Do contrails add water to the atmosphere over time?

[Lisa P]

Long contrails are quite rare where I live (South East Qld Australia) we get more short persistent ones as planes are either ascending or descending through an area that obviously has more humidity but certainly not a daily or even weekly occurrence. I try to imagine the planes are like spray bottles spraying all this water into the upper troposphere. I wonder exactly how much extra water is up there compared to 10, 20, 30 years ago and the effect on climate & cloud cover.

 

[Trailblazer]

TLong contrails are quite rare where I live (South East Qld Australia) we get more short persistent ones as planes are either ascending or descending through an area that obviously has more humidity but certainly not a daily or even weekly occurrence. I try to imagine the planes are like spray bottles spraying all this water into the upper troposphere. I wonder exactly how much extra water is up there compared to 10, 20, 30 years ago and the effect on climate & cloud cover.

It's important to remember that almost all of the water in long contrails like that is water that was already in the atmosphere, and is condensing/freezing onto the exhaust trail. It's like when you get a cold beer out of the fridge and put it outside on a humid day, you get water condensing onto the bottle and running down the sides. It's not "new" water, just water that has been made visible.

In the case of planes, of course there is some new water produced from burning the fuel, but it is only a tiny part (it has been estimated as one part in 30,000 in the case of a persistent trail).

Having said that, with 2 billion barrels of jet fuel being burnt every year, that's still a lot of water being produced around the world. But compared to the massive amount of water vapour already up there I think it's pretty insignificant. I haven't done the maths though!

 

[Lisa P]

It's important to remember that almost all of the water in long contrails like that is water that was already in the atmosphere, and is condensing/freezing onto the exhaust trail. It's like when you get a cold beer out of the fridge and put it outside on a humid day, you get water condensing onto the bottle and running down the sides. It's not "new" water, just water that has been made visible.

In the case of planes, of course there is some new water produced from burning the fuel, but it is only a tiny part (it has been estimated as one part in 30,000 in the case of a persistent trail).

Having said that, with 2 billion barrels of jet fuel being burnt every year, that's still a lot of water being produced around the world. But compared to the massive amount of water vapour already up there I think it's pretty insignificant. I haven't done the maths though!

Thanks Trailblazer, that's why I check here often to make sure I don't go off on a tangent! I think I need a more indepth study of how contrails form and I know just the place to go for that! The problem I have is words don't mean much to me I have to translate them to pictures in my mind so your cold beer analogy is great for me. I can read all about contrails but it doesn't sink in, show me pictures and hey presto.

 

[Lisa P]

ohh and seems like I am not the only one with this problem, there is soooo much bunk out there...

 

[deirdre]

ohh and seems like I am not the only one with this problem, there is soooo much bunk out there...

also, contrails are clouds. I'm thinking that it doesnt matter where the water comes from because the atmosphere can only hold so much water (ie saturation level) then it condenses into clouds and eventually falls (as rain, snow etc).

I'm thinking... when the atmosphere (air) is dry, more water evaporates from lakes and rivers etc. When the atmosphere is already wet, less water evaporates.

I've never been to Australia, so dont know what your weather is like, but in Connecticut we have "humid days" ie. the air is wet. The reason hot humid days can be dangerous is that our sweat cant evaporate off our bodies as easily. Evaporating sweat is our primary (i think primary..but important) way of "cooling down".

so i think the air (saturation level) takes care of water content itself.

 

[Trailblazer]

I found this study which suggests that the water vapour content of the atmosphere is increasing, but that increase is due to the warming of the atmosphere. Warmer air can hold more water vapour.

https://www-pls.llnl.gov/?url=science_and_technology-earth_sciences-moisture

"When you heat the planet, you increase the ability of the atmosphere to hold moisture," said Benjamin Santer, lead author from Lawrence Livermore National Laboratory's Program for Climate Modeling and Intercomparison. "The atmosphere's water vapor content has increased by about 0.41 kilograms per square meter (kg/m²) per decade since 1988, and natural variability in climate just can't explain this moisture change. The most plausible explanation is that it's due to the human-caused increase in greenhouse gases."

Kilograms per square metre seems like a rather strange unit, but I suppose it removes the effect of varying pressure (and therefore weight per unit volume) as you go higher into the air. So presumably this refers to the mass of water vapour in the atmosphere above each square metre of the Earth's surface.

The surface area of the Earth is about 509 million square kilometres, or 5.09 x 1014​ square metres.

So the total water vapour content has increased by 0.41 x 5.09 x 1014​ = 2.09 x 1014​ kg.

Taking the annual usage of jet fuel as 2 billion barrels, with one barrel being 42 gallons and one gallon weighing 6.8lb (or 3.08kg), the amount of fuel burnt in a decade is 10 x 2,000,000,000 x 42 x 3.08 = 2,587,200,000,000 kg, or 2.59 x 1012​ kg.

Each kilogram of jet fuel produces 1.37 kg of water when burnt, so the total "new" water from that jet fuel is

1.37 x 2.59 x 1012​ = 3.54 x 1012​ kg.


Dividing that by the increase in water vapour content we get:

3.54 x 1012​ / 5.09 x 1014​ = 0.017.

So jet fuel consumption in one decade has produced about 1.7% as much water as the increase in water vapour content due to warming.

Actually I was surprised it was as high as that.


Edit to add:

From this paper, the average total mass of water vapour in the atmosphere as a whole is 1.27 x 1016​ kg. The annual contribution from jet fuel combustion (3.54 x 1011​ per year, calculated above) is about 0.0028% of this amount.

http://acd.ucar.edu/~lsmith/massERA40JC.pdf

 

[skephu]

I think the more relevant question is whether contrails add/generate more water in the form of ice to/in the atmosphere. And the answer is yes. Also known as "aviation-induced cloudiness".

 

[Jay Reynolds]

There is a water cycle and water that is in the air is constantly being run through the cycle. There is also a global balance which TB explained. The cycle is part of a system which is regulated by the sun, oceans and land mass.

So, just because water is released by burning stuff doesn't mean it just stays in the sky, it enters into a contantly variable cycle. The urine a Wildebeest once deposited on the plains of the Serengeti might have ended up in your cup of tea after being lifted up to the heavens and rained down into the aquifer of a mountain spring.....get the point?

 

[Pete Tar]

Is there anything that could change the amount of water the atmosphere can hold, ie its saturation point, so we end up with a dense venus-like atmosphere but no precipitation?
I imagine that would involve some pretty significant changes in orbit and mass and atmospheric pressure, so any concern we might end up with an over-saturated atmosphere is much too theoretical to be a real worry.

 

[Trailspotter]

The urine a Wildebeest once deposited on the plains of the Serengeti might have ended up in your cup of tea after being lifted up to the heavens and rained down into the aquifer of a mountain spring...

Enriched with aluminium?…

 

[Trailblazer]

There is a water cycle and water that is in the air is constantly being run through the cycle. There is also a global balance which TB explained. The cycle is part of a system which is regulated by the sun, oceans and land mass.

So, just because water is released by burning stuff doesn't mean it just stays in the sky, it enters into a contantly variable cycle. The urine a Wildebeest once deposited on the plains of the Serengeti might have ended up in your cup of tea after being lifted up to the heavens and rained down into the aquifer of a mountain spring.....get the point?

Agreed. I didn't mean to imply that the water produced by aircraft just hangs around in the atmosphere.

 

[MikeC]

Back to the original question, the answer is no, contrails do not add to atmospheric water.

Exhaust does - and it does so whether it forms a contrail or not, and it does so regardless of the type of engine or hydrocarbon fuel used - all engines burning hydrocarbons "make" water, whether internal or external combustion, piston or turbine or rotary or whatever......

Also hydrogen fuel creates water when combusted.

 

[JFDee]

Is there anything that could change the amount of water the atmosphere can hold, ie its saturation point

Global warming is expected to raise the absolute amount of water in the atmosphere.

Not sure if you can compare Venusian sulfuric acid clouds with water clouds, but virgas (evaporating rain) are not uncommon on this planet either.