Vapour Trails and Greenhouse Gas

[Thread Bear]

I was reading an old copy of New Scientist magazine and came across an interesting article...

Aircraft vapour trails are climate scourge

Airlines could boost their emissions of the greenhouse gas carbon dioxide and still halve their impact on global warming. That is the paradoxical conclusion of a new study into the effects of commercial aviation on the environment.


Eliminating contrails offsets extra CO2 from engines.
The CO2 emitted from their engines is not the only way aircraft affect climate. They also do so through their contrails, the long trails of water vapour and ice that form in an aircraft's wake and which can persist for several hours. Contrails trap heat in the atmosphere by reflecting infrared radiation emitted from the Earth's surface.

In 1999 the Intergovernmental Panel on Climate Change (IPCC) calculated that contrails from the world fleet of 12,000 civil airliners contribute as much to global warming as the CO2 their engines pour out as they burn jet fuel.

But global air traffic is growing by around 3.5 per cent per year, and many of those extra flights are long-haul, high-altitude, contrail-forming journeys. So by 2050 contrails will be having a great deal more of an impact on global warming than the CO2 emissions from aircraft engines.


Contrails could be eliminated if aircraft reduced their altitude from about 33,000 feet to between 24,000 feet and 31,000 feet, depending on the weather.

But this would come at a price: lower altitude means denser air and higher air resistance, so planes have to burn more fuel. And this means more CO2 emissions, which would apparently negate any benefits from eliminating contrails.

But according to researchers at Imperial College, London, the idea may work after all. "It seems counterintuitive," admits Robert Noland, one of the authors of the study. But Noland and his colleagues have calculated that if planes flew low enough to leave no contrails behind, their fuel consumption would increase by only four per cent, boosting CO2 emissions by the same amount.


The team based their calculations on a simulation of a year's worth of traffic over the busiest part of Europe, taking into account the need for different aircraft to fly at different altitudes to avoid collisions.

But the proposed trade-off between cumulative CO2 emissions and short-lived contrails should be approached with caution, says Ben Matthews, a climate researcher at the Catholic University of Leuven, in Belgium.

"Such a policy might reduce the warming in the short term in regions where most planes are flying, but still increase the warming in the longer term in southern developing countries," he says.

And the Imperial team admits that reducing altitudes may not be a cure-all, since its burden on air traffic controllers has yet to be fully assessed.

T.B

[PlaneTruth]

"Contrails trap heat in the atmosphere by reflecting infrared radiation emitted from the Earth's surface."

I believe just the opposite of a study commisioned after 9-11.
The minimal airtraffic immediately after 9-11 proved conclusively how contrails coallesce into high Cirrus. The beliefs expressed by the researchers was that while the clouds may trap some heat in, they also serve as an umbrella reflecting much IR radiation out.

More study required for sure.

PT

[Notso Fantastic]

<<Contrails could be eliminated if aircraft reduced their altitude from about 33,000 feet to between 24,000 feet and 31,000 feet...... if planes flew low enough to leave no contrails behind, their fuel consumption would increase by only four per cent>>

These people don't know what they are talking about. When climate scientists decide to look into areas not their expertise, then they come out with garbage like this. Had to fly back from MIA unexpectedly below 29,000' all the way instead of 33-39,000'. We used a darn sight more than 4% extra. To go even further down to 24,000'- we would not have made it- the differential would be large. Their figures are nonsense, so don't trust the rest of it! I shouldn't give it any further thought!

[Airbubba]

Here come the chemtrails folks and the "environmental activists"...

[Dr Dave]

I'm definitely not a Chemtrails person!

Anyway, the paper to which the New Scientist article refers is this one:

'Reducing the climate change impacts of aviation by restricting cruise altitudes'
Transportation Research Part D: Transport and Environment, Volume 7, Issue 6, November 2002, Pages 451-464
Victoria Williams, Robert B. Noland and Ralf Toumi

I have an electronic copy of the paper on my screen.

To clarify, the calculated increased fuel burns are the result of a complex simulation using a reorganized air traffic control mathematical simulator (RAMS) for Europe only (i.e. it may be weighted towards short haul flights and it also appears to allow for a reorganization of the air traffic management structure). They concede that their simulations produced variable outputs depending on the parameters, including a 7.2% increase under some circumstances. 3.9% is the weighted mean.

Note that the conclusions do not advocate that such a reorganisation of air traffic should be undertaken, just that the results are interesting:
'The results presented here indicate that a strategy to avoid the production of contrails by restricting cruise altitude could provide a net benefit to climate, despite the associated increase in CO2 emission. The analysis suggests that the implications for controller workload present the most likely operational obstacles to such a scheme and that reconfiguration of airspace would be required to mitigate the impacts.'


The study of the effects on surface temperature of Sept 11th is this one:
Nature Volume 418(6898) 8 August 2002 p 601
Climatology: Contrails reduce daily temperature range
Travis, David J.*; Carleton, Andrew M.†; Lauritsen, Ryan G.*

Again, I have a copy.

They conclude:
'Our findings indicate that the diurnal temperature range averaged across the United States was increased during the aircraft-grounding period, despite large variations in the amount of cloud associated with mobile weather systems (Fig. 2). We argue that the absence of contrails was responsible for the difference between a period of above-normal but unremarkable DTR and the anomalous conditions that were recorded.'

In other words, there was clear evidence that contrails affect short term surface temperatures. No conclusions were drawn about the impact on global warming, but it does not seem unreasonable to hypothesise that the contrails have some role to play, be it positive or negative in terms of anthropogenic heating.

With regard to the science, the Intergovernmental Panel on Climate Change (IPCC) studied the role of aviation in global warming in detail (and continue to do so). Their detailed report is here:

http://www.grida.no/climate/ipcc/aviation/index.htm

With regards to contrails they said in the summary (there is more detail in the report)
( http://www.grida.no/climate/ipcc/aviation/007.htm#spm45 ):

4.5. Contrails
In 1992, aircraft line-shaped contrails are estimated to cover about 0.1% of the Earth’s surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth’s surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 in the reference scenario (Fa1), at a rate which is faster than the rate of growth in aviation fuel consumption.

This faster growth in contrail cover is expected because air traffic will increase mainly in the upper troposphere where contrails form preferentially, and may also occur as a result of improvements in aircraft fuel efficiency...The radiative effect of contrails depends on their optical properties and global cover, both of which are uncertain. Contrails have been observed as line-shaped clouds by satellites over heavy air traffic areas and covered on average about 0.5% of the area over Central Europe in 1996 and 1997.

4.6. Cirrus Clouds
Extensive cirrus clouds have been observed to develop after the formation of persistent contrails. Increases in cirrus cloud cover (beyond those identified as line-shaped contrails) are found to be positively correlated with aircraft emissions in a limited number of studies. About 30% of the Earth is covered with cirrus cloud. On average an increase in cirrus cloud cover tends to warm the surface of the Earth. An estimate for aircraft-induced cirrus cover for the late 1990s ranges from 0 to 0.2% of the surface of the Earth. For the Fa1 scenario, this may possibly increase by a factor of 4 (0 to 0.8%) by 2050; however, the mechanisms associated with increases in cirrus cover are not well understood and need further investigation.


To say that these scientists do not know what they are talking about on the basis of third hand information would seem to be somewhat naive. Read their reports first-hand (all IPCC reports are available online for example), then make a decision.

This is a serious issue for aviation. The vast majority of climate scientists now accept that some anthropogenic global warming is occurring (IPCC involves about 1000 experts from universities, research centres, business and environmental associations, and other organizations in approximately 120 countries). As a result, the pressure to see reductions of change-causing processes is going to increase in the future. Aviation would be well-advised to act in a pre-emptive manner rather than have regulation imposed upon it. Burying our collective head in the sand is an unwise policy, whether you believe in the science or not.

Apologies for the long post

DrDave

[AhhhVC813]

This sort of nonsense is staggering in its naivety. It conveniently ignores the fact that any increase in fuel consumption, particularly on a long haul flight, may mean a reduction in payload to carry the extra fuel burnt. This payload would then have to be carried on another aircraft, burning yet more fuel and the domino effect would almost certainly mean a larger overall increase in CO2 emissions, surely outweighing any of the so called benefits from reflection of radiation by cirrus clouds.
Put any longhaul aircraft more than 4000 feet off its optimum altitude and the increase in burn is going to be closer to 10% than the 3.9% 'weighted mean'. Most 747s, 777s and 340s in ISA conditions are likely to be close to optimum cruise altitude at FL330 after a MTOW departure; they are also likely to get up to FL350 or metric equivalent within three hours of departure.
At lighter weights, on shorter (ex Europe to East Coast USA, Middle East, India, Pakistan etc.), they like to get to FLs above 370 straight away, therefore inflicting at least a 6000 foot deviation from the optimum.
Still, as we are in the U.K, according to experts, probably reaping the seeds of global warming, because we're actually having a summer, they must be right..................

[747FOCAL]

Just think of what lower and slower would do to ETOPs?? :{ No more polar routes.

Even if you design and build an aircraft that is optimum at the lower altitudes it will be a generation or two before you see any benefit as there will be so many aircraft already in use that are not optimum at that altitude.

:ok:

[Notso Fantastic]

Dr. Dave and Thread Bear (sounds like childrens show characters), they are quite simply using faulty data to produce the result they want! <<They concede that their simulations produced variable outputs depending on the parameters, including a 7.2% increase under some circumstances. 3.9% is the weighted mean.>> If you are going to limit jets to 24000' maximum when they are designed to go at 35,000'+ for efficiency (and the B777 higher still), then it is going to cost a darn sight more than 3.9% or 7.2%! Trouble is, these people look up in the sky and see those contrails and think what a shame they appear to be screwing up the ecology (that is until they want to go somewhere hot and sunny when it's OK for the world to make the sacrifice). So they grab hold of faulty data to prove what they want.
Watch my (virtual) lips- they are wrong. They are using faulty data. Therefore the world will be using up vastly greater resources and producing more pollution to get the job done if these idiots start getting people to believe them! Me- I don't care. If I am made to go below 24,000, suits me- I'll be getting less radiation, flying everywhere lower and vastly slower and not getting so out of breath. But you know it is just a left wing/chemtrailer/Greenpeace creep conspiracy, don't you?

[Thread Bear]

Thank you for sharing your opinions there Notso Fantastic. All kinds are welcome.

I posted this article to see the view of others on the matter. I am by no means a tree hugger or staunch greenie but I am INTERESTED.

Thanks Dr Dave for shedding more light on the topic, and the others that contributed.

T.B

[HectorusRex]

This discussion about greenhouse gases and global warming would appear to depend on faulty assumptions.

The basic source of heat on Earth is Solar radiation, and any upset of the Atmosphere and Stratosphere which results in an extended cloud cover will result in a reduction of Solar Radiation reaching Earth, and a consequent temperature REDUCTION, which is not what the Tree-huggers et al preach.
One only need study what happens in a desert with clear skies, where unimpeded solar radiation in daylight raises the temperatures to very high levels, whereas at night the reverse is true with the net outflow of long-wave radiation causing night time temperatures to plummet.

During World War II, Allied POW’s incarcerated in German POW Camps spent as much time as possible sun bathing to compensate for the reduced vitamin intake of the prison diets.
With the advent of the Allied daylight bombing offensive, huge flotillas of B-17 and B-24 aircraft of the USAAF caused massive contrails to form, and which rapidly spread to become a high overcast spreading from horizon to horizon.

The results were a marked drop in air temperature, and disgruntled prisoners, who missed out on sun bathing and were forced to don more clothing.
:confused:

[Dr Dave]

HectorusRex

I'm afraid your post is over-simplifying a very complex system.

The key to increased temperatures due to changes in atmospheric composition comes from the relative transparency of the atmosphere to various types of radiation.

The Earth receives energy from the sun in the form of shortwave radiation. It re-emits it in the form of long wave radiation. For constant temperature the amount coming in must equal the amount going out.

This is basically illustrated in the following diagram
(http://www.yale.edu/ceo/images/GuideFig1.gif):

http://www.yale.edu/ceo/images/GuideFig1.gif

A the top, the curve on the left is the spectrum for incoming radiation, the one on the right for outgoing.

At the bottom, the wavelengths of radiation absorped by different atmospheric gases are shown. So on the far left (short wavelength) is ozone, which absorbs high energy radiation, protecting the surface.

Note that H20 appears several times, as does CO2 etc. So changing the concentrations of these gases changes the amount of energy being absorped in different parts of the spectrum.

Overall effect is that changing atmospheric chemistry probably changes the balance between incoming and outgoing radiation, and thus changes global climate.

Unfortunately CO2 and water vapour are more effeicient at trapping long wave than short wave radiation, so increasing their concentration in the atmosphere will lead to more radiation being retained than is being emitted. The effect of this is increased temperature.

The smoking gun, to coin a phrase, is the Vostok ice core, from which it was possible to determine global temperature over the last 150,000 years and, by extracting gas bubbles, to measure the atmospheric chemistry.

The two curves are plotted here (sorry can't find a way to link this):

http://www.geocraft.com/WVFossils/temp_vs_CO2.html

Given the correlation between these curves can you really argue that levels of CO2 are not linked to temperature?

By the way this core was drilled and analysed by Russian scientists before the end of Communism. Notsofantastic, I bet you didn't realise your conspiracy was so far reaching? :D

DrDave (rather relishing being a children's show character!)

[Notso Fantastic]

Dr.....most interesting. But may I say a little simplistic? <<The Earth receives energy from the sun in the form of shortwave radiation. It re-emits it in the form of long wave radiation. For constant temperature the amount coming in must equal the amount going out.>>....this is quite ignoring the heat energy within the earth, and how much is leaking to the surface. We all know it's pretty hot down there. The thing is, the earth is not constant, Ice Ages come and go, everything cycles. As I see it, all the alleged pollution mankind produces is but a mere trifle compared to a resounding 'burp' from a damn good volcano- the sort of volcano Mamma used to make- a Mt. St. Helens or Pinatubo or Montserrat. If the world is global warming, it's doing it anyway- we really are not that influential. I'm told simultaneously I am causing global warming for which I will get zapped with a new Ice Age, and yes- I'll get stuffed when the Poles change around and then where will my compasses be? I hope I will be in Cyprus enjoying a bit of global warming for the next 50 years!
I have gone from being a member of Friends of the Earth and Greenpeace to totally regarding such organisations as 'political' and cynically against anything to do with 'progress'. We are not going to save the Earth by preventing a motorway being built- forcing people out of cars onto disgusting UK public transport will achieve nothing (they will pay whatever it takes to avoid such a fate). Concorde harms nothing.

[Dr Dave]

Notso fantastic

Again, you raise some interesting points.

Addressing your points in turn:

>This is quite ignoring the heat energy within the earth, and how
>much is leaking to the surface.

Fair point, but it is easy to show that the amount of energy transfered to the surface from geothermal heat is trivial in comparison with the amount of energy coming in from the sun. Proof of this can be seen on the Antarctic continent, which has ice frozen to the bedrock across most of the land surface. If geothermal heat was so significant it would melt the bed.

>We all know it's pretty hot down there. The thing is, the earth is
> not constant, Ice Ages come and go, everything cycles.

True, ice ages are controlled by the Milankovic Cycles, which are associated with changes in the orbital characteristics of the Earth. The next Ice Age will come, pretty much regardless of what humans do, though we may delay it a little. But these changes occur on 100,000 year cycles (the last glacial maximum was c. 20,000 years ago, the last interglacial c. 100,000 years ago). The change we are seeing occurs on a much shorter timescale, and is occurring MUCH faster than any other change we can find in the geological record, except the extinction events (which is a warning in itself).

> As I see it, all the alleged pollution mankind produces is but a
> mere trifle compared to a resounding 'burp' from a damn good
> volcano

Yes, volcanoes have a big influence. But their impacts are a short burp, followed by a long period without burps. What we are doing is releasing a constant stream.

Taking CO2 for example, annual anthropogenic emissions are thought to be more than 150x the annualised emissions from volcanic sources (Gerlach 1991 if you want to know the source of this)

Taking sulphur, volcanic and other natural sources = 25 Tg / year. Human sources = 79 Tg (i.e 3x as much) (source = Andres and Kasgnoc 1997)

We can show that a big volcanic eruption does change climate (no-one denies this). If we are putting so much more into the atmosphere, isn't it logical that this will affect climate too?

> I have gone from being a member of Friends of the Earth and
> Greenpeace to totally regarding such organisations as 'political'
> and cynically against anything to do with 'progress'.

I can't argue with that! Doesn't change the reality of the science though.

DrDave

[lizardlikeme]

Just to add to DrDave above,

The presence of CO2 (and many other "greenhouse" gases) in the atmosphere is natural - because of the presence of these gases (the physical properties of which DrDave described), the effective temperature of the earth is greater than it might otherwise be - hence life is sustained. The issue at stake within the climate change debate is increases in concentrations of these greenhouse gases above background levels. Consequently, especially with regard to the role of Milankovitch forcing on 100, 41 an 20kyr timescales, any climate change signal will be small, and nested within much greater variability through time.

Hence regarding 'circumstantial' evidence of climate change, then it is necessary to regard it with a degree of caution. For example, shrinking Alpine glaciers are often cited as evidence for climate change, but this ignores more immediate and identifiable explanations, such as adjustment of ice masses from little ice age maxima, or the role or regional variability of climate

[Notso Fantastic]

Who knows how much internal energy is released by volcanism? Although Antarctica may be frozen solid, I read they are just discovering massive thermal vents in the Indian Ocean. Anyone guess how much heat is released into the oceans to eventually find its way upwards? Add on surface volcanos and hotspots, and it will dwarf the energy we coax out of atoms and coal and gasoline.

We are facing numerous extinction possibilities:
Volcanos and Deccan Traps
Meteors
Diseases
English Cricket team
Maybe I'm getting cynical, but I just can't lie awake at night worrying about all those 500 year McDonalds containers, or the people using faulty scientific logic to just plain make life harder for the rest of us!
As a matter of interest, I am flying a 747 to JFK tonight. I shall ask our flight planners to produce a flight plan restricted to 24,000' to compare. Of course, not everyone would get 24,000'. Based on current experience, we would have loads of flights restricted to 18,000' or below (with the whole world crowding into 24,000')! Hopefully an answer Sunday.

[Danny]

"Maybe I'm getting cynical"Perish the though. Humph! :hmm:

Look forward to the answer, hopefully, on Sunday. :8

[Dr Dave]

Notsofantastic

Actually it is quite simple to measure the geothermal gradient and energy balance. For example there have been numerous deep boreholes drilled into the Earth's crust, both in the oceans and onland, and measurement of the geothermal gradient occurs routinely.

In addition, there has been very extensive measurement of ocean temperature such that the global ocean heat flux is now well constrained.

Finally, deep earth geophysics tells us how much radioactive material there is down there in the core, so it is quite easy to calculate how much heat is being released.

There are various other ways too - trust me, it's covered (I can send you scientific articles to this end if you wish)

All of this suggests that the amount of energy being released is trivial compared with the solar flux. Of course it is much greater than that being released by humans - but it is not our release of heat that is the problem - it is the release of gases that then cause trapping of energy. An analogy would be old fashioned airliners with manual controls - when you move the joystick it is not the energy input that you put into the system that actually turns the aircraft, it is the effects of that input in terms of deflecting the ailerons that turns the aircraft. Same with global warming - it is not our heat output (which is trivial) but the by-products - gases - that are causing change.

Yes, we do face numerous extinction possibilities (not sure what you mean by Deccan traps though - the Deccan Traps are a volcanic area of India that erupted 60-65 million years ago, now essentially inactive), but all are very low probability. Global warming is on a different probability level, although to say that it is likely to cause human extinction is really scare-mongering.

I still think you are missing the point of the article (see my original posting). The article considered European airspace over a small area - i.e. lot's of short trips at relatively low altitude. It did not consider transatlantic service, which would yield very different results. Of course if you compare a single long haul trip (i.e. your trip today) at high altitude you will get very different results. I will be very interested to see how different though?

Finally, I should reiterate that this was a scientific paper exploring possible scenarios. The authors did not advocate that airspace changes like this should be undertaken, just opened up the debate about possible measures that could be employed. Science advances through hypothesis setting and validating / rejection. That is rather different from stating that this is the measure that should be employed. I agree though that the New Scientist interpretation was unhelpful.

Notsofantastic - if you would be interested in exploring whether we could put together a scientifically-valid argument, perhaps using the sort of data to which you allude, against the contents of the paper then please contact me directly. I would be very happy to help you do this (research is my expertise).

DrDave

[ORAC]

I fear someone is being disingenuous,

The text of the original article did not state it was limiting itself to discussing short haul flights. On the contrary, it went out of it's way to say that, "But global air traffic is growing by around 3.5 per cent per year, and many of those extra flights are long-haul, high-altitude, contrail-forming journeys."

The figures are stated as being a simulation of that over the busiest part of Europe, taken together with the comment above, it is an obvious attempt to imply that it represents the future level of global long haul traffic.

I believe the point being made is valid. This was either badly written, with the comment about long haul traffic being an irrelevant aside, more probably it was introduced intentionally, even though unsupported by the data.

[Pax Vobiscum]

A very interesting thread. A couple of observations which I'd be grateful for Dr Dave (or anyone else) to comment upon:

(a) There is incontrovertible evidence that global CO2 levels have increased substantially over the last 150 years (and are continuing to increase, although the rate is slowing). The evidence that this change has resulted in global temperature increases over the same period is much thinner.

(b) Models of the earth's climate are still pretty crude. One of the biggest problems is lack of computing power which forces the use of very coarse grids (around 1km square) which can take no account of smaller-scale phenomena such as clouds. Another problem is our lack of understanding of how the climate actually works! Estimates of future global warming amount (IMHO) to little more than a best guess.

[bluskis]

Dr Dave's graphs, the linked ones that is, do indeed show a possible link between CO2/T in the fluctuations over 250,000 years.

However what is missing are graphs over the same period linking CO2/T/Airliners/human activity.

The graphs do not of course explain conclusively whether CO2 increases are caused by increased T, through the effect on lifeforms and the capacity of water to hold CO2, or whether the increase in CO2 from some source causes the increases in T.

As some have pointed out the sun's fluctuations, and our varying distance from the sun , are the prime source for climate change, and in its own small way this European summer, linking with a recent double top in solar activity, and the recent increase in the same in June/July tend to back up this proposition.

That said, contrails and aircraft high altitude emissions, which may not get recycled into the lower atmosphere, should be studied.

Afterall, human activity did cause London smog and cholera outbreaks. Not Linked though, except as human activity.

[Dr Dave]

ORAC

No, I don't think I was being disingenuous.

The article quite explicitly states that the results are valid only for this area, and would differ if a larger area were considered.

I quote directly from the original text (my parenthesis):
'The results of this case study predict an annual fuel burn change only for the traffic mix and atmospheric conditions of the five states region in Europe. Other regions would be expected to
have a different seasonal cycle of maximum permitted cruise altitudes dependent on the local atmospheric conditions. The fraction of flights affected by those altitude restrictions would be
dependent on the nature of the traffic mix.'

This is explicitly saying that the results reported here are not applicable more widely.

They do also explictly discuss the problem of long haul aircraft, but note that because this was a Europe based study it is not considered in the article:

'Some long distance flights may also be unfeasible with current aircraft as less efficient operation at lower altitude may reduce their range. These issues are not relevant to this analysis of European airspace, but would be for a global study.'

Pax Vobiscum

Commenting on your two points:

(a) There is incontrovertible evidence that global CO2 levels have increased substantially over the last 150 years (and are continuing to increase, although the rate is slowing). The evidence that this change has resulted in global temperature increases over the same period is much thinner.

I'm afraid that your assertion that the increase in levels of CO2 is reducing is not true as far as I know. This graph is an illustration of global CO2 levels. The acceleration is evident:

http://www.cru.uea.ac.uk/tiempo/floor0/briefing/vietnam/co2conc.gif

Yes, the absolute prrof is still lacking, but the evidence is definitely strengthening all the time. More importantly, many of the problems with the anthropogenic greenhouse effect are now being dealt with. Most (but not all) climate scientists are now pretty convinced.


(b) Models of the earth's climate are still pretty crude. One of the biggest problems is lack of computing power which forces the use of very coarse grids (around 1km square) which can take no account of smaller-scale phenomena such as clouds. Another problem is our lack of understanding of how the climate actually works! Estimates of future global warming amount (IMHO) to little more than a best guess.

If anything, you are being too generous to the modellers! Last I heard (18 months or so ago) the Hadley Centre (UK Met Office) regional simulation worked on grid squares of 50 x 50 km. As far as I know, large scale simulations are not being undertaken on a scale of 1 x 1 km.

However, just with weather forecasting, that level of resolution is not really needed. Climate models have a long way to go, but are definitely getting better, and actually appear to be getting quite good now.

DrDave

[lizardlikeme]

Regarding Pax and Dr Dave above,

The resolution of the Hadley Centre Regional Models is 0.44*0.44 lat lon. These models are currently available for a European window, and I think over the Indian Subcontinent as well. The resolution of the global scale models is 3.75*2.75 lat lon, which gives effectively ~7000 grid cells, of which there are around 19 atmospheric levels, and 20 oceanic levels. To give some idea of how this translates into reality, the UK is taken care of by only 6 grid boxes.

All is not lost though for regional climate scenarios - there are a number of downscaling techniques which are available and effective (some of which I have used in research) to resolve the scale mismatch between the output of global climate models, and the needs of the climate change impacts community

[HectorusRex]

My initial reply may well have been over simplified, but that does not necessarily signify inaccuracy, Dr Dave.

You have very eruditely produced data and facts to back your stance, and I note your belief in the increase in CO2 levels.

Basic photosynthesis, as you will know, is the process that converts energy in sunlight to chemical forms of energy that can be used by biological systems. Photosynthesis is carried out by many different organisms, ranging from plants to bacteria. All these organisms convert CO2 (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions.
All the food we eat and all the fossil fuel we use is a product of photosynthesis, and with a rapidly burgeoning world population, even more of the building blocks of photosynthesis become essential to provide the food and fuel supplies necessary to support this population growth.

Does the increase in CO2 levels not signify that we now see an increased food supply for these plants and organisms, and also that this supply is where it can be used, namely where these biological systems exist?

Weather, and the study of it has been long and involved, but most have agreed that apart from any other factors, weather patterns have always been chaotic, and temperature fluctuations have existed since long before mankind exerted any influences on the atmosphere.

[Dr Dave]

Herctorus Rex

Not sure where I implied that your facts were inaccurate? If I did, my apologies. Not my intention.

With regard to biological productivity - yes, it is a little reported by-product of CO2 elevations that biological productivity increases - off the top of my head it has been estimated that increased CO2 has been responsible for a 4% increase in crop yields in temperate areas?

However, it is undeniable that increased productivity is not compensating adequately for increased CO2 production - otherwise levels wouldn't be rising. The fact is that this increase is tiny compared with the growth in world population, and certainly is not the answer to those problems. Add to that the poitential loss of productivity to aridity if, as predicted, climate zones move.

Some calculations have been done of the amount of increased tree planting that would be needed to compensate for the emissions from humans. Generally, the figures come out as follows (from Goreau 1992):

'A major part of global warming could be averted if the addition of CO2 to the atmosphere were accompanied by equal removal. Emitters could pay for planting, growing, and sustaining enough biomass and storage to remove excess carbon permanently. It would require trees that consume 10 tonnes of carbon per ha per year on 4 million km2 of land, to ensure removal of the current carbon increase. The area could be as low as 2 million km2 in the humid tropics, if reforestation stopped, or as high as 8 million km2 if areas with long dry seasons or colder temperatures were planted.'

(I haven't checked these numbers though).

Weather is a chaotic system, but as with many non-linear systems order emerges (that is climate). We are getting better and better at modelling this ordered behaviour from the non-linearity. Of course temperature fluctuations have occurred previously (and my very first post in this thread demonstrated that explicitly). The fact remains that, except during extinction events, the rapid changes in global temperature that we are currently measuring do not appear to occur in the geological record, and that our observations of increased atmospheric temperature are consistent with the results from Global Climate Models when increased CO2 levels are input. Add to that the clear linkage between palaeo levels of atmospheric CO2 and temperature (with the rider that cause and effect are hard to interpret as per bluskis post), and the argument becomes reasonably strong.

DrDave

[ORAC]

Dr Dave,

We seem to be at cross purposes.

The text you quote is not in the article posted at the beginning of this thread by Thread Bear. It may well be in the paper which you then posted. In which case I reiterate my point, someone (albeit perhaps the NS journalist) omitted the caveats and phrased the article to imply that long-haul flights are/were responsible.

[Thread Bear]

Okay, at the end of every good study there must be some conclusions drawn and I have spent so much time reading about this subject over the last few days I am braindead.

Probably the best I can come up with thus far is that this subject is far more extensive than can be discussed in a 1000 word article in a magazine, accompanied by this picture that initially caught my attention.

http://www.newscientist.com/ns_images/9999/99992926F1.JPG

One ounce of information has led me onto another and another and so on... it is literally neverending. The technical/scientific assessment and results of which must have inspired this article were derived from the studies of the IPCC.

This is by no means a simplified answer or conclusion to this thread...

http://www.grida.no/climate/ipcc/aviation/index.htm - Chapter 2.4 does offer "Conclusions and Overall Assessment of Present Aviation Impacts on Ozone".

Bottom line of what it says (or the top line actually!) is
Currently, there is no experimental evidence for a large geographical effect of aircraft emissions on ozone anywhere in the troposphere.

It is a snippet from a LOT of information.

[Dr Dave]

Thread Bear

Good diagram. It is very scary when you start to dig to find just how much research is going into this field. Last weeks INQUA conference, looking just at climate change during the period 2.5 million - 11,000 years ago had over 1,100 scientists attend to present their research. This is only a small proportion (probably <10%) of the total number of climate and atmospheric scientists working on cliate change. Wading through the scientific output is a major challenge!

Unfortunately, the ozone conclusion that you highlight, although highly relevant, is not a conclusion about overall heating as ozone is just one of a range of greenhouse gases.

My feeling is that the key conclusion of the IPCC report in relation to aviation is this one:
http://www.grida.no/climate/ipcc/aviation/008.htm

The climate impacts of different anthropogenic emissions can be compared using the concept of radiative forcing. The best estimate of the radiative forcing in 1992 by aircraft is 0.05 Wm-2 or about 3.5% of the total radiative forcing by all anthropogenic activities. For the reference scenario (Fa1), the radiative forcing by aircraft in 2050 is 0.19 Wm-2 or 5% of the radiative forcing in the mid-range IS92a scenario (3.8 times the value in 1992)

In other words, the best estimate is that aircraft are responsible for 3.5% of the anthropognic greenhouse effect, rising to about 5% over the next 50 years or so.

ORAC - fair enough. In my view the ways in which journalists 'misinterpret' fact is scandalous.

DrDave

[Thread Bear]

Yes, you are right.

Are you sure you're not an IPCC Professor incognito, Dr Dave?

Thanks for your insight.

T.B :ok:

[Pax Vobiscum]

Comment from Philip Stott (retired prof of biogeography) in today's Times:

Claims about global warming are worse than hot air, they poison the atmosphere (http://www.timesonline.co.uk/article/0,,482-770693,00.html)

[Notso Fantastic]

DR. Dr!, as promised, having had an amenable Flight Planner for our flight on Thursday, he kindly ran through the Big Airways flight planning computer comparison figures for a New York flight limited to 24,000' as compared to the standard altitude requirement. This was for a B747-400 on 07 Aug 2003. The common figures are:
Zero Fuel Weight 220,000 kgs
Payload 31,700 kgs
Planned Fuel remaining at Destination 10,700 kgs

Standard
Step climbs at approximatel quarter points 34,000', 36,000' and 38,000'
Fuel required to destination 62,739 kgs and time 06.48

Altitude Restricted
Limited to 24,000'
Fuel required to destination 72,616(*) and time 06.44

(*) Note. The flight planner was unable to prevent the computer desperately wanting to climb once the Oceanic leg was completed. At 1.45 hrs from New York, the computer assumed a climb in the remaining time to 40,000' to try and save a bit of fuel, so the actual 'all the way figure at 24,000' would have been several hundred kgs higher.

Thus limiting cruise to 24,000' all the way would have consumed more than 10,000kgs extra fuel on top of the 62,739 actually used through a high level cruise. What surprised me was the time factor- actually slightly quicker at 24,000'. The burning question of the day, therefore, is:
"Is it better to reduce contrail pollution by burning an extra 16% (approx) fuel and producing that much extra exhaust pollution?"

Another relevant point- high altitude air is not floating around up there forever- like on surface meteorological charts, it moves horizontally. Over surface high pressure areas, the air subsides from high altitude (thus creating poor visibility hazy conditions that doesn't clear easily as particles are not removed from near the surface), over low pressure areas, air rises, clearing the atmosphere but producing cooling condensation into cloud. Therefore the minute amount of water injected into the atmosphere will eventually find its way back into the water cycle. I'm afraid this research team have been bending facts to make it fit their hypothesis!

Now Dr., about me back.............

[PaperTiger]

Between 24000ft and 31000ft contrails do not formBzzzt ! Wrong. I judge the rest of this science based on that peculiar statement.

[Dr Dave]

PaperTiger

I am sorry, but you, like many others, are drawing incorrect conclusions about this research because you have not read the actual source.

The authors of the paper (i.e. the scientists) DO NOT say that contrails do not form between 24,000 and 31,000 ft. Indeed, they say explicitly that they do. What they say is that the height of widescale contrail production varies hugely (and provide a mathematical function to describe this). As a result they are investigating the effects that would occur if cruising altitude were restricted when contrails can be formed at these altitudes.

In their calculations, the suggest the following:
June - September: altitudes up to 31,000 ft would be allowed, as contrail production at lower levels is limited (NOT zero though)
Nov-Jan: altitudes would be limited to 24,000 (or thereabout) as contrail production at higher levels is quite high
Other months: altitude varies between 24,000 and 31,000 ft

There is a graph in the paper to decsribe this

The 3.9% increase in CO2 production as a result of these altitude limitations seems to be quite in keeping with the very interesting figures provided by Notso Fantastic, given that this paper considers predominantly short-haul flights. Again I remind you that the authors explictly recognised that when long-haul flights were considered the figures would change:

'The results of this case study predict an annual fuel burn change only for the traffic mix and atmospheric conditions of the five states region in Europe. Other regions would be expected to
have a different seasonal cycle of maximum permitted cruise altitudes dependent on the local atmospheric conditions. The fraction of flights affected by those altitude restrictions would be
dependent on the nature of the traffic mix.'

Notso Fantastic, I can't work out what your comments about the hydrological cycle are meant to show. No-one is suggesting that once injected at high altitude the water stays there. Of course it is redistributed and rejoins the hydrological cycle. However, under current conditions the water is replaced by further air traffic, meaning that there is a nett long term impact.

This point was beautifully illustrated by the other research that we have been discussing, in which N. America became essentially contrail free during the short period of the Set 11th shutdown.

Oh, and by the way, I'm not that sort of Dr...but my wife is a physio if you need help for your back. :D

DrDave

[HectorusRex]

A very recent letter on Climatology and disagreement with the Kyoto Protocol was sent to the Candadian House of Commons.
The link is Here (http://www.sepp.org/NewSEPP/LttrtoPaulMartin.html)

It provides a contray opinion to Dr Dave.

It merely serves to demonstrate that there is no absolute certainty in this topic, just as weather forecasting is sometimes described as:"Weather forecasts are horoscopes with numbers":ok:

[Dan Winterland]

There seems to be a lot of 'interpreted statisitics' with reference to global warming. Scientists who seem to be frequently pushing their theory for career furtherment and fame, pick and chose the stats they need to prove or disprove. In the 1970s, some scientists were claiming to have proved with the data they had that there was incontavertable evidence that we were heading for another ice age. I wonder where they are now?

One statistic which we don't hear much about is that volcanic activity pushes out more CO2 into the atmosphere than all the man made activities put together. The fact that volcanic activity has been markedly on the rise since 1980 may have something to do with temp rises.

"Lies, damn lies and statistics". (Disreli).

[Dr Dave]

Dan Winterland

Lies, Damn Lies and Statistics indeed.

Data from Middleton (1998), amounts in millions of tonnes of carbon per annum

Combustion of fossil fuel: 6000
Land use change (deforestation and biomass burning): 1600

Metamorphism and volcanism 120
Weathering: 220

Probably serves to show how much misinformation there is out there.

DrDave

[steamchicken]

I suspect a lot of people who describe themselves as so-called "contrarians" on this issue are influenced by the fact that all their arguments tend towards not having to do or spend anything themselves. It's generally a sign of bad thinking when - completely by coincidence, obviously - all your arguments favour your own interests!

PS, Dr. Dave - interesting stuff...

[Notso Fantastic]

It's nothing to do with ones own interests, it's to do with believing insufficient or faulty research. Back in the 70s, we were continually being told that the next Ice Age was just around the corner. Now it seems to have disappeared into 'Global Warming' will get us all. Periodically we get things like coffee consumed with bacon creates carcinogens, next coffee is actually good for you. Salt is currently out of favour- what's the betting within a few years salt will be regarded as good again? But when you are presented with scientific 'facts' that present a case, and you see that there are errors in assumptions leading up to those conclusions, then there is a good case to disregard faulty and insufficient research. When Biogenetic companies fund 'independent' research that proves that biogenetic products are harmless, should we necessarily believe them? Without knowing exactly where this theory about contrails comes from, and who funded it, or is it a personal opinion coming from a rabid 'green', then the results are to be treated with great suspicion, especially as this one seems to have made some broad assumptions that are erroneous. It was mentioned back at the beginning it was an old news item?

[Dr Dave]

Notso Fantastic

Fair comments, but surely part of the problem is that people are willing to pass comment based on inaccurate information (look through the thread for a number of examples). This muddies the water to a very high degree. At the end of the day, as a research scientist myself, I continually come back to the feeling that good science is undone by poor (often very poor) reporting by journalists. This seems to be a problem we share with the aviation community.

For information, the original paper openly details the source of the funding:

'This work was supported by the Engineering and Physical Sciences Research Council as part of a feasibility study in the Future Integrated Transport Programme.'

EPSRC is the UK government research funding body for engineering: www.epsrc.ac.uk

DrDave

[tocamak]

But is it not really all that relevant as we are going to run out of oil within the next forty years or so, well according to New Scientist (2nd August) Energy special report.

[Notso Fantastic]

And now they've just found a new oil field near Winchester. They really are finding the stuff as rapidly as it is being used. If ever it starts running short, we haven't even scratched the surface of biological fuels yet.........

[Pub User]

Several of the posts above have mentioned this water that is "injected" into the atmosphere by jet engines. Unless my jet-engine theory knowledge is seriously flawed, there is no water "injected" by the engine into the atmosphere (except for a few seconds during the Harrier's hovering antics). The water vapour/ice crystals are simply gathered by the hungry engine and pushed out in such a concentration that they are visible.

Additionally, the fundamental argument that cloud cover produces a warmer Earth is utter rubbish. Last Friday it was 32deg C in my garden, but on Saturday we had cloud cover and it only reached 26. Or is it just Cirrus that warms the Earth, and all other clouds keep the heat out?

[Ignition Override]

If there is some pollution, then that is simply too bad. But our industry should be left alone-it is having a difficult enough time recovering (at least in the US) from TOO MUCH GOVERNMENT, i.e. those huge security taxes, which are not paid by the passengers. We have many thousands of airline people laid off, and this only includes the US. Yes, the US government recently paid the airlines back, at least for part of this, but just wait-our GOP is quickly closing the gap to become so over-regulated that it already appears to operate like the many heavy-handed foreign govts out there, which seem to believe that a gigantic bureaucracy with rigid regulations for everything, is more efficient than anything else.

Ozone or pollution-that's just tough. This issue should go to the very bottom of the problem priority list-whether the Green Party (i.e. German Foreign Minister Joschke Fischer) likes it or not. Many of them would rather live in the Iron Age in a village and/or in total anarchy. Maybe that is why so many anarchists/Communists are attracted to this party....("brilliant deduction, Einstein")....:yuk:

[bluskis]

Pub User

Fuel contains carbon and hydrogen amongst other elements.
Air contains nitrogen and oxygen amongst other things.

Reacting fuel and air in your jet engine results in the oxygen in the air combining with the carbon and the hydrogen in the fuel , forming carbon dioxide and water, again amongst other things.

[bookworm]

I didn't see any links to the papers in the preceding thread, so for those interested in reading the original research rather than dismissing it on the basis of an article written about it:

Reducing the climate change impacts of aviation by restricting cruise altitudes (http://www.cts.cv.ic.ac.uk/html/ResearchActivities/publicationDetails.asp?PublicationID=186)

and the more recent paper by the same authors with a more detailed analysis of the fuel burn consequences

Air Transport Cruise Altitude Restrictions to Minimize Contrail Formation (http://www.cts.cv.imperial.ac.uk/html/ResearchActivities/publicationDetails.asp?PublicationID=250)

[Pub User]

bluskis

You're right! I knew I should have concentrated harder in those Organic Chemistry lessons in sixth-form, but the girl opposite had such lovely legs ...........

I'll take the hit on that one, but while we're into chemical equations, what about the other one (cloudy day = warmer weather). I know about the change in diurnal variation with cloud cover, but the simple fact is that a cloudy day is a cold(er) one.

[bookworm]

The IPCC report (http://www.grida.no/climate/ipcc/aviation/040.htm) goes into some detail on the effect of cirrus cloud and contrail on warming. The key is that on average they keep more heat in than they keep out.

[Pub User]

A fascinating article, if a little unwieldy in its prose. However, it uses the word "may" no less than 24 times to present its case. This is hardly likely to convince any audience, particularly one consisting of professional pilots, who are used to dealing with practicalities any certainties.

NotsoFantastic tell us, above, that his 747 WILL use (approx) 16% more fuel if he flies at the levels recommended by the scientists. His company is not going to even think of allowing such measures without strong and persuasive facts.

Piloting is one of the few occupations in which one is required to take true responsibility, or put your money (life) where your mouth is. If scientists want to convince these people, they will have to have significantly more conviction than the author of the article has demonstrated.

[bluskis]

A little weighty in its prose is being polite.

Congratulations Bookworm for having the patience to read through it and precis it so concisely.

I can just picture the multilingual committee negotiating and voting on each and every paragraph in committee English, and squeezing their mates into the footnotes.

Still, as somebody remarked earlier, global warming has become an industry.

[Pub User]

Perhaps the precis was a little too concise.

Surely what Bookworm meant was: ".........they may keep more heat in than they keep out."

[TyroPicard]

Pub User

But cloudy nights are warmer than clear nights.

TP

[used2flyboeing]

This is a hugh issue - to add with the other two hugh issues ( 1) noise 2) emissions ) facing new aircraft designs - particularly HIGH ALTITUDE aircrafts, MULTI-ENGINE aircrafts - and MOST IMPORTANTLY - HYDROGEN POWERED AIRCRAFTS. ..I think Boeing has done a study on this - the problem with HYDROGEN & LOTS of HIGH ALTITUDE AIRCRAFTS is that the former GENERATES WATER VAPOR the persists at altitude for a very long time - now, if you load up the skys with these things - they could effectively start to impact the solar radiation comming through .. Now, if you are business paranoid Boeing - this is something else to mitigate a 10-30 billion new airplane strategy - There is still cold war nuclear bomb fallout persisting at very high SR71 altitudes - so everything that goes up - takes awhile to come down.. I knew a British air force engine mechanic who had significantly gotten exposed to distilled radiation - due to cleaning engine exhaust nozzles on high altitude British bombers or reconnassiance aircrafts during the 70s80s. Another big risk factor for the A380 is noise - risky to but 4 very large engines on an airplane in view of future unknown noise & emissions standards..