Large potential exists to reduce aviation's climate impact through minor changes in flight trajectories, finds study
Dr Sigrun Matthes, who led the REACT4C project, and Dr Volker Grewe with the Stuttgart Airport award
Wed 8 Oct 2014 – With only small changes to flight routings and altitudes on North Atlantic air traffic, climate impact reductions of up to 25% can be achieved by only a small increase – less than 0.5% – in economic costs, finds a study conducted by participants in a major European research project. Scientists from environmental, meteorological and aerospace research institutions investigated transatlantic air traffic for one specific winter day and using powerful modelling tools analysed routing changes required to achieve reductions in CO2 emissions and non-CO2 climate impacts from air traffic. The study was conducted as part of the REACT4C EU-funded project that concluded in April. The project’s leader, the German Aerospace Center (DLR), was recently presented with the Aviation Award for environmentally friendly air travel by Stuttgart Airport Company.
The study evaluated a set of around 800 eastbound and westbound flights between Europe and North America on the day in question – when there was a strong jet stream – and analysed which routing changes were required to achieve a reduction in the climate impact from those flights. As well as CO2 emissions, this included non-CO2 effects such as chemical changes of ozone and methane caused by emissions of NOx, water vapour and contrail-cirrus formation. The climate impact of non-CO2 emissions depends on the time and position of aircraft as atmospheric processes leading to climate change vary with background conditions and transport pathways within the atmosphere.
Except for CO2, which has a long perturbation lifetime, the impact of a locally confined air traffic emission shows a large spatial and temporal variability. In some regions, emitted NOx is rapidly ‘washed out’, whereas in others it remains for several weeks in the atmosphere. Formation of persistent contrails occurs in ice-supersaturated regions, and also has a large spatial and temporal variability. The study investigated lateral and vertical re-routing options to avoid such climate sensitive regions using a state-of-the-art climate-chemistry model and a Eurocontrol air traffic simulation tool.
Although the study of weather specific re-routing of air traffic to minimise climate impact has been undertaken before, none had included such a broad range of atmospheric effects and traffic complexity as addressed in this study, says the paper published in the September edition of the journal Atmospheric Environment.
The one-day evaluation was used to calculate five-dimensional climate cost functions comprising emission location (3D), time (1D) and type of emission (1D), which define the climate effect of a locally confined emission. Climate cost functions allow for the determination of the climate impact of a kilogram of CO2, NOx or water vapour, or a kilometre of contrail from flying through a region at a particular time. The size of these regions was set by the climate model used to make the calculations, which splits the world up into 100 x 100km areas, called gridboxes.
These calculations allow transatlantic flights to be designed in a more environmentally-friendly manner through altered flight routes and altitudes, and also in relation to additional costs. “In an application to one specific weather situation, this method could reduce the effect on the climate by 25% whilst only raising the costs by 0.5% for flights going westwards,” explained Dr Volker Grewe of DLR’s Institute of Atmospheric Physics, lead author of the study.
Added Dr Emma Irvine of Reading University’s Department of Meteorology, who was part of the project team: “It’s important to note that our study is very specific to the North Atlantic region – I would not necessarily expect these results to directly apply to flights in other regions, since the climate impact of the non-CO2 emissions is very dependent on location, altitude and weather situation.”
The study has been expanded since the paper was written to cover the range of weather situations that are typical for the North Atlantic. “What we find overall is that it is possible to achieve substantial reductions in climate impact through air traffic management. The potential for reducing the climate impact depends a lot on the weather situation, but also on what level of cost increase is acceptable, since this method would require some flights to take longer routes or fly at non-optimal flight altitudes,” said Irvine.
“It’s also interesting to note that the potential for reducing the climate impact depends on what direction you are flying in. We found that it is possible to achieve larger reductions in climate impact for a smaller cost increase for westbound flights – which are flying against the wind. This is because re-routing eastbound flights out of the favourable tailwinds in the jet stream can incur a large fuel penalty.”
For the one winter day, the researchers found a reduction of the climate impact of up to 60% for westbound and 35% for eastbound traffic could be achieved with an increase of 10-15% in economic costs due to extra fuel burn and crew time. The driving parameter is the reduction of the climate warming by contrails, notes the paper.
“By making only small changes to the flight paths and altitudes of some flights we could reduce the overall climate impact of transatlantic air traffic on that day by 25%, relative to flying flight routes with the minimum cost,” said Irvine. “This does increase the overall operating cost on this day, but by less than 0.5%.”
She said that although the REACT4C project had finished, the results were still being analysed before a final write-up. Funding permitting, there is a requirement for further research into climate-optimal flights, she added.
The REACT4C (Reducing Emissions from Aviation by Changing Trajectories for the benefit of Climate) project had eight participants from six European countries. As well as DLR and the University of Reading, the partners included Eurocontrol, Airbus, the UK Met Office, the Center for International Climate and Environment Research (CICERO) in Oslo and Manchester Metropolitan University.
Stuttgart Airport Company’s (FSG) inaugural Aviation Award ‘for environmentally friendly air travel’, which also carries prize money of €75,000 ($95,000), was presented to Dr Grewe and DLR for the study by Germany’s Minister of Transport and Infrastructure, Winfried Hermann, at a recent ceremony.
After a worldwide call, 11 jury members from the scientific, industrial and political sector selected three winners from 31 entries from Europe, North America and Asia. Another DLR project to reduce noise at airports through satellite navigation won second prize and the third prize went to the University of Stuttgart's Institute of Aircraft Design for the design of a six-seater, electric-driven airplane for the General Aviation sector.
“The aviation industry consistently strives to reduce the effect it has on the environment. As a provider of infrastructure on the ground, Stuttgart Airport acknowledges its responsibility to contribute towards these efforts,” said FSG Managing Director Prof. Georg Fundel. “The Aviation Award is a new step in shaping a more efficient and sustainable future for air travel.”
Added Walter Schoefer, also Managing Director at FSG: “The Aviation Award is an element of our ‘fairport STR’ concept. We aim to become one of the highest performing and most sustainable airports in Europe. We are therefore promoting ideas for new technologies and concepts that can make air travel more sustainable and economically efficient.”