1. Aviation impacts on climate: Where are we heading?
Kristian J. Walker (Physical Geography BSc) and Ling Lim (Research Fellow)
Figure 2: Aviation and background CO2 concentrations from various forecasts including the observed concentrations.
Introduction
The aim of the project was to review widely‐used aviation scenarios and assess the accuracy of earlier
forecasts to reported levels of aviation emissions. For example, the IPCC Special Report on Aviation (IPCC,
1999) provided forecasts from the base year of 1992 to ‘future’ years 2015 and 2050. We are now at a point
in time, where we can compare ‘old forecasts’ to reported traffic activities. This project also gave us the
opportunity to identify where aviation emissions is heading. Therefore, we can determine not only the
forecast accuracy, but also the likely growth trajectory of aviation emissions.
Aviation fuel burn
Generating forecasts for the aviation sector is a challenging task, since the industry can be heavily influenced
by unpredictable world events such as war, disease outbreak or economic crisis. An extensive literature
review was conducted to obtain fuel burn data for various aviation scenarios. The data collected spanned the
years 1970 to 2100. However, only two scenarios reached 2100, and thus, Table 1 demonstrates a snapshot of
this extensive collection of data up to 2050.
Table 1: Selected global civil, military and total fuel burn for various inventories/scenarios. n.a. = not available
Aviation carbon dioxide (CO2) emissions
A selection of aviation scenarios and their associated fuel burn were linearly interpolated between available
data years, in order to obtain yearly fuel burn. These scenarios were:
• NASA, CAEP‐4/FESG with data for 1992, 2015 and 2050 (IPCC, 1999)
• CONSAVE with data for 2000, 2020 and 2050 (Berghof et al., 2005)
• QUANTIFY with data for 2000, 2020 and 2050 (Owen et al., 2010)
• GIACC with data for 2006, 2012, 2016, 2020, 2025, 2026, 2036 and 2050 (ICAO, no date)
• Lee et al. (2013) with data for 2006 to 2050.
CO2 emissions for these datasets were calculated using a fuel to emissions conversion factor of 3150 g CO2
per kg fuel. The resulting CO2 emissions are illustrated in Figure 1. These aviation emissions were compared
with those derived from the International Energy Agency (IEA) kerosene (IEA, 2014) (aviation fuel) sale data
and the same fuel to emissions conversion factor as in the scenarios. These aviation trends were also
compared with the various background scenarios for all anthropogenic sources, as shown in Figure 1. The
background scenarios were obtained from various publications that contributed to the IPCC reports:
• RCP: RCP8.5 (Riahi et al., 2011), RCP3PD (van Vuuren et al., 2011)
• SRES: A1F1, B2 (IPCC, 2000)
• IS92: IS92e, IS92c (Leggett et al., 1992)
• WRE: WRE750, WRE350 (Wigley et al., 1996).
Figure 1: Aviation and background CO2 emissions from various forecasts including the IEA fuel (kerosene) sales data. The
wedge of the scenario denotes the upper and lower ranges of the forecasts, with the upper/lower scenarios noted in
brackets.
Aviation CO2 concentration
In order to calculate aviation CO2 concentrations (Figure 2), the aviation emissions scenarios from Figure 1
and the historical aviation CO2 emissions derived from IEA fuel sales data were used as input in a simple
climate model, LinClim. Historical background CO2 concentrations from Meinshausen et al. (2011) and future
projections from RCP (2000‐2100), SRES (1970‐2100), IS92 (1995‐2100) and WRE (1991‐2100) are compared
with the aviation concentrations in Figure 2. It shows that aviation's contribution to background CO2 increases
with time. It can also be seen from the figure that the rate of increase in aviation CO2 concentrations is
greater than that of the background concentrations.
Aviation CO2 temperature response
In order to account for the non‐linearity effects of aviation CO2 concentrations on temperature, it was
necessary to calculate the difference between background concentrations, and background without aviation
concentrations. Therefore, the aviation scenarios are coupled to the relevant background (for example, Lee et
al., 2013 with RCP background). As for the climate parameters, those that reproduce the transient behaviour
of the ECHAM4 General Circulation Model were used. The results from these LinClim simulations are
demonstrated in Figure 3.
Figure 3: Aviation and background CO2 temperature response for a variety of forecasts.
Dissemination
The output from this work has been presented as a poster at the 4th International Conference on Transport,
Atmosphere and Climate in Germany. This will also be written‐up for the conference proceedings and special
issue peer‐reviewed journal, Meteorologische Zeitschrift. In addition, the results will be presented to the
International Civil Aviation Organization (ICAO)’s working groups and included in the Centre for Aviation,
Transport and the Environment (CATE)’s research report for the UK Department for Transport (DfT).
What next?
This placement has provided the opportunity to put skills learnt during university into practice. As such, the
Research, Enterprise and Innovation (REI) Summer Vacation Studentship has put into motion, my progression
into the aviation sector and research. I plan on utilising this learning experience to apply skills developed
during the studentship at a postgraduate level, whilst studying the MSc in Sustainable Aviation.
This work also forms part of a wider high profile research at MMU, which is conducted on behalf of the DfT,
to assess and mitigate the climate impacts from aviation. The results from this study would be used to inform
policy makers on whether mitigation efforts are likely to meet the targets set out back in the 1990s or
whether more stringent legislations/policies are required to achieve them.
References
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2050 Final Technical Report. DLR, Köln, Germany.
• ICAO (no date): GIACC/4: IP/1, IP/2, IP/3. [Online] [Accessed on 15 June 2015]
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• IEA (2014): Oil Information 2012. International Energy Agency, Paris.
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Acknowledgements
Kristian Walker is funded by the MMU Research, Enterprise & Innovation Summer Vacation Studentship and
Ling Lim is funded by the UK Department for Transport.
Centre for Aviation, Transport and the Environment (CATE)
School of Science & the Environment
Manchester Metropolitan University, United Kingdom