Authors of study into future trends in aviation noise and emissions respond to "suppression" claim
Fri 16 May 2008 – The Aviation Environment Federation (AEF), a UK NGO, recently publicized a “shock” report it had obtained – which the AEF said had been “suppressed” – that forecasted a “huge increase” in the future environmental impact of aviation. The claim has received widespread media attention. Two leading co-authors of the paper, Gregg Fleming and David Lee, have provided their side of the story to GreenAir.
The paper in question, ‘Trends in Global Noise and Emissions from Commercial Aviation for 2000 through 2025’ (link below), was co-authored by researchers from the Department of Transportation Volpe Center (US), Wyle Laboratories (US), EUROCONTROL (EU), QinetiQ (UK) and Manchester Metropolitan University (UK). It assessed the future impacts of aviation-related noise and also local air quality and GHG emissions. The AEF said the paper had been prepared for a US-Europe ATM R&D seminar held last year in Barcelona but the organizers had turned it down (see story).
Gregg Fleming, Chief of the Environmental Measurement and Modeling Division,US Department of Transportation Volpe Center:
The authors were of course disappointed the paper was not accepted to the FAA/EUROCONTROL conference. But the reality is that this does not constitute “suppression”. Only about one-third of the papers submitted get selected for inclusion at this particular conference. Further, there was a poster on display with the results of the analysis.
This report is part of the ongoing work we participate in on the Committee on Aviation Environmental Protection (CAEP) of the International Civil Aviation Organization (ICAO) to assess its environmental goals. The paper is contained in ICAO’s Environmental Report 2007 (link below), which has been accessible since last summer via the ICAO website. Anyone in the world could have downloaded and read it.
Missing from AEF’s description of the study is any mention of the key assumptions that underpin the assessment results:
1.This trends assessment does not include assumptions about improvements in future aircraft technology. This stands in sharp contrast to projected trends as well as the commitment of the airline industry to at least a 20% fuel efficiency improvement by 2020.
2.The analysis makes the assumption that airport capacity provides no limitation to growth, clearly not realistic given such constraints at a variety of airports in both the US and Europe.
3.This analysis assumed no improvements in future CNS/ATM technology, despite the endeavours and clear forecasts in both the US and European plans for gains in this area.
Hence, it is easy to see that this trends assessment should be considered an upper level – not a likely forecast – of future noise and emissions trends.
We are currently halfway through our next CAEP work programme. As part of the programme, we are planning to update the future trends taking into account technology and operational improvements. None of the aviation forecasts to date – at least those I’m aware of – consider renewable fuels, and this may also play an important role in the future.
Professor David Lee, Director, Centre for Air Transport and the Environment (CATE), Manchester Metropolitan University (MMU):
The furore is quite amusing but there is also a serious point about potential future emissions.
The work was originally presented at the ICAO CAEP7 meeting in February 2007 by Gregg Fleming. This is essentially a closed meeting.
The point of the work was to use the very limited number of sophisticated global emissions inventory models that exist (four in total, MMU’s being one of them) to project global aviation emissions to 2025, using the ICAO-CAEP traffic forecast (‘Forecast and Economic Analysis Support Group (FESG) forecast’). The approach adopted was a ‘technology freeze’, i.e. to keep the aircraft modelled at current day levels of technology for simplicity and comparative purposes, since there is not a unique solution to implementing technological improvements in these models. Thus, there is some inherent over-estimation of emissions. However, since it uses the FESG fleet forecast, which evolves the fleet to larger aircraft, there IS an element of technology development in there.
Currently, technology is widely quoted to deliver improvements of 1-2% per year. However, this is in the realms of urban myth, since such improvements in fuel efficiency are originally based upon a seminal piece of work by David Greene, a transportation and energy analyst of Oak Ridge National Laboratory (US) published in 1992. Few, it seems, have actually read his work when they repeatedly cite this improvement rate. Fuel efficiency improvement rates come from four sources only: technology (engine/airframe), aircraft size, load factor and operational improvements (routings, CDAs, etc.). What is being widely misrepresented is a fuel efficiency gain of 1-2% per year from technology (alone), since Greene’s improvements estimate was derived from an analysis that included assumptions of an increasing load factor, the introduction of new types of aircraft entering the fleet, including blended wing body aircraft and large open-rotor fan aircraft (neither of which have actually entered the fleet), plus a shift to larger aircraft.
The simple fact is that we don’t actually know what the fuel efficiency improvement rate is, globally, or the main influencing factors on it. This is something that our research centre at MMU (CATE) is currently working on in one of our research projects (which will be ready later in 2008).
Does our study contain startling news? Well, yes and no. When it was originally presented at the CAEP7 meeting in February 2007, it was rather dismissed as being implausible by some of the CAEP national members and Observers since their attention was focused on the technology freeze assumption. However, I recall that it was a test of models, and not intended to be a specific ‘realistic’ forecast. Because of the technology freeze assumption, there was a reaction from part of the floor of the meeting that the numbers must therefore be questionable (I represented the UK as a technical advisor to the UK CAEP Member’s team, and am engaged in the CAEP work programmes). However, this reaction was unjustified and did not reflect an appreciation of current and prior work on emissions projections, nor was there an appreciation of how the global fleet and technology pass-through develops.
The key point for me is what level of CO2 emissions we may expect by 2025.
The said paper has an inherent overestimation BUT this is not large. The development and introduction of new technologies to market is slow, production lifetimes are long and the consequential roll-over of the global fleet is therefore also rather slow (around 25 years). The Intergovernmental Panel on Climate Change’s special report ‘Aviation and the Global Atmosphere’ (IPCC, 1999, link below) predicted emissions of around 1 Gt CO2 in 2015. The downturns following 9/11 and SARS maybe cost 1-2 years of growth but the overall increase in revenue passenger kilometres between 2000 and 2005 was 22%, with global emissions of CO2 from aviation increasing by 8.4% over this period (ICAO and IEA statistics, respectively). Our own recent work for the Quantify European project (link below), once again using the FESG fleet forecast and including reasonable assumptions over technology development, indicates emissions in 2020 of around 1.06 billion tonnes CO2.
So, 1.2 to 1.4 billion tonnes of CO2 by 2025 is not outlandish. It all, of course, depends on growth and the economy. Clearly, historically, growth has outstripped fuel efficiency improvement rates and is expected to continue outstripping them in the future. This was stated in the IPCC 1999 report and clearly re-stated in the IPCC Fourth Assessment report (WGIII, Chapter 5 summary, link below).
