Are rainfall and contrails connected?

05 May 2020

PLANE-WITH-CONTRAIL

A plane flying across the sky, leaving a streaky contrail cloud behind it

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Question

Forum user Syphrum sent us in this question: I live on a major air route and am used to seeing the sky covered in contrails but at the moment it is strangely clear. We are experiencing a very dry spring with scarcely a spot of rain all month and none promised until May. Is there any correlation?

Answer

Climate scientist Ella Gilbert answered this one for us...

As you say, it has been unusually dry and mild in the UK in recent weeks. After a warm January and the wettest February on record, March temperatures were distinctly average, although drier and sunnier than usual.

However, the Met Office has announced that April 2020 is provisionally thought to have been the sunniest we've ever seen since records of total sunshine hours began in 1929. This was particularly true in the southeast, so for instance: Cambridge got 64% more sunshine than is usual for April. However, this lovely weather was actually a result of persistent high pressure systems over the UK, which typically do find settled conditions. Very frustrating for everyone stuck in doors of course.

You're right to point out a link between contrails and climate though. A study in the journal Science suggests that contrail cirrus has warmed the planet more than all the CO2 emitted since commercial aviation began. The line-shaped cirrus clouds that form behind an aircraft are responsible for warming the atmosphere, especially at the altitudes and latitudes where air traffic is most concentrated such as Europe or North America.

Although their effects on surface temperatures and precipitation is still unclear, one study published in the leading journal Nature suggests that contrail cirrus reduces natural cloudiness, which may impact temperatures and precipitation on the surface.

So although there is a link between contrails and climate, the reduction in air traffic is likely not responsible for bringing the lovely weather we've been having and if anything would probably be expected to have the opposite effect.

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