The implications of intermediate stop operations on aviation emissions and climate

Abstract

Among the
various transport modes aviation’s impact on climate change deserves special
attention. Due to typical flight altitudes in the upper troposphere and above,
the effect of aircraft engine emissions like e.g. water vapour, nitrogen oxides
and aerosols on radiative forcing agents is substantial. The projected doubling
of aircraft movements in the next 15 years will lead to an increase of
aviation’s impact on climate and requires immediate mitigation options. Besides
technological measures also new operational strategies are widely discussed;
one of these concepts which has been subject of several studies in the past is
Intermediate Stop Operations (ISO). It is based on the idea to reduce the stage
length of flights by performing one or more intermediate landings during a
mission. Here, we analyse the ISO concept by combining different models, which
include a realistic traffic simulation taking into account operational
constraints and ambient conditions, like e.g. wind, the calculation of engine
emissions and the integration of a climate response model.We analyse the ISO
concept for today’s worldwide aircraft fleet, including its influence on global
emissions distributions as well as the impact on climate change by taking into
account CO2 and non-CO2 effects, arising from contrail-cirrus, water vapour and
nitrogen oxide emissions. We show in agreement with earlier findings that due
to shorter flight distances the amount of fuel burnt over the mission can be
reduced by roughly 5% on average globally. For the first time, we quantify the
climate impact of ISO, where the flight trajectory is optimised for fuel use
and the aircraft is not redesigned for the ISO procedure. We find an increased
warming effect, which arises from nitrogen oxide and water vapour emissions,
which are released at higher cruise altitudes and which over-compensate reduced
warming effects from CO2 and contrail-cirrus. However, we expect a climate
impact reduction for ISO even with existing aircraft, avoiding the higher
flight altitude in the first flight segment and hence reducing the fuel
savings. Thus, climate impact benefits could be achieved if lower fuel savings
were acceptable. Moreover, this negative climate impact is found for the
particular case of introducing ISO using the current wide-body fleet. It does
not necessarily apply to the adoption of ISO using aircraft redesigned for a
shorter range.