Net-zero aviation still contributes to global warming, according to research

Many net-zero aviation projects fail to account for the warming effect of streaks of clouds created by planes, a study has found

Engineering and Technology (E&T) | 26 July 2022

Efforts to make flying greener mostly count carbon dioxide emissions only, an approach that might ignore 90 per cent of future flights' contribution to climate change accounting to new findings.

The research, published in Nature just days after the UK government announced its target of reducing carbon emissions from flights to net zero by 2050, warns that many strategies devised to decarbonise the aviation sector have significant blind spots.

Currently, the only emissions counted by international and most national efforts to decarbonise aviation are those related to the use of jet fuel. In doing so, these standards fail to account for soot, aerosols and water vapour released by aircraft engines.

Nicoletta Brazzola's team at ETH Zurich in Switzerland found that, despite these net-zero strategies, the aviation sector worldwide could increase global average temperatures by between 0.1C and 0.4C, putting at risk the Paris agreement of holding global temperature rises to 1.5C.

"We found the mitigation efforts needed to get aviation to a place where it's compatible with the Paris agreement are enormous," Brazzola said.

The team's modelling has suggested that failing to account for aviation's non-CO2 effects, as most policy-makers are, would ignore 90 per cent of future flights' contribution to climate change. After exploring different future scenarios of demand for flights, the team also analysed how much CO2 would need to be removed from the atmosphere by trees or machines to hit true net zero.

The study showed that, even with only a moderate increase in demand for flights, the status quo of jet fuel and offsetting would require an area the size of Germany to be planted with trees to compensate for the planes' emissions.

"Without a very strong reduction in demand and without very rapid, almost infeasible switches to clean technologies, we would in all cases need to deploy carbon removal to a very large extent," she said, expressing doubts regarding whether carbon-removal projects of that scale would even be feasible.

The conclusions suggested that the aviation sector's landmark short-term plan for reducing its impact on climate change won't be enough. Instead of focusing on carbon-neutral aviation, the researchers have called for a shift in focus in favour of climate-neutral solutions.

Some of the solutions that meet this criterion are hydrogen and battery-powered planes.

"This would be a radical change of direction, but I think it is long overdue," said Paul Williams at Reading University, UK.

Even with all these solutions in place, the study implies that it would be extremely difficult to make the sector truly carbon-neutral within the proposed framework without a significant decrease in the demand for flights.