This part of the Earth’s atmosphere is nearly all
the time colder than À40
C, often it is with about
À70
C the coldest one in mid-latitudes in the
lowest at least 60 km. Therefore, the water vapor
concentration in these layers must be lower by
typically 3–4 orders of magnitude than at the
Earth’s surface in low- and mid-latitudes. Hence,
several emissions of an aircraft besides carbon
dioxide, for example unavoidable water vapor, in
principle avoidable nitrogen oxides can lead to a
considerable disturbance of the radiation budget
of the planet. First, via the formation of rather
persistent condensation trails, an ice cloud, during
frequently favorable meteorological conditions,
and second, via the formation of ozone around
cruising altitudes because of the nitrogen oxide
emissions.
In addition, the growth rate of commercial air
traffic was on average above the one for the global
gross economic product, leading to a growing
relative contribution of air traffic to the changed
composition of the atmosphere. Only very
recently did the growth rate no longer surmount
the growth rate of world economy as strong as
before.
However, it was only in the late 1980s when
first publications dealt with air traffic’s potential
influence on climate. Earlier, in the early 1970s,
the planned supersonic aircraft fleet in the USA
had led to an assessment of the impact of such
aircraft on the stratospheric ozone layer. At this
time the consequences of the emission of the trace
gas nitrogen dioxide (NO 2 ) were the main reasons
for the investigations, because it is strongly
involved in stratospheric ozone chemistry leading
to ozone depletion at altitudes above about 20 km
but to ozone increases in the troposphere and
lowest stratosphere.
In 1996, the steadily growing public and scientific discussions on air traffic and its potential
effect on global climate have stimulated the International Civil Aviation Organization (ICAO), the
UN specialized agency that has global responsibility for the establishment of standards,
recommended practices, and guidance on various
aspects of international civil aviation, including
environmental protection, to ask the Intergovernmental Panel on Climate Change (IPCC) to assess
in a special report [17] entitled “Aviation and the
Global Atmosphere” the air traffic influence on
global climate. In this report not only the effects of
air traffic on atmospheric composition and on
climate were assessed but also projected into the
future using air traffic growth scenarios. These
results and new findings have entered the third
and fourth full IPCC assessments [19–21];
hence, the hitherto known facts have been presented to the political arena and have led to first
hesitating measures to reduce emissions, like the
European Union’s decision in 2009 to include air
traffic into the European emissions trading
scheme, to become effective on January 1, 2012.
This entry will start with the greenhouse gas
emission history of air traffic in section “Emissions
of Climatically Relevant Substances by Aviation,”
influenced both by the above average growth rate
of this economic sector but also by the strong
increase in fuel use efficiency per passenger kilometer, which has been stronger than for road traffic
and much stronger than for railways. This section
will also include projections of future air traffic
greenhouse gas emissions using estimates from
scenarios of IPCC. It continues with the knowledge
about long-lasting contrails and their dependence
on favorable meteorological conditions in section
“Aviation-Induced Cloudiness.” This section will
also include cirrus clouds formed or transformed
because of air traffic, existing besides the easily
detectable linear contrails. Section “Changes of Air
Chemistry by Air Traffic” is then devoted to
changes in air chemistry caused by air traffic emissions. Section “Transport Sector’s Contribution to
Future Climate Change” extrapolates into the
twenty-first century with known scenarios of
human behavior. It follows the section on “Why
did International Air Traffic So Long Escape an
Emissions Trading Scheme?” The first attempt of
the European Union to include international air
traffic into an emissions trading scheme will be
described in section “The European Directive to
Include Air Traffic into the Emission Trading
Scheme.” The second last section on “An Airline
Emission Index” will present essentials of an airline index that includes a ranking concerning carbon dioxide and nitrogen oxides emissions,
published very recently. The last section will
328
Aviation and Atmosphere
the time colder than À40
C, often it is with about
À70
C the coldest one in mid-latitudes in the
lowest at least 60 km. Therefore, the water vapor
concentration in these layers must be lower by
typically 3–4 orders of magnitude than at the
Earth’s surface in low- and mid-latitudes. Hence,
several emissions of an aircraft besides carbon
dioxide, for example unavoidable water vapor, in
principle avoidable nitrogen oxides can lead to a
considerable disturbance of the radiation budget
of the planet. First, via the formation of rather
persistent condensation trails, an ice cloud, during
frequently favorable meteorological conditions,
and second, via the formation of ozone around
cruising altitudes because of the nitrogen oxide
emissions.
In addition, the growth rate of commercial air
traffic was on average above the one for the global
gross economic product, leading to a growing
relative contribution of air traffic to the changed
composition of the atmosphere. Only very
recently did the growth rate no longer surmount
the growth rate of world economy as strong as
before.
However, it was only in the late 1980s when
first publications dealt with air traffic’s potential
influence on climate. Earlier, in the early 1970s,
the planned supersonic aircraft fleet in the USA
had led to an assessment of the impact of such
aircraft on the stratospheric ozone layer. At this
time the consequences of the emission of the trace
gas nitrogen dioxide (NO 2 ) were the main reasons
for the investigations, because it is strongly
involved in stratospheric ozone chemistry leading
to ozone depletion at altitudes above about 20 km
but to ozone increases in the troposphere and
lowest stratosphere.
In 1996, the steadily growing public and scientific discussions on air traffic and its potential
effect on global climate have stimulated the International Civil Aviation Organization (ICAO), the
UN specialized agency that has global responsibility for the establishment of standards,
recommended practices, and guidance on various
aspects of international civil aviation, including
environmental protection, to ask the Intergovernmental Panel on Climate Change (IPCC) to assess
in a special report [17] entitled “Aviation and the
Global Atmosphere” the air traffic influence on
global climate. In this report not only the effects of
air traffic on atmospheric composition and on
climate were assessed but also projected into the
future using air traffic growth scenarios. These
results and new findings have entered the third
and fourth full IPCC assessments [19–21];
hence, the hitherto known facts have been presented to the political arena and have led to first
hesitating measures to reduce emissions, like the
European Union’s decision in 2009 to include air
traffic into the European emissions trading
scheme, to become effective on January 1, 2012.
This entry will start with the greenhouse gas
emission history of air traffic in section “Emissions
of Climatically Relevant Substances by Aviation,”
influenced both by the above average growth rate
of this economic sector but also by the strong
increase in fuel use efficiency per passenger kilometer, which has been stronger than for road traffic
and much stronger than for railways. This section
will also include projections of future air traffic
greenhouse gas emissions using estimates from
scenarios of IPCC. It continues with the knowledge
about long-lasting contrails and their dependence
on favorable meteorological conditions in section
“Aviation-Induced Cloudiness.” This section will
also include cirrus clouds formed or transformed
because of air traffic, existing besides the easily
detectable linear contrails. Section “Changes of Air
Chemistry by Air Traffic” is then devoted to
changes in air chemistry caused by air traffic emissions. Section “Transport Sector’s Contribution to
Future Climate Change” extrapolates into the
twenty-first century with known scenarios of
human behavior. It follows the section on “Why
did International Air Traffic So Long Escape an
Emissions Trading Scheme?” The first attempt of
the European Union to include international air
traffic into an emissions trading scheme will be
described in section “The European Directive to
Include Air Traffic into the Emission Trading
Scheme.” The second last section on “An Airline
Emission Index” will present essentials of an airline index that includes a ranking concerning carbon dioxide and nitrogen oxides emissions,
published very recently. The last section will
328
Aviation and Atmosphere