The Roadmap to True Zero: Targeting not only CO2 but aviation's total environmental impact
Mon 28 Sept 2020 – Through the COVID crisis, it has been extremely heartening to see the aviation and aerospace sectors continue to focus on and, in some cases, redouble their commitment to decarbonisation, writes Nikhil Sachdeva of global strategy consulting firm Roland Berger. While decarbonisation is essential and must remain a priority, carbon dioxide (CO2) is not the only greenhouse gas released by aviation which contributes to global warming. There are many other pollutants and effects, from NOx to particulates, contrail cirrus and aviation induced cloudiness. Unfortunately, the non-carbon effects are less clearly understood than carbon and remain much more difficult to quantify. In effective radiative forcing terms, latest research suggests total impact of approximately three times that of carbon alone. In global warming potential terms, this ranges between two to four times, depending on the timeframe considered. Significant error bars complicate the issue further.
However, while scientific uncertainty remains over the exact quantum of non-CO2 effects, the practical reality is quite clear: both CO2 and non-CO2 effects contribute to warming and are extremely important to mitigate. For aviation to remove its total environmental footprint, the industry must work to tackle both carbon and non-carbon effects with equal emphasis and aim for a ‘True Zero’. If this holistic picture is not taken into account in making critical decisions in the coming few years, we may face the issue of having decarbonised, only to realise that we missed – or possibly exacerbated – the impact of non-carbon effects.
Despite the scale of the problem, there is unfortunately no ‘silver bullet’ or single solution which can conceivably address the whole challenge and achieve True Zero, while retaining and maintaining a functioning aviation ecosystem.
1 Assuming SAF pathways and engine designs which allow 100% drop-in 2 Hybrid solutions also compatible with SAFs, which would reduce net carbon impact 3 Aviation induced cloudiness 4 For a narrowbody scale aircraft
Three categories of solutions exist: novel sustainable aviation fuels (SAFs) such as Power-to-Liquid eKerosene, aircraft electrical propulsion and hydrogen propulsion. While SAFs are a net-zero carbon solution, they do not sufficiently address other radiative forces. While parallel and series hybrids are a step in the right direction on all effects, only battery electric can completely remove them in operation but is technologically and commercially extremely difficult to deliver for large commercial aircraft. Hydrogen options are also indeed very promising but do not sufficiently address all warming effects: hydrogen fuel cells are a nearly True Zero solution but still produce large quantities of water vapour and potentially contrails, while hydrogen combustion, though technologically somewhat less complex, would also still produce NOx.
So how can aviation completely remove its environmental impact? We at Roland Berger propose the Roadmap to True Zero: a 5-step plan to minimise aviation’s annual environmental footprint by 2050.
First, airlines must continue on their existing path to keep improving their operations and keep switching to the latest aircraft. Second, we need continued investment into smoother air traffic control – but also, crucially, an investment into trajectory optimisation, which is essentially air traffic control for contrail minimisation. Third, the aerospace sector must invest heavily in not one but three categories of aircraft technology, broken down by flight mission requirement: battery-electric aircraft for the shortest flight segments, SAFs powering the longest flights performed by the largest aircraft, and hybrid-electric and/or hydrogen propulsion serving the all-important narrowbody segment. Fourth, and in parallel, the sector must keep investing in research to continuously improve climate science so we can keep refining our understanding of the problem and a strategy for the solution. Finally, for whatever emissions are remaining, we recommend compensating for the residual, for example, via rigorous certified offsetting.
The impact of these improvements can be best measured against aviation’s 2050 environmental footprint.
Airline operational improvement measures (such as aircraft weight reduction, best cruise speed adherence and continuous descent) and ATC improvements (such as the Single European Skies initiative) are estimated to be worth an estimated 10% of aviation’s 2050 footprint, driven by a 10% expected reduction in fuel burn.
The impact of replacing aircraft with the latest generation in their category (such as the A320neo, B737 MAX, B787 and A350) is significant. While airlines are currently in dire straits, the aviation sector will hopefully recover strongly in due course, and airlines should endeavour to transition to the best in class aircraft as soon as possible, with an environmental impact reduction worth around 25% by 2050. This relatively high impact is due to the sheer number of very inefficient classic generation aircraft still flying (for example, 35% of the pre-Covid US fleet was classic generation aircraft), and due to the significant reduction in soot and particulates (and thus partial reduction in contrails) afforded by the latest generation of engines.
Next is trajectory optimisation, wherein flights are redirected to minimise contrails, by flying lower and avoiding high risk pockets of air. While this can increase fuel burn slightly, the impact in contrail reduction can be significant, resulting in an estimated 15% reduction in total environmental impact, with no major aircraft or engine technology changes required.
Up to this point in the roadmap, significant impact is already possible – all without the inclusion of new aircraft technologies. However, any further improvement does require revolutionary aircraft platforms.
Battery electric aircraft are applicable to shorter ranges and smaller aircraft, up to 1,500 km, and since they remove fuel burn completely, they eliminate all emissions from the sectors they fly in (assuming batteries are charged with renewable energy), with an impact of around 15%.
In the narrowbody segment, up to 6,000 km, we anticipate bothhybrid and hydrogen aircraft to play equally important roles. Given the scale of the narrowbody market, we expect a bifurcation in aircraft technology with aircraft manufacturers taking on different strategies – we therefore forecast this segment will be addressed by 50% hybrid and 50% hydrogen aircraft. Hybrids will burn not kerosene but SAFs (such as Power-to-Liquid eKerosene), which on a net basis can completely decarbonise. Hydrogen fuel cell aircraft will decarbonise completely in gross emissions but will increase water vapour emissions and not completely remove contrails. In total, the net impact of these aircraft is around 15%.
Finally, for the largest aircraft performing long-haul journeys, the only viable solution expected into 2050 is sustainable aviation fuels. These can decarbonise completely, albeit only on a net basis – with unfortunately minimal improvements in non-CO2 effects. Considering both net CO2 and non-CO2 effects, this is worth 10%.
This leaves approximately 10% of aviation’s total environmental footprint in 2050. This remainder is made up of mainly NOx and contrail effects – and, crucially, we have completely decarbonised. We recommend that the effects of these emissions are compensated in other ways, such as through rigorous and certified offsetting.
Our proposed Roadmap to True Zero is one of many paths that can be considered. Some improvements which are not covered in the roadmap include air traffic concepts such as formation flying, network concepts like replacing long-haul flights with connecting flights, and the impact of new carbon market incentives such as ‘carbon equivalent pricing’. These ideas could indeed be complementary but have not been considered in preference of focusing on technological changes while keeping the network and market structure constant.
In conclusion, we strongly believe that a combination of solutions does exist that can tackle aviation’s CO2 and non-CO2 impacts and pave the way to a genuine True Zero. Today’s focus is on decarbonisation, and while this must remain the priority, non-carbon effects cannot be ignored. However, there is no silver bullet or one-size-fits-all solution. The Roland Berger Roadmap to True Zero thus deploys a mixture of conventional and revolutionary technologies for range-specific missions, including electric, hydrogen and SAFs where they can have the greatest impact, and ‘low hanging fruit’ improvements such as trajectory optimisation. By applying the Roadmap to True Zero, aviation can completely decarbonise by 2050, and its total environmental footprint can be reduced by 90%, with just 10% remaining to be compensated through methods like offsetting to achieve True Zero.
To find out more about the Roadmap to True Zero and to discuss it further, contact the author at email@example.com or connect with Nikhil Sachdeva via LinkedIn. To read the latest analysis in electrical propulsion and other new aviation propulsion technologies, please visit the Roland Berger website, where you can also subscribe for regular updates.
Roland Berger's Roadmap to True Zero presentation at FIA Connect: