[Tanada]

Everyone accepts that H2O vapor is a global warming gas. In fact it is one of the favorites of those who deny CO2 as a threat to talk about.

The thing is H2O in the troposphere is not a threat, when the air is saturated with humidity and the temperature drops even a little bit the H2O forms droplets and precipitates out of the air back to the surface.

This makes Tropospheric water vapor self regulating. When the H2O rises high enough into the Troposphere it forms clouds. In fact even at the Troposphere it still forms clouds, Cirrus clouds, where droplets slowly accumulate enough size until they fall to a lower altitude level and mix with rain clouds.

That is the Freeze Trap, the boundary layer between the Troposphere and the Stratosphere. Water vapor is common in the Troposphere but rare in the Stratosphere because until mankind came along very little water vapor could get past the trap. A little escapes each year from the few very massive Tropical storms that have updrafts strong enough to pierce the cold trap. A little also gets injected into the Stratosphere when very large volcanic eruptions go off spewing dust, sulfur dioxide, CO2 and H2O up through the cold trap.

Why does it matter? Well H2O is a global warming gas that self regulates in the Troposphere but persists in the Stratosphere. In the Troposphere the temperature drops until you reach the cold trap, where temperatures are so low that water vapor will crystallize on any speck of dust it comes across and form Cirrus clouds. On the other side of the cold trap in the Stratosphere the temperature actually goes up a little bit. Not a huge amount, just enough to keep the H2O from crystallizing on microscopic dust. Water vapor molecules are lighter than air, with a molecular weight of 18 compared to 28 for Nitrogen and 32 for Oxygen. That means once they pass the Cold Trap they are able to keep slowly rising. Eventually they get high enough that they get split into H2 and O fragments and do not reform molecules. Before that happens however they spend decades to millennium, nobody knows how long for certain, as water vapor, the Green House Gas.

Enter Mankind with Technology. Specifically enter high altitude aircraft. Most Jet propelled aircraft fly above 9,000 meters/30,000 feet of altitude. Supersonic aircraft usually can fly a lot higher, between 15,000 meters/50,000 feet and 20,000 meters/65,000 feet. Near the equator this doesn't matter much, the Tropopause, the water vapor cold trap, averages 56,000 feet/17,000 Meters up.
In the temperate zones it averages 43,000 feet/13,000 meters, higher in the summer and lower in the winter. In the sub-polar and polar regions its year average is 30,000 feet/9,000 meters, again higher in summer and lower in winter.

This is the reason why contrails become rarer the further away from the equator you are and the colder the season is. Commercial jets flying passengers from North America to Asia fly the great circle routes whenever possible to save fuel. That mean that traveling from Detroit, Chicago, Saint Louis or anywhere west of there in North America you pass close to or right over the geographic north pole. Most commercial jets fly in the 32,000 feet/9,700 meter to 39,000 feet/11,900 meter altitude band. That means for most of the year all of those commercial flights are flying stratospherically, and some of them do it even in summer. Since the end of the cold war commercial traffic on the polar routes has increased greatly, United Airlines was boasting in 2009 that in less than a decade it had already flown 10,000 times over the north pole. Other airlines with connections between Asia and North America fly those same routes with great frequency as well.

The kicker is, for every gallon of Kerosene aka Jet Fuel burned enough water vapor is released to make 1.2 gallons of water. So for every aircraft mile in the Stratosphere an aircraft like a Boeing 747 burns 5 gallons of Kerosene and releases 6 Gallons of water. Given the vast number of flights now traveling the north polar routes year around and the fact that water vapor released at stratospheric altitudes stays in the stratosphere for very long time periods how do you think this is going to influence the climate?

Stratospheric water vapor content is not something sampled in a lot of places like CO2, however the sampling done by NOAA from New Zealand and Colorado both show water vapor falling from 8 ppm to 2 ppm in the commercial jetliner traffic band in those area's. Stratospheric water vapor near New Zealand gradually falls all the way up to 14,750 meters/48,000 feet, but then it gradually starts increasing again. This is all water vapor trapped in the Stratosphere, and the levels keep rising to 24,000 meters/78,000 feet where the instruments failed to record any further data. The reason the levels start rising above that level is simple physics, water vapor rises unless something condenses it out of the air. The lowest level of the Stratosphere is where commercial jets release water vapor into the air, then it rises naturally to higher altitudes. Not enough jets are adding water vapor to maintain a high level at the bottom of the Stratosphere, but it is trapped and as it rises it adds to the amount already trapped.

[dissident]

We have a good understanding of stratospheric chemistry and transport. Peak values of stratospheric H2O are less than 7 ppmv and occur in the upper stratosphere due to CH4 oxidation (including photolytic breakdown). Without the CH4 source the typical values would be 3 ppmv due to freeze-drying in the "cold trap" around the tropical tropopause where temperatures reach as low as 186 K (in the region around Indonesia where convection is most active).

Massive CH4 emissions can indeed mess up the stratosphere but only if they are ongoing and not short duration events. See below, condensation and sedimentation are still important in the stratosphere. The troposphere is moistened by continuous convective activity. There is no convection in the stratosphere by definition. So only transport through the tropical tropopause or CH4 can feed H2O into the stratosphere.

Tropospheric H2O can only enter the stratosphere through the tropical tropopause due to the structure of the large scale meridional overturning circulation known as the Brewer-Dobson circulation. Also, due to the poleward downward circulation pattern much of the mass entering into the "tropical pipe" (cf work by Alan Plumb at MIT) is flushed below 100 hPa and back into the troposphere. Only a small fraction does the full circuit via the upper stratosphere towards the poles and descending into the troposphere over the polar caps. Any climate simulation for the next 100+ years that I have seen does not show any collapse of the cold trap and massive humidification of the stratosphere. This is because the cold trap will be there for as long as the Brewer-Dobson circulation is active and there is tropical convection. If anything, AGW will intensify tropical convection raising and cooling the tropical cold-point tropopause. There may be some weakening of the Brewer-Dobson circulation for reasons I will not go into that would partly offset the cooling (the BD circulation affects the cold-point tropopause temperature via adiabatic deformation of potential temperature surfaces).

You still have condensation processes in the stratosphere and even if the typical size of condensed particles (ice) is smaller than in the troposphere, the lower density implies that sedimentation rates are more rapid. This fact is also a limiter on the sulfate residence time in the stratosphere which reduces the long term impact of volcanoes and counteracts geoengineering efforts. The transport by the Brewer-Dobson circulation and the removal by sedimentation necessitate SO2 to be injected at or above 30 km (not 20 km as some idiots propose) and around 10 million tons per year. Similarly, you can't load up the stratosphere with as much H2O as you want. We don't have stratospheric snow for simple reason that there is not enough H2O. But we do have enough for the formation of polar stratospheric clouds (which actually fall as they form something we have no experience with the troposphere) in regions where the temperature gets below 196 K. If we had much more H2O in the stratosphere then it would be much easier to condense it.

There was a set of papers produced by researchers at Harvard which considered the role of stratospheric water vapour in warming periods of the past, e.g. the Eocene. Follow the PDF links at this page. Note that the tropical tropopause temperature is always a central issue.

[Tanada]

What kind of a loiter time do you think H2O has in the Stratosphere? Based on email communications I had with Dr. David Archer two years ago I was left with the impression that the majority of it eventually disassociates and the Hydrogen escapes to space. What percentage do you believe eventually falls back into the Troposphere and how long does it take to do so?

[Tanada]

Back in the early 1960's NASA did two massive water injections at 90 to 104 miles altitude to study the effects that would result. You can read about them http://library01.gsfc.nasa.gov/goddardn ... 4_1962.pdf on page three of that pdf, titled Saturn aids GFSC research and the general background on Wikipedia http://en.wikipedia.org/wiki/Project_Highwater ...

The thing is each project released the water as vapor/droplets at very high altitude while trans-polar airline flights are releasing the water vapor as a long constant stream in their exhaust and the altitude is much lower. I don't know if there is any cross over validity to the research but I found it interesting to learn

[sparky]

.
The water cycle is of great interest to me ( Australia is a parched land )

it would not be too wrong to state that water dynamic is the most important component of Earth transfer mechanics
There was some paper on a hydro-static thermostat ( i'll have to search back )
the gist of it ( as I understood it ) was that the evaporation/condensation cycle was a factor for climate stability
and largely self regulating
is it bunkum or is it a solid hypothesis

[dissident]

.
The water cycle is of great interest to me ( Australia is a parched land )

it would not be too wrong to state that water dynamic is the most important component of Earth transfer mechanics
There was some paper on a hydro-static thermostat ( i'll have to search back )
the gist of it ( as I understood it ) was that the evaporation/condensation cycle was a factor for climate stability
and largely self regulating
is it bunkum or is it a solid hypothesis

It is not an either/or. Convective transport of heat from the surface to the tropopause, where the air density is low enough for it to be optically thin to infrared and hence allow the heat to radiate to space, is a strong regulator on surface temperatures in the global average sense. Clearly in the subtropical dry belts you get high temperatures but they are partly offset by advection of colder air from other latitudes. The problem is that such valves do not impose an absolute regime of temperatures on the planet. Even though this pumping of heat intensifies as the troposphere warms it does not fully counteract the warming. (A warmer troposphere means deeper convection and a colder and higher cold point tropopause, which implies more heat loss to space.)

So there are strong regulation mechanisms, with convection being one of the main ones. But convection will not change the fact that the background moisture will increase together with temperature. This moisture is the primary greenhouse "gas" (really vapour). Only some fraction of the extra moisture will condense and precipitate. If somehow precipitation could increase just enough to remove the extra H2O in the troposphere, then there could never be any global warming. Instead, under warming conditions the precipitation gets into a regime of enhanced intermittency and increased deluge event amplitude. This nonlinearity is partly related to the fact that higher air temperatures increase the amount of drying of the soil (you can see the role of the surface on convection in the Amazon rainforest; if the forest is removed the region will become a dry savannah).

[sparky]

.
Thanks for the answers ( tough the "it all depend "sound like pure scientist )
I'm into amateur astronomy and since a decade , we haven't have a decent drought for a while .
our desalination plant remain a white elephant
the cloud cover around Sydney has very noticeably increased.
It led me to believe the albedo must have dropped too .
hence the water, vapor , liquid or solid general interest

P.S. the Amazon ( and South East Asia ) forest cover is going out fast

[Subjectivist]

I saw a blurb the other day about direct flights from Detroit to Beijing and it got me to thinking. During the daylight period in the Arctic, from around March 21 to September 21 there are a lot of flights from North America to Asia.

The air at high altitude over the Arctic is incredibly dry. During the winter months the Tropopause, the layer where the cold trap firms squeezing out the last of the moisture in the air falls to as low as 9,000 meters aka 28,000 feet. It gets so cold at times that the Stratosphere actually can freeze out ice crystals forming noctolucent clouds.

I checked the Delta and United Airlines websites, both give tracking data for their flights. For the flights going over the Arctic Ocean the tracking data reads details until they are around 80 degrees north but once they are a little way north of the coast the data drops out until the approach the Siberian coast on the other side of the ocean. Even so when leaving Canadian airspace they are around 37,000 feet altitude and when data resumes on the other side they are around 39,000-40,000 feet altitude because they are lighter having used up half the fuel they took off with from Detroit/Chicago/NYC.

So all these daily flights over the Actic Ocean dump water vapor high above the cold trap. The water comes out as hot vapor and the relative humidity is so low they do not condense into contrails like they do in the temperate zone further south. Instead they spread out as invisible molecules of H2O vapor that are slightly lighter than the surrounding air molecules. Then as they drift around at these very high dry altitudes they are impacted by infrared light coming from lower layers in the atmosphere. It's not a lot of energy because the Arctic is still very cold but it does give off a little, and H2O is very good at absorbing certain frequencies.

So the question that comes to mind is, warmer molecules in any mixture tend to rise. So how far do these water molecules rise in the constant sunshine north of 80 degrees latitude? Do they make it all the way to the Ozone layer?