Science Questions

Do aircraft contrails negate global warming?

Sun, 28th Mar 2010

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Question

Neil S. Briscoe asked:

Hi

 

Just listened to your last Sunday's broadcast and heard at the end that you're talking about planes vapour (or con) trails as cloud formers.

 

Some time ago, I heard on one of the World Service's broadcasts that, thanks to the 9/11 attacks (when they grounded all flights) people were able to work out that con trails during daylight hours were actually an assistance to prohibiting global warming whereas con trails during the hours of darkness were an aggrovator of same.

 

I hope you are going to be able to confirm, or otherwise, what I've previously heard.

 

Many thanks.

 

Regards

Neil

Answer

We put this to Dr Jim Haywood, from the Met Office:

Ben -   Does it matter whether itís day or night?

Jim -   Yes, it does indeed.  Itís exactly what that question is about.  Really, weíre talking about a cooling, if you like from the reflection of sunlight and a warming during the night time which can cause a reduction in whatís called the diurnal temperature range.  After 9/11, there was certainly evidence of a reduction in the diurnal temperature range from a particular study.  But itís quite difficult to disentangle that signal, if you like from the natural meteorological events that can occur.  And when they looked at it in a little bit more detail, it became almost impossible to distinguish from other events that had nothing to do with 9/11.  You still could see this signal in the diurnal temperature range, just due to the natural variability of the atmospheric system.

Ben -   So it may have an impact that we can't see because itís no bigger than noise.

Jim -   Itís just difficult to detect.  Thatís right.

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Neil S. Briscoe asked the Naked Scientists: Hi Just listened to your last Sunday's broadcast and heard at the end that you're talking about planes' vapour (or con) trails as cloud formers. Some time ago, I heard on one of the World Service's broadcasts that, thanks to the 9/11 attacks (when they grounded all flights) people were able to work out that con trails during daylight hours were actually an assistance to prohibiting global warming whereas con trails during the hours of darkness were an aggrovator of same. I hope you are going to be able to confirm, or otherwise, what I've previously heard. Many thanks. Regards Neil What do you think? Neil S. Briscoe , Thu, 25th Mar 2010

First of all, think you need to shift your thinking from the idea/concept of 'global warming' to that of global climate change, for while some regions may get warmer others will almost certainly get a lot colder, and the very important bottom line is that no one knows what will actually happen.

Having said that, I do recall hearing about research that seemed to reveal that the absence of jet aircraft contrails was noticeable.  However, that is not to say that the absence or presence of jet contrails makes any significant difference to the global climate; it is just just that the difference was detectable.

The bottom line, I suspect, is that when compared with the natural variation in cloud cover due to the much larger scale 'normal' weather systems, the presence or absence of jet aircraft contrails is likely to be negligible because even though they may act as 'seeds' for areas of cloud formation larger than just that of the contrail itself, these will still be tiny in comparison to the already extant weather formations. LeeE, Fri, 26th Mar 2010

I can assure you that we will have a global warming no matter how many aircrafts we put up :) When white, some of the sunlight do get reflected by the ice crystals inside the clouds but when dark ::)) forget it, well not really there's still ice reflecting but the clouds will magazine more heat the darker they become. It's called Albedo

"Different types of clouds have different albedo values, theoretically ranging from a minimum of near 0 to a maximum approaching 0.8. 'On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth.'"

Furthermore, the aircraft will accumulate to more CO2 as it burn up its fuel exchanging it for thrust. And that fuel comes from under the earth adding to the pollution we have. But I do love aircrafts :) So let's take care of the cars first, shall we?

yor_on, Sat, 27th Mar 2010

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