The projected abatement potential in CO2 emissions due to
reductions in fuel burn can be complemented through enhanced
use of alternative fuels. As Hileman and Stratton (in this issue)
suggest, in addition to environmental issues and climate change in
particular, the interest in alternative fuels was driven by oil import
dependence and the strong rise in oil price from year 2000.
Compared to surface transport modes, only fuels with a high
energy content per unit weight and volume can be used in
aviation, in order to compromise a minimum of its payload
capability. In addition, over at least the short-to-medium term,
the long lifetime of aircraft mandates the use of “drop-in” fuels,
i.e., fuels with characteristics similar to petroleum-derived jet fuels
that do not require any infrastructure changes. Based on a lifecycle
well-to-wake analysis, the authors find a high variability with
respect to greenhouse gas emissions of second-generation biofuels
mainly with respect to the type of land-use changes underlying
the cultivation of the respective crops. Among these biofuels,
switchgrass-based Fischer–Tropsch jet fuels promise to release
close to zero greenhouse gas emissions, especially if no land-use
changes are involved in their cultivation.
Finally, advances in air traffic management represent a further
degree of freedom for mitigating CO2 emissions. Reynolds (in this
issue) discusses the potential causes of flight inefficiency and
develops flight inefficiency metrics to quantify the performance
of various geographic air transport systems. Based on two metrics,
lateral inefficiency (extra flown ground distance) and fuel ineffi-
ciency (extra fuel burned compared to the minimum), he quantifies inefficiencies in different flight phases to indicate where the
largest potential scope exists for improving the system. He highlights the relative importance of allowing aircraft to fly closer to
their optimal four-dimensional trajectories and reducing ineffi-
ciencies in high fuel burn phases of flight, i.e., during take-off and
climb, and discusses the operational and technical enablers that
might be appropriate to help achieve improvements
Any of the emissions reductions described above will lead to
changes in the price of air travel. Because of the interaction of major
variables of the air transportation system, a change in prices will
impact air transport demand and supply characteristics. Thus, Dray
et al. (in this issue) apply an integrated model to explore the impact of
a global carbon tax on aviation fuel. In this application, the carbon tax
is used to subsidize the purchase of new aircraft within either the
global air transportation system or within that of the developing
world to subsidize the early retirement of aircraft older than 20 years
of age. As the authors show, such schemes can lead to a reduction of
global, year-2050 lifecycle passenger aviation-related CO2 emissions
by around one-third related to a no-policy case. Of this emission
reduction, only about one-third is due to fleet replacement and thus
increased use of new technologies. The remaining two-thirds are a
consequence of the rising carbon price and split equally between
demand reduction and a projected increase in use of biofuels. If the
policy only funds fleet replacement in the developing world, global
emissions can be reduced by around one-quarter. Although the cost of
reducing lifecycle CO2 emissions is around 40–80 US$/tCO2 in the first
case, and around 20–50 US$/tCO2 in the regional application, and thus
above those associated with an all-sector global carbon tax to achieve
similar levels of reduction, the acceptance within industry may be
higher because they are the key beneficiaries.
Aircraft noise can have significant physical and monetary
impacts on people residing near airports. With the demand for
commercial aviation projected to rise at an annual rate of around
5% over at least the next two decades, policymakers and aircraft
manufacturers are particularly interested in understanding these
impacts to evaluate technological, operational, and policy changes
that can help to accommodate the forecasted growth while
keeping detrimental effects to citizens and to the environment at
a manageable level. Current practices for assessing the monetary
impacts of aviation noise typically use hedonic pricing methods
that estimate noise-induced property value depreciation.
However, this approach requires detailed knowledge of local
housing markets, which is not readily available at a fine resolution
for most airport regions around the world. Therefore, He et al. (in
this issue) propose a new noise monetization method based on
city-level personal income, which is often more widely available.
Using a meta-analysis of 63 hedonic pricing studies from eight
countries, conducted between 1970 and 2010, they estimate a
model that explains the willingness to pay for noise abatement