Making planes fly higher than normal could slash climate impact by 60%

Making planes fly higher than normal could slash climate impact by 60%

By Joe Pinkstone For Mailonline

Published: 13:00 GMT, 12 February 2020  | Updated: 13:15 GMT, 12 February 2020

Forcing a tiny percentage of flights to change their cruising altitude by 2,000ft could slash the climate impact of plane contrails by almost 60 per cent, a study reveals.

Aircraft contrails - the white streams that billow out behind planes and criss-cross the sky - can form clouds which are just as harmful to the environment as carbon dioxide emissions.

The vast majority of these troublesome plane-induced clouds are caused by just 2.2 per cent of flights.

Researchers found that making 1.7 per cent of aircraft fly 2,000 feet higher or lower than planned could drastically reduce the formation of contrails and these clouds.

The impact of this is a reduction in contrail warming by 59.3 per cent with only a 0.014 per cent increase in fuel consumption and CO2 emissions, the study found

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Corresponding author Dr Marc Stettler, a civil engineer at Imperial College London, said: 'This demonstrates the potential to reduce aviation's climate forcing immediately.'

Contrails are formed when pieces of unburnt carbon from plane fuel are thrown out of the engine and become surrounded with water vapour which condenses on them.

In certain conditions where the air is supersaturated with ice particles, these trails can spread.

They then mix with cirrus clouds and form unique 'contrail cirrus' clouds that can last for 18hours.

These clouds are the issue which account for much of air travel's warming impact.

The study, published in the journal Environmental Science & Technology, used a model to calculate black carbon emissions for specific aircraft engine types and power.

This was combined with data on the characteristics and climate impact of contrails from individual flights and detailed weather information.

The authors of the study suggest flying at either lower or higher altitudes to avoid prime areas for contrail cirrus cloud formation.

However this is also fraught with issues as diversions from a standard flight plan can lead to increased CO2 emissions.

Previous studies that considered lateral diversions indicated this could offset any reduction in contrails.

But by targeting the few flights that cause the most warming contrails the small changes outweighed the CO2 penalty.

Dr Stettler said: 'Although this study is restricted to the Japanese airspace, the qualitative findings are likely valid for other mid-latitude regions.'

In the long term, if conventional engines were also replaced with cleaner-burning engines, overall contrail impact could be reduced by 91.8 per cent, say the researchers.

Clouds can have both a cooling and warming effect. They reflect some of the sun's rays back into space, but also block some of the heat radiated by Earth's surface.

Dr Stettler said: 'During the day, contrails can cause a cooling effect by reflecting incoming shortwave solar radiation back to space, while trapping and re-emitting longwave infrared radiation back to the Earth's surface at all times.'

But on average, research has shown both thin natural cirrus clouds and contrails have a net warming effect.

Dr Stettler said: 'The climate forcing of contrails and induced-cirrus cloudiness is thought to be comparable to the cumulative impacts of aviation CO2 emissions.

'Contrail models are vital in validating the effectiveness of different mitigation solutions such as the use of alternative fuels, new engine technology and flight diversion strategies.'

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