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Minor altitude changes could slash aviation emissions

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Changing the altitude of flights by 600 metres could dramatically reduce the climate impact of aircraft, an Imperial College London study has found.

Aircraft contrails could be almost as bad for the environment as the emissions from the aircraft themselves, the researchers said. Contrails include black carbon particles which provide surfaces on which moisture condenses to form ice particles. They can then spread and mix with other contrails to form cirrus clouds that can linger for up to 18 hours producing significant warming effects on the ground below.

This warming impact is due to an effect known as ‘radiative forcing’ which is where the balance is disrupted between radiation coming to earth from the sun and heat emitted from the surface of the earth going out to space, forcing a change in the climate.

Using the Japanese airspace as a model, the researchers found that just two per cent of flights were responsible for 80 per cent of radiative forcing within the airspace. The team simulated these planes to fly 600 metres higher or lower than their actual flight paths and found that the contrail radiative forcing could be cut by 59 per cent by altering the altitudes of just 1.7 per cent of flights.

“A really small proportion of flights are responsible for the vast majority of contrail climate impact, meaning we can focus our attention on them,” said the lead author of the report Dr Marc Stettler.

This, the researchers say, combined with using cleaner aircraft engines, could reduce contrail-caused harm to the climate by up to 90 per cent.

Once of the key differences between the climate impact of CO2 and contrails is that while CO2 will cause atmosphere change for hundreds of years, the impact of contrails is short-lived and the newly proposed measures would have a very quick impact.

Stettler suggests that their method of targeting only the few flights that cause the most climate forcing is the best way to avoid hikes in CO2 emissions. He said: “we’re conscious that any additional CO2 released into the atmosphere will have a climate impact stretching centuries into the future, so we’ve also calculated that if we only target flights that wouldn’t emit extra CO2, we can still achieve a 20 per cent reduction in contrail forcing.”

The study’s first author, Roger Teoh, also of Imperial’s Department of Civil and Environmental Engineering, said: “Our simulation shows that targeting the few flights that cause the most harmful contrails, as well as making only small altitude changes, could significantly reduce the effect of contrails on global warming.”

The researchers say aircraft engines themselves also play a part in how harmful contrails are. Black carbon particles are produced by incomplete fuel combustion, so new, more efficient engine combustion technology could help to reduce them by around 70 per cent.

Earlier this week Airbus unveiled a new design for an aircraft that blends together its wings and body into a shape that should reduce fuel consumption and carbon emissions by 20 per cent.

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