Aviation and Climate Change

• Summary
• Situation of Aviation in the 1990‘s
• Climate Impact of Aircraft Emissions
• Outlook
• Measures to Mitigate the Effects of Aviation

Summary

Aviation is the means of mass transport with the worst rating under climate aspects because

• the CO₂-emissions per passenger kilometer are relatively high
• the distances travelled are long because of the high speed of transport
• emissions of aircraft (e.g. contrails, Nitrogen Oxides) have a warming impact which is two to four times higher than that of the CO₂-emissions alone.

To sum it up: there is hardly any other single action with comparable negative climate impacts than taking a plane (if criminal actions and acts of war are excluded).

Furthermore, aviation is the means of transport with highest growth rates on national as well as on international level. Until 2015 a doubling of world demand compared to 1995 is expected, and until 2050 even moderate scenarios show a sixfold increase. In spite of technical progress aviation emissions will grow substantially in the future.

For business-as-usual scenarios, in the middle of the 21st century greenhouse gas emissions from aviation alone would reach the order of magnitude of what human beings altogether can emit without harmfully changing the climate.

Political steps on national and international level have to be taken to prevent this development. Actions should be guided by the polluter-pays principle and the end of subsidies for airlines, airports and airport infrastructure.

Situation of Aviation in the 1990‘s

Aviation is a relatively new means of mass transport but with high growth rates: on average since 1960 global passenger traffic increased 9 percent per year with the consequence that by 1990 passenger transport in planes had reached 2200 billion (2.2 x 10¹²) passenger-kilometers. Aviation then had already achieved a global market share in motorised transport of roughly 10 percent which is growing further. This means the global market share of aviation exceeded rail in passenger transport in the late eighties of the 20^th century.

Furthermore only 7 percent of world population has ever travelled on a plane, so further rise in demand is obvious. In 1995 the demand of air travel within North America alone was more than a quarter of total world demand although North Americans only account for 5 percent of the world population.

Growth rates of air freight are similar to (or higher than) passenger transport. Although the absolute amount (mass) of transported goods is small compared to sea ships and rail, already one third of the value of internationally traded goods is transported in planes.

Climate Impact of Aircraft Emissions

Aircraft emissions are the result of the burning of kerosine. The discussion of this topic can be restricted to kerosine as aviation fuel because it is by far the most important fuel, and there are no alternatives for the coming decades. The emissions have different constituents with impacts on global warming.

The amount of carbon dioxide (CO₂) is completely determined by the amount of kerosine consumed because the energy for the propulsion stems from the burning of carbon. Compared to other modes of transport planes have relatively high specific CO₂ emissions (per passenger per kilometer travelled, also called passenger-kilometer or Pkm). They are in the same order of magnitude as the CO₂-emissions of cars and e.g. in Germany three times higher than those of rail. But this neglects of course that planes are faster than cars. If specific emissions are understood as emissions per time travelled (this is the relevant question for humans because their time is limited, not the distance they can travel) the specific CO₂-emissions of aircraft are five (or twenty) times higher than those of cars (respectively rail) traffic.

But the CO₂-emissions are only between a half and a quarter of the greenhouse gas emissions of aviation. Planes also emit water vapor and Nitrogen Oxides (NO_x) which lead to condensation trails (contrails), methane and ozone formation. The figure below shows the more complicated effects of these emissions on the climate.

Summing up the warming effects of CO₂- and NO_x- emissions and contrails the amount of aviation emissions per time travelled are 10 to 100 times higher than their competitors.

Only 12 civil supersonic aircraft exist today. However, plans for a new generation of supersonic planes appear every year in the media. It should be mentioned that with respect to the emission of greenhouse gases supersonic aircraft are five times worse than subsonic aircraft. Compared to the land based modes of transport the greenhouse gas emissions of supersonic aircraft per time travelled are 100 to 1000 times higher.

But even without supersonic aircraft the emissions of planes are high under the following aspect: If a person flies for one hour in a normal commercial plane he (or she) causes more greenhouse gas emissions than an average person in Bangladesh emits in one year with all he or she does.

In other words: there is hardly any other single action with comparable negative climate impacts than taking a plane (if criminal actions and acts of war are excluded).

Figure: Radiative Forcing from Aircraft in 1992 (which describes the impact of the different aircraft emission constituents to global warming)

Outlook

Until 2015 an average global growth of demand of 5 percent per year is expected. This means that demand will more than double in 15 years. For the time beyond 2015 only scenarios exist with a broad range of possible demand: in the Special Report "Aviation and the Global Atmosphere" (1999) the Intergovernmental Panel on Climate Change (IPCC) sees a plausible demand in aviation from 7800 to 50000 (!) billion passenger kilometers in the year 2050 under the assumption that there are no constraints from airport infrastructure.

This means that in the middle of next century greenhouse gas emissions from aviation alone would reach the order of magnitude of what human beings altogether can emit without harmfully changing the climate.

This is not tolerable. Political intervention is necessary to avoid that such a future comes into life.

Measures to Mitigate the Effects of Aviation

Globalisation of markets, tourism and personal relations are strong driving forces for future growth of aviation. These are also factors which support a peaceful development between countries.

However, the living conditions of future generations especially in countries of the South are threatened if the challenge of climate change is not addressed appropriately. Mitigation measures for aviation are an important part of this response. Political steps on national and international level have to be taken to prevent this development.

The measures should be guided by the polluter pays principle ("the user pays for the effects he causes"). The end of subsidies for airlines, airports and airport infrastructure (also infrastructural subsidies to connect airports to cities) directly result from this.

Also local environmental effects are important. Airports – also if they plan to expand – should respect local air regulation standards as well as reduce their noise emissions especially during the night. To accomplish this airports can introduce airport charges designed on environmental performing of planes.

On the international level, the ICAO (International Civil Aviation Organisation) is the UN body responsible for aviation. Following Art. 2.2 of the Kyoto Protocol to the UN Framework Convention on Climate Change the ICAO "shall pursue limitation and reduction of emissions of greenhouse gases". Since 1998 ICAO is working at moderate pace on this.

The next General Assembly of ICAO in September 2001 has to make decisions to mitigate climate change from aircraft. Otherwise three years are lost because they meet again only in 2004.

The introduction of charges on aviation emissions (at least in industrialised countries) would be an effective measure to accelerate technical progress. There is a study of OECD with the result that a charge with an annual increase of 5 percent would lead at least to a reduction in aviation energy use in 2020 although this would have little impact on demand for air travel.

Finally a ban for (new) supersonic civil aircraft should be adopted due to the troublesome climatic effects of this technology.
 

Manfred Treber
February 2001