Decarbonising aviation is vital for climate action as a rising non-Western middle class starts to fly — COP28 has raised this ambition: Robert J. Miller

Robert J. Miller is Chair in Aerothermal Technology at Cambridge University. Speaking from COP28 in Dubai to Srijana Mitra Das, he discusses new directions in the effort to develop environment-friendly aviation:

Q. What are you working on at the COP28?
A . I have been invited to King Charles’ Sustainabl e Markets Initiative and the Business and Philanthropy Climate Forum hosted by the COP28 Presidency. This brings together heads of state with CEOs to drive meaningful climate action. I was asked to co-chair the aviation roundtable which had stakeholders like the International Civil Aviation Organization, Rolls Royce, financiers like Bank of America, etc. This aimed to raise ambition in decarbonisation by achieving flight with no carbon impact.

Q. How significant is the aviation sector in the climate crisis?
A. Aviation directly contributes 2% to 3% to total greenhouse gas emissions. But it also has non-CO2 effects — when a plane flies at a certain altitude, it sometimes leaves a persistent contrail, the cloudy line at its back. At times, this forms clouds and traps heat to Earth which can raise the effect to 6%. Now, in 2018, only 11% of the world flew. But a rising middle class across Asia, South America and Africa will be flying soon — that 2% or 6% sum will increase.

Q. What innovations are you working on as possible solutions to this?
A. I am Director of the Whittle Laboratory in Cambridge which is one of the world’s leading aerospace labs, named after Frank Whittle, a Cambridge alumnus who invented the jet engine in 1937. We are looking both at technologies which will decarbonise aerospace and doing modelling of the entire sector to understand how to act. There are three broad technological directions here — the first is fuels to replace jet fuel. These are termed ‘sustainable aviation fuel’ (SAF) and take carbon in the atmosphere or biomass. This replacement is relatively easy to do since the planes or the infrastructure won’t change much. However, to make these fuels would take about 40% of global electricity — that would rise to 80% by 2050. The second strategy is using hydrogen to power new advanced jet engines running on liquid hydrogen. However, you need to completely redesign planes and infrastructure here. Hydrogen is about a third lower in electricity requirements than replacing fuels though. The third technology is to use battery electric aircraft, replacing the jet engine with an electric motor and running it from battery. This requires even less energy — but as the batteries are heavy, the aircraft are unlikely to go further than 500 kilometres.

Q. When could these be applied?
A. We’ve been working with the Aviation Impact Accelerator team to study the system and understand implementation. It’s hard to predict when a sector undergoes disruption. So, we’ve developed four 2030 Sustainable Aviation Goals which can shorten the time to achieve climateneutral aviation by 2050. Firstly, these goals include design to ensure SAF are truly sustainable. Virgin just flew the world’s first 100% SAF transatlantic flight. But to make these fuels, the quantity of biomass and hydrogen required to scale is immense — if not properly regulated, the aviation industry will steal these scarce resources off other sectors. So, the first goal is to have global policy in place by 2030 that requires us to consider the total impact of these fuels on climate and nature. The second is driving a new business model — currently, the aviation sector has been reducing fuel burn to fly one passenger by 1 km by about 1% a year. We believe by establishing incentives and regulations, we could drive a 40% drop in fuel use. The third goal is to accelerate demonstrations of key technologies needed for long-haul hydrogen aircraft. Hydrogen fuel, stored in liquid form at -253 centigrade in a heavy tank, is still lighter than jet fuel. It has real advantages for longdistance flight. We need to demonstrate these technologies by 2030. The last of the goals is ‘Operation Blue Sky’ or removing the clouds formed by aviation. Around one in 30 flights produces a region of clouds that traps heat into Earth like a blanket — the clouds formed by one in 30 aircraft thus warm the planet as much as all the other planes’ CO2 does for 100 years. But you can avoid this by changing the altitude of the plane in flight when you go through an ice supersaturated region where clouds form. The goal is to trial and deploy a contrail avoidance system by 2030.

Q. How do these innovations stand in terms of pricing?
A. This is difficult to estimate but costs will rise — making these fuels and the energy involved require large investments. In an average flight, the fuel is about a third of the cost. If we switch to a SAF made with renewable energy, the cost could be three to eight times — that could make a ticket price even double. However, there are people around the world just about to take their first flight — the contact which flight gives us is a human good and we must ensure these remain accessible. Having said that, I think we could fly less in the West.

Views expressed are personal