decision-makers need to be aware that it is no longer a question of whether mitigation measures are required to limit emissions from aircraft, but how such a strategy should be developed and implemented.

Attention is also drawn to the assumptions used in the reference scenario that the average traffic growth per year between 1990 and 2050 is expected to be 3.1%, while the average annual growth rate for fuel burn over the same period is forecast to be only 1.7%. While there will always be a high degree of uncertainty associated with any forecasts over such a long time frame, growth rates since 1990 have generally been well in excess of these figures.

As a result of operational improvements, the industry expects fuel efficiency to be improved by 8 to 18%, largely through the introduction of measures such as CNS/ATM. It is important to note that all scenarios represented in this report take into account full implementation of CNS/ATM. Thus any further improvements will only approach the predictions but will not have any additional benefit. In addition, the Report does not address the issue of "rebound", which is the extra growth in demand that these improvements may stimulate. Chapter 8 of the report acknowledges that fuel-efficiency improvements may attract more traffic due to the cost savings accruing to airlines which may be reflected in lower air fares.

It is clearly stated in the Report that technological improvements will not be sufficient to offset the demand. It is therefore important to consider innovative and creative ways in which the demand can be tackled. Thus, policies will need to be developed that put the emphasis on the avoidance of unnecessary travel, such as the use of telecommunications instead of physical travelling.

Although some uncertainties still exist, the scientific facts provided in the report should prompt decision-makers to act based on the "precautionary principle", which is the starting point for any environmental action. The trade-offs between different environmental impacts are highlighted in the report, which conveys the idea that actions initiated to reduce some environmental impacts would create other, more acute problems somewhere else. The erroneous impression is created that aircraft emissions could have positive effects or could compensate for other environmental problems.

Three important factors call the need for precautionary action:

Although the basic scenario considered in this report is making business as usual assumptions, its predictions are very weak in terms of the growth rate of aviation and the implementation of the Kyoto Protocol is not taken into account when considering the comparison with other global warming effects (Annex shows that if one takes into account the Kyoto Protocol, given its rapid growth, the share of aviation emissions will be much higher than the one considered in the report). Policy-makers need to apply the precautionary principle based on a higher growth scenario than the basic scenario.

II) Issues that received only limited attention in the Summary for Policy Makers

In our view, the mitigation options constitute one of the most relevant parts of the report. However, they received only limited attention in the summary addressed to policy makers (SPM). Instead, the further research needed and the uncertainties linked to the research are overemphasised.

Our approach for this section will be to first highlight the most important outcomes in the report. Then, we would like to add some additional points, that are contained in the body of the report but not in the SPM.

The IPCC Report considers various operational and policy measures aimed at reducing emissions from aviation. Based on information supplied by the industry, the Report takes account of the likely effects of improvements in fuel-efficiency, the development of low-emission technology, and improved operational procedures (largely relating to the introduction of air traffic management improvements). The following types of measures are envisaged to improve the fuel efficiency:

  1. Technological improvements

The industry forecasts that changes to engine and airframe designs will result in a further 40 to 50% improvement in fuel efficiency by 2050. Further reductions in NOx emissions are also predicted. The IPCC Report considered that alternative fuels to kerosene were unlikely to be in commercial use within the time-scale covered by the study;

  1. Operational improvements

The report estimates that further reductions in fuel burn could be made in the region of 8 to 18%, largely through the direct routing opportunities available through the introduction of CNS/ATM. Higher load factors, and optimising aircraft speed were also considered;

However, the most significant finding of the report is that:

Technological and operational efficiency improvements alone will not be sufficient to fully offset the effects of increasing emissions.

It is clear that other measures are therefore needed. The report refers to: 1) market-based options such as environmental levies (taxes and charges) and emissions trading (the use of "cap and trade" mechanisms); 2) policies and regulations, including more stringent engine emission certification standards, and the removal of subsidies and incentives to the industry which have negative environmental consequences, including modal shift; and 3) voluntary agreements with the industry and research programmes.


1) Market based options

The Report considers that levies on fuel and en route charges are the most environmentally effective levies.

Their effect would be a reduction in the consumption of aviation fuel by reducing the growth in demand for air transport.

The report concludes from an OECD study that, based on historical trends, the rate of energy intensity reduction in civil aviation was very responsive to fuel prices. Hence, a meaningful increase in fuel price could increase the rate of energy intensity reduction". Furthermore, the OECD shows that "cumulative fuel levies resulting from an increase in the price of aviation fuel of up to 5% per year could result in at least a 30% reduction in aviation energy use in 2020 relative to the reference scenario". ICAO concluded that "any resulting cost increases passed on to consumers would result in a reduction in emissions" (primarily through lower traffic demand). It also warned that any price increases not passed on to consumers would reduce airline profitability.

The Centre for Energy Conservation and Environmental Technology study found that raising the price of fuel (with the addition of an environmental charge equal to 125% of its cost) would half the predicted growth in aviation emissions in Europe. The study also found that an emissions charge in European airspace would have little impact on competition between domestic and non-European carriers.

Emissions trading would allow all industries to co-operatively minimise the costs of reducing emissions. However, for an emissions trading system to be efficient, it is necessary to have a cap on emissions and rules for trading reductions under such a cap.

2) Policies and regulation

Deregulation and removal of subsidies are important because they give producers and consumers the appropriate signals about pollution costs and natural resource scarcities. Governments support the aviation industry implicitly by not making it pay for its environmental cost; there are also other indirect or hidden subsidies such as non-market pricing for infrastructure services, below-market financing, tax and depreciation preferences for oil, and direct government ownership

  1. As part of a package of measures, voluntary agreements and research could be used and would allow to set environmental targets.

The measures mentioned above can limit growth of aircraft emissions by encouraging technological innovation, effecting greater operating efficiencies in the aviation industry, and by affecting demand.

In addition, the report states that it is important to consider the precautionary and "polluter pays" principles set out in the 1992 Rio Declaration as relevant to the economic analysis of policies for limiting the growth of aviation emissions.


III) The main conclusions of the report, as viewed by NGOs

1) The contribution of aviation to global warming

Addressing the overall climate effects of aircraft, the most significant conclusions of the IPCC Special Report are:

b) The Scientific Assessment

Aircraft emissions which have an impact on the upper atmosphere (most subsonic and supersonic aircraft operate in the upper troposphere and the stratosphere at altitudes ranging between 9km to 20km) are: Carbon dioxide (CO2); Water vapour (H2O); Nitrous oxides (NOx); Sulphur oxides (SOx) and Soot particles.

The contribution that each of the above emissions makes to climate change is expressed in terms of "radiative forcing". This represents the change to the energy balance of the Earth's atmosphere (expressed in watts per square meter) and is based on a global and annual average.

Aviation contributed approximately 2% of all carbon dioxide emissions from human sources in 1992, and its implications for climate change are well recognised. The report points out that the other greenhouse gas (GHG) emissions from aircraft are also important. NOx emissions from subsonic aircraft react to increase ozone in the upper troposphere and lower stratosphere. Increased ozone concentrations increase global warming. NOx emissions also react to decrease levels of methane present in the atmosphere, which is said to have a cooling effect on the Earth's surface. However, the IPCC Report notes that while the climatic effects of changes in ozone and methane resulting from aircraft NOx emissions are "of similar magnitude and opposite in sign, the latitudinal structure of the forcing is different so that the net regional radiative effects do not cancel".

Aircraft are also responsible for increased concentrations of water vapour in the lower stratosphere, that plays a large part in the formation of contrails. The Report estimates that contrails covered about 0.1% of the Earth's surface in 1992. This is greatest over the United States, the North Atlantic and Europe. 0.2% increase in global cirrus cover since the start of the ‘jet age’ has been observed, but much uncertainty still remains. Although their impact is relatively small compared to other aircraft emissions, sulphates and soot tend to cool or warm the Earth's surface respectively, and are also important in the formation of clouds.

The IPCC Report points to one further effect of subsonic aircraft emissions to decrease UV radiation. On the other hand, decreases in stratospheric ozone from a second generation of supersonic aircraft would increase UV radiation. Taken together, the combined fleet would still increase the erythemal dose rate (a measure of how effective UV irradiance is in causing sunburn).

T.Johnson / AEF / JULY1999

B. Schell, T. Sledsens / T&E / 27-28.07.99


Annex: Radiative Forcing from aviation in 1992, 2050 and the precentage (2050 relative to 1992), T. Sledsens / T&E / 28.07.99

Source: IPCC, Aviation and the global atmosphere, p. 187 and table 6.2



TOTAL RADIATIVE FORCING 1992 (in 10-3 /m2)



2050 relative to 1992

Carbon dioxide (CO2)

direct ->

+ 18

+ 74

410 %

Nitrous oxides (NOx)


reduces methane (CH4)

- 14

- 45

320 %


produces Ozone (O3)

+ 23


260 %

Water vapour (H2O)

direct ->

+ 2

+ 4

200 %


see contrails








see cirrus







Sulphur oxides (SOx)

direct ->





see contrails








see cirrus







Soot particles

direct ->





see contrails








see cirrus










+ 20

+ 100

500 %



(+0 to +40)

(+0 to +160)






+ 50

which represents 3.5 % to human produced global warming

+ 190 (range 130 to 280)

which represent a high percentage of the contribution to global warming (EDF: 400 to 600)

380% (260-560 %)

(EDF: 800-1200%)

*) The percentage of aviation emissions in the total greenhouse emissions in 2050 is directly linked to the implementation of the KYOTO targets. If other sectors reduce their emissions and the aviation sector does not, then the contribution from aviation will be a lot higher than the highest scenario in the Report.