Paul Beckwith (climate scientist) on chemtrails

skephu

Senior Member.
Climate scientist Paul Beckwith has posted a Youtube video where he debunks chemtrails by proposing that cleaner jet fuel and the physical and chemical changes in the atmosphere due to global warming make persistent contrails last longer because they consist of much smaller water droplets / ice particles than before.



Basically he proposes that contrails behave very-very differently because of these atmospheric changes than they used to, and this is what leads to the large number of long-lasting trails.
 
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That may be true, but it plays right into the hands of chemtrailers. By "admitting" the skies have changed and that contrails don't behave like they used to, it's easy for chemtrailers to leap to "coverup".
 
I'm not really sure though whether he is completely right. I can accept his argument about a colder stratosphere and the increase in stratospheric water vapor. But he also says that because jet fuel is cleaner, the particles that serve as condensation nuclei in the exhaust are smaller, and therefore the contrail will be much more reflective and will last longer. But recent contrail research seems to suggest the contrary. For example:

Kärcher, B. "The importance of contrail ice formation for mitigating the climate impact of aviation." Journal of Geophysical Research: Atmospheres (2016).
External Quote:
The mitigation potential of altering the contrail formation stage is explored using a microphysical model to show how reductions in soot particle number emissions from jet engines, reductions in mean soot particle size, and a decrease in the supersaturation of aircraft exhaust plumes substantially lowers the optical depth of young contrails thereby decreasing the occurrence, lifetime, and radiative impact of contrail cirrus.
 
People have suggested climate change causing more contrails before, but I've never seen any evidence to back it up. For one thing the change in temperature is very small, but seasonal, diurnal, and weather related changes are huge. So it seems highly unlikely it would do anything more than very small average changes.

I'm rather skeptical of his claims in general.
 
I would like to see more numbers. A coherent set of data about the amount of (persistent) contrail coverage, increase in number of flights, atmospheric circumstances, possible feedbacks. And a scientific article about all that; not just a video.
 
I listened to the video and made some notes:

Firstly, I disagree that there are many contrails (certainly not persistent contrails) in the stratosphere, because the stratosphere is above the common vertical range of jet transport cruise altitude, and there is insufficient moisture for the air to be ice saturated.
So changes in the stratosphere, even lower stratosphere are not going to affect persistent contrails.
The increase in water vapor in the lower stratosphere seems very small.

It is unclear how "cleaner fuel" can "change the chemistry of the atmosphere".

Sulfur and soot are freezing nuclei, not cloud condensation nuclei (CCN).

There are plenty of natural CCN in the atmosphere that any increase provided by combustion products are not going to make any difference.

It is unclear how cleaner fuel (less sulfur) produces more and smaller contrail particles. I agree that more and smaller particles (if that were true) would make trails brighter.

It is unclear how smaller contrail particles make the contrails more persistent. I agree that if in fact they were brighter they may remain visibly detectable longer and appear to persist longer, but not to the extent of the chemtrail believers general claim (that contrails that used to dissipate now persist for hours).

I don't think climate scientist Paul Beckwith actually fully understands contrail formation and persistence.
 
Sulfur and soot are freezing nuclei, not cloud condensation nuclei (CCN).

There are plenty of natural CCN in the atmosphere that any increase provided by combustion products are not going to make any difference.
You sure about that?
External Quote:
For droplet formation by water condensation, cloud condensation nuclei (CCN) must be available. Ambient aerosol contains too few CCNs to explain the large number of ice particles (10[sup]4[/sup]—10[sup]5[/sup]/cm) required for the early visibility of contrails 10—30m behind engine exit (Kärcher 1996). In addition to entrained ambient aerosol, the CCN sources include soot particles and freshly nucleated sulfuric acid/water droplets (Kärcher et al. 1996), parts of which form on chemi—ions emitted by the engines (Yu and Theo 1998b).
From:
Schumann, U. (2002). Contrail cirrus (pp. 231-255). Oxford Univ. Press, Oxford, UK.
http://elib.dlr.de/9493/1/cntrcrr.pdf
 
I would like to see more numbers. A coherent set of data about the amount of (persistent) contrail coverage, increase in number of flights, atmospheric circumstances, possible feedbacks. And a scientific article about all that; not just a video.
Indeed. It's a hypothesis at best. But Beckwith presents it as established fact. He also seems to exaggerate the effect ("contrails behave very-very differently", etc.).
I have checked his publications and he has not published anything about contrails.
He should consult some of the actual contrail experts such as Schumann, Kärcher, Minnis, etc.
 
You sure about that?
External Quote:
For droplet formation by water condensation, cloud condensation nuclei (CCN) must be available. Ambient aerosol contains too few CCNs to explain the large number of ice particles (10[sup]4[/sup]—10[sup]5[/sup]/cm) required for the early visibility of contrails 10—30m behind engine exit (Kärcher 1996). In addition to entrained ambient aerosol, the CCN sources include soot particles and freshly nucleated sulfuric acid/water droplets (Kärcher et al. 1996), parts of which form on chemi—ions emitted by the engines (Yu and Theo 1998b).
From:
Schumann, U. (2002). Contrail cirrus (pp. 231-255). Oxford Univ. Press, Oxford, UK.
http://elib.dlr.de/9493/1/cntrcrr.pdf

CCN in the exhaust change the nature of the contrail, but even a hydrogen fueled plane leaves contrails.

http://history.nasa.gov/SP-4404/ch6-4.htm
External Quote:
On 13 February 1957, the first of three successful flights was made and the fuel system worked well.27 The transition to hydrogen was made in two steps. The hydrogen lines were first purged, then the engine was operated on JP-4 and gaseous hydrogen simultaneously. After two minutes of operations on the mixture, Algranti switched to hydrogen alone. The transition was relatively smooth and there was no appreciable [107] change in engine speed or tailpipe temperature. The engine ran for about 20 minutes on hydrogen. The pilots found that the engine responded well to throttle changes when using hydrogen. When the supply was almost exhausted, the speed began to drop. As this became apparent, Algranti switched back to JP-4 and the engine accelerated smoothly to its operating speed. The engine burning hydrogen had produced a dense and persistent condensation trail, while the other engine operating on JP-4 left no trail.
 
The engine burning hydrogen had produced a dense and persistent condensation trail, while the other engine operating on JP-4 left no trail.
This is not a good argument at all.
From Schumann U. On conditions for contrail formation from aircraft exhausts. Inst. für Physik der Atmosphäre; 1995.:

External Quote:
Engines burning liquid
hydrogen emit 2.6 times more water vapour than kerosene
for the same amount of combustion heat. Hence, contrails
form behind liquid hydrogen-propelled aircraft at typically
10 K higher temperatures
, i..e at lower tropospheric and
higher stratospheric alltitudes and may grow to larger
diameter before evaporating.

...

It should be noted that engines burning liquid hydrogen
will be essentially free of soot and sulphur emissions
(except
from burning air with sulphur containing molecules). It can
be expected that such engines emit far less particles than
engines burning kerosene. It appears likely that a smaller
number of particles emitted will lead to larger droplets and
ice particles. Such a contrail would exhibit a smaller optical
thickness in spite of the larger water content
, see Appendix
3. Moreover, the particles would sediment earlier than for a
larger initial particle density. This suggests that aircraft
burning liquid hydrogen will cause persistent contrails
which are of shorter life—time
, and possibly less climate
impact than aircraft burning kerosene.
 
Again from Schumann, U. (2002). Contrail cirrus (pp. 231-255). Oxford Univ. Press, Oxford, UK.:
External Quote:
Models suggest that con—
trails would also form without soot and sulfur emissions by activation from freez-
ing of background particles (Jensen et al. 1998c; Karcher et al. 1998a). However,
the resulting contrails would have fewer and larger particles and hence less direct
radiative impact.
This contradicts Paul Beckwith's suggestion that the ice particles in contrails are smaller due to the cleaner fuel.
 
Firstly, I disagree that there are many contrails (certainly not persistent contrails) in the stratosphere, because the stratosphere is above the common vertical range of jet transport cruise altitude, and there is insufficient moisture for the air to be ice saturated.
Correct for the second reason, but not for the first (IMHO). Plenty of passenger jets fly in the stratosphere. This week I have been looking at the soundings and the tropopause has been comfortably below 30,000 feet over the UK.

For instance see this one from Camborne a couple of days ago. The tropopause is at about 320mb, or just under 28,000ft!

image.gif


The result has been that the only persistent contrails I have seen have been unusually low, around 25-28,000ft, while higher jets have often not been leaving any trails at all, even short ones.
 
Just a note to any interested lurkers or chemtrail advocates reading this.....:rolleyes:
.....We will also argue against ideas "that may be in favor of contrails", if they don't hold up to scientific scrutiny.
 
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How do you get a graph like this?

This was from the University of Wyoming weather sounding page: http://weather.uwyo.edu/upperair/sounding.html

Choose "GIF: Skew-T" under "Type of plot".

The tropopause is marked by the point at which the temperature line (right-hand thick line) starts heading back to the right. The example I posted was very sharply defined; sometimes it is more of a gradual curve so harder to pinpoint.
 
You sure about that?
External Quote:
For droplet formation by water condensation, cloud condensation nuclei (CCN) must be available. Ambient aerosol contains too few CCNs to explain the large number of ice particles (10[sup]4[/sup]—10[sup]5[/sup]/cm) required for the early visibility of contrails 10—30m behind engine exit (Kärcher 1996). In addition to entrained ambient aerosol, the CCN sources include soot particles and freshly nucleated sulfuric acid/water droplets (Kärcher et al. 1996), parts of which form on chemi—ions emitted by the engines (Yu and Theo 1998b).
From:
Schumann, U. (2002). Contrail cirrus (pp. 231-255). Oxford Univ. Press, Oxford, UK.
http://elib.dlr.de/9493/1/cntrcrr.pdf

Hmm. Yes, I have seen this before. The assumption here is that there is a 1 to 1 relationship between an initial condensation particle and an eventual ice particle. I not entirely sure that is a safe assumption. There may be a process (and I have read it somewhere) in the freezing of a droplet that produces a large number of small ice particles. I know, citation needed, and I hope I can find it.
 
Correct for the second reason, but not for the first (IMHO). Plenty of passenger jets fly in the stratosphere. This week I have been looking at the soundings and the tropopause has been comfortably below 30,000 feet over the UK.

For instance see this one from Camborne a couple of days ago. The tropopause is at about 320mb, or just under 28,000ft!

View attachment 18679

The result has been that the only persistent contrails I have seen have been unusually low, around 25-28,000ft, while higher jets have often not been leaving any trails at all, even short ones.

SIGWX charts such as this one https://www.aviationweather.gov/products/swh/ show the height of the tropopause (boundary between troposphere and stratosphere) as Flight Level (in 100s of feet). They are the 3-digit numbers in the boxes. The one near Florida means FL450. The trope will be quite low pole-ward of the Polar Jet.
 
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