Warming effect of contrails more than half the total climate impact of aircraft

Aircraft contrails have a significant impact on global warming, and understanding them better could help reduce aviation’s impact on climate.

Edward Gryspeerdt, Research Fellow and lecturer, at the Grantham Institute explains – the greenhouse gases (GHGs) created by flying are significant, but the contrail clouds formed by planes have a significant impact too.  

What do Clouds have to do with Climate Change?

Clouds have a significant impact on the climate, with some reducing global warming while others increase it. The composition of clouds is influenced by aerosol particles.

Satellite image of contrails to the south of France, from NASA Worldview.

Edward Gryspeerdt: Essentially, all clouds are reflective and create a cooling effect on the climate, but some are also very good at trapping heat, acting as a blanket across the planet and helping to warm it further. So some clouds decrease global warming, while others increase it.  

Clouds are made from lots of droplets of water and maybe a few crystals of ice – each of these forms around an aerosol particle, such as sea salt, desert dust, soot from burning fossil fuels, and sulfuric acid.

If you increase particles, you get more droplets or ice crystals in that cloud, and that changes its properties.  

How are Aviation and Shipping linked to Clouds?

Shipping and aviation produce particulates that impact clouds and climate. Aircraft contrails, formed by burning jet fuel, can trigger cloud formation.

Jet fuel burning creates water and soot particles, if the conditions are right, they freeze when leaving the engine – small ice crystals from that grow and spread as clouds.

How do these Clouds Impact the Climate?

Edward Gryspeerdt: In a nutshell, ships change existing clouds, making them cool the Earth further, while clouds created by planes warm the Earth. 

Ships produce a lot of aerosols but typically emit them low in the atmosphere – this changes clouds near to the Earth’s surface, making them brighter and creating a cooling effect.  

Clouds formed from aviation are high up (10km up in the troposphere), and are very cold, making them good at stopping heat leaving the Earth and keeping it warm. 

So by producing more of these high-level clouds, aircraft are warming the climate through more than just their greenhouse gas emissions. 

How Significant is the Warming Effect of Clouds from Aviation?

Airplane contrails have a significant impact on climate change. The warming effect of contrails is more than half the total climate impact of aircraft. In fact, their warming effect is greater than all CO2 emissions from flights since the beginning of aviation.

This doesn’t sound good – What Can We Do?

Ideally, we’d reduce flying and all its associated emissions. However, there are benefits to society from flying and such drastic changes are possibly unrealistic right now.

Better understanding contrails can help reduce their impact on the environment. Redirecting planes, using different aircraft or fuel, and flying at different heights are some ways to reduce their warming effect.

Are the Contrails or Greenhouse Gases from Aircraft Worse for the Climate?

Reducing aircraft emissions involves a trade-off since greenhouse gases (GHGs) emitted by planes linger in the atmosphere for hundreds of years. Thus, rerouting a flight to avoid a warming contrail does not eliminate the carbon dioxide (CO2) and warming resulting from the additional fuel burned. Therefore, it is crucial to assess the potential benefits before implementing any changes.

Watch more timelapse videos of clouds, on Dr Gryspeerdt’s blog.

Are You Optimistic We Will Solve Climate Change?

In some ways I am optimistic because we actually know what the solution is, but it’s the doing bit that is difficult – we just need to get on and do it.

We have to work out how to do it in a way that is effective and quick. This is challenging, but there are still pathways that will see us avoid dangerous climate change. 

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