Could slower flights cut the climate impact of aviation?

Extending flight times by making planes fly slower could reduce emissions from aviation, according to a study from the University of Cambridge.

It suggests that reducing flight speeds by around 15 per cent could decrease fuel burn by 5 to 7 per cent. Planes would likely have to be designed in the future to accommodate this reduction in speed.

The study also notes that the downsides of this policy would fall on passengers – slower speeds could add up to 50 minutes to a transatlantic flight for example.

While just 10 per cent of the world’s population currently flies, aviation already accounts for around 2.5 per cent of global CO2 emissions. If non-CO2 climate impacts are taken into account, its contribution to global warming rises to 4 per cent.

The recommendation is just one part of a report outlining a five-year roadmap from the university that it claims would help the aviation industry achieve net-zero climate impact by 2050.

An ambitious five-year roadmap for sustainable aviation

Current policies, the university’s analysis says, leave the aviation industry seriously off track in meeting its climate pledges. The report sets out what it says are realistic, sustainable goals for the aviation industry which would make reaching net-zero emissions by 2050 more achievable.

“Too often the discussions about how to achieve sustainable aviation lurch between overly optimistic thinking about current industry efforts and doom-laden cataloguing of the sector’s environmental evils,” says Eliot Whittington, executive director at the Cambridge Institute for Sustainability Leadership.

“The Aviation Impact Accelerator modelling has drawn on the best available evidence to show that there are major challenges to be navigated if we’re to achieve net zero flying at scale, but that it is possible.”

The report adds that often these bold measures are overlooked because they require broad changes to the aviation sector which are beyond the control of airlines.

Four recommendations to make sustainable aviation goals achievable

The first goal would be to remove clouds formed by aviation known as contrails. These can act like a blanket in the sky contributing to raised temperatures on the ground. Speeding up the deployment of a global system to avoid these could reduce aviation’s climate impact by up to 40 per cent.

The second would be to implement a new wave of policies unlocking system-wide efficiency gains across the aviation sector. This is where the recommendation to slow down flights comes in alongside replacing planes with newer models and ensuring more aircraft are operating within their optimal range.

Measures like this, the report says, could halve fuel burn by 2050 but would need to tap into efficiency goals that aren’t achievable by individual companies.

The third involves reforming Sustainable Aviation Fuel (SAF) policies to help rapidly scale up production and ensure it is truly sustainable. According to the university’s analysis, the goal is to put in place the global policies required to minimise the wider impact of SAFs on climate and nature.

And the final recommendation is to launch several moonshot technology demonstration programmes to bring forward the timeline for their deployment. The report provides long-haul hydrogen aircraft as an example of this.

Burning hydrogen does not produce CO2 emissions, so it could be utilised to lower the climate impact of flying. The report also says the low weight of this fuel, even with the weight of the tanks included, makes it “advantageous” for long-distance flights.