Friday, May 25, 2007

Clouds In Chambers

a cloud chamber in action

What do you do when you want to study clouds and all you have is balloons because airplanes are not very reliable and they are expensive? Like any good scientist you try to make clouds in your lab. Which is exactly what C. T. R. Wilson did in 1912.
The study of high energy particles was greatly aided in 1912 when C. T. R. Wilson, a Scottish physicist, devised the cloud chamber. The general procedure was to allow water to evaporate in an enclosed container to the point of saturation and then lower the pressure, producing a super-saturated volume of air. Then the passage of a charged particle would condense the vapor into tiny droplets, producing a visible trail marking the particle's path.

The device came to be called the Wilson cloud chamber and was used widely in the study of radioactivity. An alpha particle left a broad, straight path of definite length while an electron produced a light path with bends due to collisions. Gamma rays did not produce a visible track since they produce very few ions in air. The Wilson cloud chamber led to the discovery of recoil electrons from x-ray and gamma ray collisions, the Compton-scattered electrons, and was used to discover the first intermediate mass particle, the muon. Wilson was awarded the Nobel Prize in physics in 1927 for the development of the cloud chamber.
Why did Wilson invent the cloud chamber? It certainly wasn't to study nuclear physics which was in its infancy at the time. It really was the case that he wanted to study clouds.
Inspired by sightings of the Brocken spectre while working on the summit of Ben Nevis in 1894, he began to develop expansion chambers for studying cloud formation and optical phenomena in moist air.
So how did all this interest by people studying nuclear physics come about?
Very rapidly he discovered that ions could act as centres for water droplet formation in such chambers. He pursued the application of this discovery and perfected the first cloud chamber in 1911. In Wilson's original chamber the air inside the sealed device was saturated with water vapor, then a diaphragm is used to expand the air inside the chamber (adiabatic expansion). This cools the air and water vapor starts to condense. When an ionizing particle passes through the chamber, water vapor condenses on the resulting ions and the trail of the particle is visible in the vapor cloud.
Fun stuff. In fact it is so much fun that improved chambers have been developed that can make the required clouds continuously so that you do not have to keep re-pumping the chamber to get the required conditions for cloud formation. Mad Physics has a nice diagram of Wilson's original design and instructions on how to build a more modern version using methanol (wood alcohol), pure ethanol (the drinking kind), or pure isopropyl alcohol (used in diluted form in rubbing alcohol)and dry ice. Cornell University also has similar instructions along with a trouble shooting guide.

OK, so men have been making clouds in chambers since 1912. Since not long after that time we have understood that high energy nuclear particles can help clouds to form.

Which leads us to the question of climate and how our sun's magnetic field can affect climate. I wrote some about that in Clouds and More Clouds. As usual with any "new" science there are sceptics and deniers (you know who you are). So let us follow this along, look at some really big cloud chambers, and see if we can shed some light instead of just generating heat.

Let us start with the experiment that triggered off the whole brouha. An experiment done under the auspices of the Danish Space Agency first reported in the summer of 2006.
An essential role for remote stars in everyday weather on Earth has been revealed by an experiment at the Danish National Space Center in Copenhagen.

It is already well-established that when cosmic rays, which are high-speed atomic particles originating in exploded stars far away in the Milky Way, penetrate Earth's atmosphere they produce substantial amounts of ions and release free electrons.

Now, results from the Danish experiment show that the released electrons significantly promote the formation of building blocks for cloud condensation nuclei on which water vapour condenses to make clouds.

Hence, a causal mechanism by which cosmic rays can facilitate the production of clouds in Earth's atmosphere has been experimentally identified for the first time.
Well that is just one experiment you say. I suppose that is true if you don't count all the millions of cloud chamber experiments done since 1912. However, there are sceptics and deniers among us and we need evidence beyond a reasonable doubt. I'm all for that! Now there will always be a few flat earthers, however we want to satisfy the reasonable sceptics. The way to do that? Why get another team to to perform the same experiment to see if they get the same results. So will this be done? Yep. And by whom? Well atomic scietists to the rescue.
Geneva, 19 October 2006. A novel experiment, known as CLOUD (Cosmics Leaving OUtdoor Droplets), begins taking its first data today with a prototype detector in a particle beam at CERN[1], the world�s largest laboratory for particle physics. The goal of the experiment is to investigate the possible influence of galactic cosmic rays on Earth's clouds and climate. This represents the first time a high energy physics accelerator has been used for atmospheric and climate science.

The CLOUD experiment is designed to explore the microphysical interactions between cosmic rays and clouds. Cosmic rays are charged particles that bombard the Earth's atmosphere from outer space. Studies suggest that cosmic rays may influence the amount of cloud cover through the formation of new aerosols (tiny particles suspended in the air that seed cloud droplets). Clouds exert a strong influence on the Earth's energy balance, and changes of only a few per cent have an important effect on the climate. The CLOUD prototype experiment aims to investigate the effect of cosmic rays on the formation of new aerosols.

Understanding the microphysics in controlled laboratory conditions is a key to unravelling the connection between cosmic rays and clouds. CLOUD will reproduce these interactions for the first time by sending a beam of particles � the �cosmic rays� - from CERN�s Proton Synchrotron into a reaction chamber. The effect of the beam on aerosol production will be recorded and analysed.

The collaboration comprises an interdisciplinary team from 18 institutes and 9 countries in Europe, the United States and Russia. It brings together atmospheric physicists, solar physicists, and cosmic ray and particle physicists to address a key question in the understanding of clouds and climate change. "The experiment has attracted the leading aerosol, cloud and solar-terrestrial physicists from Europe; Austria, Denmark, Finland, Germany, Switzerland and the United Kingdom are especially strong in this area" says the CLOUD spokesperson, Jasper Kirkby of CERN.
Data from this experiment will be out around 2010. So we have to wait a while.

In the mean time the BBC reports on some other experiments going on.
A three-week experiment to resolve the biggest riddle in climate science begins in Australia on Thursday.

Scientists will use radar, aeroplanes, weather balloons and a ship to study the life cycle of tropical clouds.

They are searching for details of how clouds form and carry heat high up into the atmosphere.

A better understanding of these crucial processes should lead to computer models that can predict the extent of global climate warming more accurately.
Just how bad is the cloud problem? I cover some of that in More Uncertainty. However, let us see what the above linked BBC report has to say:
Tropical clouds carry heat and moisture from the Earth's surface high up in the atmosphere, a key process in driving heat around the globe.

"You have these 'hot towers', tropical storm clouds acting like chimneys to carry heat to the upper atmosphere," said Peter May from the Australian Bureau of Meteorology Research Centre, co-chair of the project's organising committee.

"Also, you've got large areas of cirrus clouds which are reflecting a lot of incoming sunlight back away from the Earth; but they're also absorbing infra-red radiation coming back from below," he told the BBC News website.

"So you've got competing processes going on; and that balance depends on how big the ice crystals are and what the density is, how high they are and so on."

Existing computer models did not reflect these processes accurately, said Tom Ackerman of the University of Washington in Seattle, US, because they typically treated convection and cloud formation as separate processes.
So even without the nuclear particle (cosmic ray) connection to cloud production there is a lot of uncertainty.

Obviously more information is needed. One of the things we need is an understanding of how the sun affects the cosmic ray intensity on earth.

So let us look into it. First off let us look into Dr. Nir Shaviv's review of the Danish experiment.
After a long embargo, results from the Danish National Space Center (DNSC) Sky experiment were finally published in the Proceedings of the Royal Society. These results will probably we overshadowed with today's announcement of this years' physics nobel prize winner (for the COBE microwave background experiment), but they are very important nonetheless.

This is the Royal Society's press release on the publication of Svensmark et al.:
�Using a box of air in a Copenhagen lab, physicists trace the growth of clusters of molecules of the kind that build cloud condensation nuclei. These are specks of sulphuric acid on which cloud droplets form. High-energy particles driven through the laboratory ceiling by exploded stars far away in the Galaxy - the cosmic rays - liberate electrons in the air, which help the molecular clusters to form much faster than atmospheric scientists have predicted. That may explain the link proposed by members of the Danish team, between cosmic rays, cloudiness and climate change.�
Nir is kind enough to provide the pertinent graph, pictures of the experiment and the scientists involved, and some more discussion at the previous link.

Now what does all this have to do with the sun?

Nir again provides us with a connection
The activity of the sun manifests its self in many ways. One of them is through a variable solar wind. This flux of energetic particles and entangled magnetic field flows outwards from the sun, and impedes on a flux of more energetic particles, the cosmic rays, which come from outside the solar system. Namely, a more active sun with a stronger solar wind will attenuate the flux of cosmic rays reaching Earth. The key point in this picture is that the cosmic rays are the main physical mechanism controlling the amount of ionization in the troposphere (the bottom 10 kms or so). Thus, a more active sun will reduce the flux of cosmic rays, and with it, the amount of tropospheric ionization. As it turns out, this amount of ionization affects the formation of condensation nuclei required for the formation of clouds in clean marine environment. A more active sun will therefore inhibit the formation of cloud condensation nuclei, and the resulting low altitude marine clouds will have larger drops, which are less white and live shorter, thereby warming Earth.

Today, there is ample evidence to support this picture (a succinct introduction can be found here). For example, it was found that independent galactic induced variations in the cosmic ray flux, which have nothing to do with solar activity do too affect climate as one should expect from such a link. There are many more examples.
Ah, but Dr. Shaviv has more:
So why is this link important for global warming? As previously mentioned, solar activity has been increasing over the 20th century. This can be seen in fig. 5. Thus, we expect warming from the reduced flux of cosmic rays. Moreover, since the cosmic ray flux actually had a small increase between the 1940's and 1970's (as can be seen in the ion chamber data in fig. 6), this mechanism also naturally explains the global temperature decrease which took place during the same period.

Using historic variations in climate and the cosmic ray flux, one can actually quantify empirically the relation between cosmic ray flux variations and global temperature change, and estimate the solar contribution to the 20th century warming. This contribution comes out to be 0.5�0.2�C out of the observed 0.6�0.2�C global warming (Shaviv, 2005).
Naturally you will have to visit Dr. Shaviv's site to see the figures. However, if what he says is correct then CO2 is an amplifying mechanism and not the driver. In fact if his numbers are correct solar variation amplified by the cosmic ray effect accounts for 80% of the global warming we have seen.

Dr. Shaviv has a paper that originally appeared in PhysicaPlus that has more on the cosmic ray/climate connection over geological time. You can read it here along with some interesting pictures.

But wait. That is not all. Let us take another look at Dr. Svensmark's research.
For more than a decade, Henrik Svensmark of the Danish National Space Center has been pursuing an explanation for why Earth cools and warms. His findings -- published in October in the Proceedings of the Royal Society -- the mathematical, physical sciences and engineering journal of the Royal Society of London -- are now in, and they don't point to us. The sun and the stars could explain most if not all of the warming this century, and he has laboratory results to demonstrate it. Dr. Svensmark's study had its origins in 1996, when he and a colleague presented findings at a scientific conference indicating that changes in the sun's magnetic field -- quite apart from greenhouse gases -- could be related to the recent rise in global temperatures. The chairman of the United Nations Intergovernmental panel on Climate Change, the chief agency investigating global warming, then castigated them in the press, saying, "I find the move from this pair scientifically extremely naive and irresponsible." Others accused them of denouncing the greenhouse theory, something they had not done.

Svensmark and his colleague had arrived at their theory after examining data that showed a surprisingly strong correlation between cosmic rays --highspeed atomic particles originating in exploded stars in the Milky Way -- and low-altitude clouds. Earth's cloud cover increased when the intensity of cosmic rays grew and decreased when the intensity declined.

Low-altitude clouds are significant because they especially shield the Earth from the sun to keep us cool. Low cloud cover can vary by 2% in five years, affecting the Earth's surface by as much as 1.2 watts per square metre during that same period. "That figure can be compared with about 1.4 watts per square metre estimated by the Intergovernmental Panel on Climate Change for the greenhouse effect of all the increase in carbon dioxide in the air since the Industrial Revolution," Dr. Svensmark explained.

The Danish scientists put together several well-established scientific phenomena to arrive at their novel 1996 theory. The sun's magnetic field deflects some of the cosmic rays that penetrate the Earth's atmosphere, and in so doing it also limits the immense amounts of ions and free electrons that the cosmic rays produce. But something had changed in the 20th century: The sun's magnetic field more than doubled in strength, deflecting an extraordinary number of rays.
Well that should be more than enough to keep the deniers and sceptics busy for a while.

Update:

A paper by Dr. Svensmark. This appears to be one of his earlier papers on the subject (no date given) and not the results published in 2006.

Another Svensmark paper [pdf] Dec. 2006

A paper by Jan Veizer [pdf] on climate over geological time.

More updates:

Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds [pdf]

The possible connection between ionization in the atmosphere by cosmic rays and low level clouds [pdf]

Cosmic Rays and the Evolution of Earths Climate During the Last 4.6 Billion Years

Low cloud properties influenced by cosmic rays

The Sun is More Active Now than Over the Last 8000 Years

Solar Resonant Diffusion Waves as a Driver of Terrestrial Climate Change

Galactic Cosmic Rays and Insolation are the Main Drivers of Global Climate of the Earth

Reader linearthinker has a post up on his blog about the politics behind the science with reference to the IPCC and Dr. Svensmark.

Cross Posted at Classical Values

6 comments:

linearthinker said...

Thanks for pulling these references together. Your efforts are appreciated.

triticale said...

The classic Amateur Scientist project collection, now available on CD, has plans for making two different cloud chambers. One of them used a pickle jar, so anyone with enough curiousity can get a look at these effects.

Neal J. King said...

M. Simon,

What's the big picture?
In the context of global warming (GW), this issue is interesting because it raises the question that cosmic rays are primarily responsible for the GW we are experiencing now, instead of C-O2 emissions.

In order for this to be a plausible explanation, the following points have to be established:

a) It must be possible for cosmic rays to seed cloud production.

b) There has to be evidence that cosmic rays have actually had this effect, in the real atmosphere.

c) There has to be evidence that this effect has been effective over the period of time of interest: the last 100 years.

If any one of these points fails to be established, then this argument, that cosmic-ray flux variation can be the main explanation for today's global warming, fails.

a) Can cosmic rays seed clouds?
- Your write-up mentions the work of Wilson, the Danish National Space Center, and the CLOUD project at CERN. All of this in-lab work, not atmospheric work.
- You also quote some explanatory work from Shaviv.
- I note that some climate scientists think that the seeds formed in these processes are too tiny to be responsible for forming real clouds.
- Conclusion: I will sidestep that discussion by just stipulating that that I find it plausible that processes involving cosmic rays can, in principle, seed clouds.

b) Have cosmic rays actually seeded clouds in the past?
- Papers by Shaviv argue for correlations between cosmic-ray fluxes (CRFs) and temperature proxies. The inference is that these are linked by cloud creation. The paper with the evidence in it is Shaviv & Veizer (2003).
- However, some scientists (Rahmstorf, and 10 others. (2004)) have had problems believing in these correlations. They have severely criticized the methodology by which they were calculated. Their conclusion: "Two main conclusions result from our analysis of [Shaviv and Veizer, 2003]. The first is that the correlation of cosmic ray flux (CRF) and climate over the past 520 m.y. appears to not hold up under scrutiny. Even if we accept the questionable assumption that meteorite clusters give information on CRF variations, we find that the evidence for a link between CRF and climate amounts to little more than a similarity in the average periods of the CRF variations and a heavily smoothed temperature reconstruction. Phase agreement is poor. The authors applied several adjustments to the data to artificially enhance the correlation. We thus find that the existence of a correlation has not been convincingly demonstrated." (http://www.pik-potsdam.de/~stefan/Publications/Journals/rahmstorf_etal_eos_2004.html). (If this doesn't show properly, search Google for "rahmstorf shaviv cosmic".)
- Shaviv responded in an article in which he gave explanations as to why his methodology is correct, but I wasn't able to follow them. Unfortunately, I can no longer access this article, for reasons unknown.
- Conclusion: There is still some controversy about whether the correlations between CRF and climate changes in the past are meaningful. I take no strong position on this.

c) Has this been effective over the last 100 years?
- The article of Shaviv's that most fully discusses the evidence, Shaviv & Veizer (2003), states, with respect to their own evidence, "As a final qualification, we emphasize that our conclusion about the dominance of the CRF over climate variability is valid only on multimillion year time scales."
- The folks at RealClimate (http://www.realclimate.org/index.php?p=42) have pointed out that a major embarrassment to the CRF theory is that, whereas global average temperature has been marching up pretty steadily since the 1970s, the corresponding trend for CRFs (that they should be decreasing) has not shown up. If the effect is taking place but the cause is not, can the cause be the cause? I don't think so.
- Conclusion: The CRF theory fails to be an explanation of recent GW.

Final thought: One of the points that Shaviv makes a few times (and which you have quoted) is the idea that "C-O2 is an amplifying mechanism and not the driver." I hate to disappoint you, but with respect to the historical timeframe, that is exactly the conventional wisdom: In the past, the amount of C-O2 in the atmosphere has been responsive to, not driving, temperature change; but it has had an amplifying effect because the greenhouse effect means that it serves as a positive feedback for warming. This is exactly the conventional explanation for why temperature increase has led C-O2 increase over the millennia.

The problem at present is that human beings are doing what nothing else has been able to do before: Injecting large amounts of C-O2 into the atmosphere without the stimulus of increased temperature. How much? Over 33% in the last 100 years. And this will have an impact on the temperature - according to basic atmospheric physics.

linearthinker said...

Neal J. King:
the corresponding trend for CRFs (that they should be decreasing) has not shown up. If the effect is taking place but the cause is not, can the cause be the cause? I don't think so.
- Conclusion: The CRF theory fails to be an explanation of recent GW.


Ummmm. Have you cleverly overlooked the solar flare contribution to the equation? Just askin'.

linearthinker said...

Neal J. King:
...Injecting large amounts of C-O2 into the atmosphere without the stimulus of increased temperature. How much? Over 33% in the last 100 years. And this will have an impact on the temperature - according to basic atmospheric physics.

Not according to Richard Linzen and Lubos Motl.

Lumo:
As we have explained in 2006, Vostok ice core records show that the carbon dioxide concentration averaged over a few centuries has been correlated with temperature at least for half a million of years. However, we know for sure that the temperature was the cause and the CO2 concentration was its consequence, not the other way around. It follows that the greenhouse effect hasn't been important in the last half a million of years.

...

For whatever reason, some people are not willing to accept this obvious conclusion. That's why they invent various bizarre verbal constructs to circumvent the otherwise inevitable conclusion. The whole "group" at RealClimate.ORG has agreed that there was a lag. But they say that in the first 800 years when the influence of temperature on CO2 is manifest, it was indeed temperature that drove the gases. But in the remaining 4200 years of the trend, it was surely the other way around: CO2 escalated the warming, they say.

Everyone who has basic understanding of feedback theory knows that what they talk about is a textbook example of a positive-feedback system, and if the climate were such a system, the mutually supportive interactions would lead to exponentially escalating temperatures in one of the possible directions. That's clearly not observed in the data and the positive-feedback hypothesis is thus falsified.


More from Lumo:

You should realize that the carbon dioxide only absorbs the infrared radiation at certain frequencies, and it can only absorb the maximum of 100% of the radiation at these frequencies. By this comment, I want to point out that the "forcing" - the expected additive shift of the terrestrial equilibrium temperature - is not a linear function of the carbon dioxide concentration. Instead, the additional greenhouse effect becomes increasingly unimportant as the concentration increases...

Neal J. King said...

Many misconceptions:

Vostock, the Temperature Lead, and the C-O2 Lag
Indeed, the conventional view is that global average temperature (GAT) was the initiator for an increase in C-O2, for hundreds of millions of years. But the understanding is also that the C-O2 increased further the GAT, as a positive feedback to enhance the effect further. This is what you would expect.

What is new to the situation is humanity's ability to add C-O2 to the air independently of the temperature. This is indeed something new under the Sun. And this explains the increase of 33% in C-O2 in the last 100 years.

Positive Feedback
The increase in temperature is appoximately logarithmic in the amount of C-O2, and the increase in C-O2 is also not linear in the temperature. So there is no reason to expect this to feedback to infinity: It saturates instead. (Actually, you quote Lumo to this same effect a few lines down: "...the 'forcing' - the expected additive shift of the terrestrial equilibrium temperature - is not a linear function of the carbon dioxide concentration. Instead, the additional greenhouse effect becomes increasingly unimportant as the concentration increases". He's patched his own hole, if would think about it.)

C-O2 can only absorb 100%
This is a misunderstanding, and a basic one, of how the greenhouse effect works. It's not based on absorbing all the photons in that special band, because all those photons do get re-emitted. It's about the point at which the optical depth in that band reaches the value 1 (as seen coming down the atmosphere towards the surface of the Earth). As you increase the amount of C-O2, the point where O.D. = 1 gets higher and higher, which means the local temperature gets lower. The important point is that, due to the way radiative transfer works, the infrared radiation emitted in that band reflects the local temperature at the point where O.D. = 1. Because the local temperature is cooler, the amount radiated away is reduced, leading to a "frustrated cooling" effect (analogous to a house with an insufficient air-conditioner).

The actual explanation of the greenhouse effect is actually the most subtle point in the entire theory. A good presentation can be found in the in-progress textbook on atmospheric physics by R.T. Pierrehumbert. Check out Section 3.3, which strips the explanation down to a bare minimum (still not too simple, I'm afraid).