CERN’s CLOUD experiment is designed to study the formation of clouds and the idea that Cosmic Rays may have an influence. The take-home message from this research is that we just don’t understand clouds in anything other than hand-waving terms. We also understand the effects of aerosols even less. The other things to come out of it are that trace constituencies in the atmosphere seem to have a big effect on cloud formation, and that Cosmic rays also have an effect, a “significant” one according to CERN..
The hypothesis is simple. Solar activity modulates the incidence of Cosmic Rays on Earth, and the Cosmic Rays affect cloud formation by providing more condensation nuclei on which water droplets grow. More clouds mean more reflected sunlight and a cooler earth. It’s an elegant idea though in the real world the effect, if it exists, is bound to be muddied by many other influences.
One can look for correlations in nature and appeal to climate models to prove or disprove the effect. Model based refutations are not impressive given the assumptions built into them. The observational evidence has been argued about for years. Experiments are however a different thing entirely.
Using a chamber to simulate the atmosphere Kirkby et al
investigate aerosol nucleation as a function of increasing concentrations of sulphates, ammonia and ionisation. The ionisation source and the stand-in for Cosmic Rays is CERN’s proton synchrotron – the one that feeds its particles into the Large Hadron Collider. Atmospheric air could not be used – it has too many impurities – so the researchers use gas mixtures to recreate it. The chamber, 26 cubic metres of it, its controlled environment and ionisation conditions along with its state-of-the-art instrumentation are clearly the most rigorous test of the Cosmic Ray hypothesis yet devised. However, it must be stressed that the chamber is not the atmosphere.
The researchers find that nucleation in the chamber is low – lower than that observed in the atmosphere - but increases when sulphur is added and increases a lot when ammonia is introduced. There is also a link between nucleation and ionisation. The experiment quantified the enhancement of ion-induced nucleation compared with natural nucleation as being between 2 and ten times, an effect it says could be “quite large” globally.
The conditions and the ingredients in the chamber could only produce a fraction of the cloud seeds formed in the atmosphere. This is not that surprising given that we have already said that the chamber is not the atmosphere. This leads the researchers to speculate that the presence, in minute concentrations, of volatile organic compounds may play a crucial role in the real atmosphere.
"Cosmic rays significantly enhance the formation of aerosol particles"
As CERN itself puts it in a press release
: “These new results from CLOUD are important because we’ve made a number of first observations of some very important atmospheric processes,” said the experiment’s spokesperson, Jasper Kirkby. “We’ve found that cosmic rays significantly enhance the formation of aerosol particles in the mid troposphere and above. These aerosols can eventually grow into the seeds for clouds. However, we’ve found that the vapours previously thought to account for all aerosol formation in the lower atmosphere can only account for a small fraction of the observations - even with the enhancement of cosmic rays."
CERN’s statement continues: The CLOUD results show that a few kilometres up in the atmosphere sulphuric acid and water vapour can rapidly form clusters, and that cosmic rays enhance the formation rate by up to ten-fold or more. However, in the lowest layer of the atmosphere, within about a kilometre of Earth's surface, the CLOUD results show that additional vapours such as ammonia are required. Crucially, however, the CLOUD results show that sulphuric acid, water and ammonia alone – even with the enhancement of cosmic rays - are not sufficient to explain atmospheric observations of aerosol formation. Additional vapours must therefore be involved, and finding out their identity will be the next step for CLOUD.
It is a pity that some commentators were not consistent in their approach to the two findings of this experiment. Nucleation is low so other factors might amplify the effect. There is a Cosmic Ray effect that forms condensation nuclei, but they are too small to act as the seeds of clouds. But instead of saying that the chamber is not the atmosphere and the experiment not the whole story or the last word on this demonstrated effect, they argue that the nuclei are too small and that is the end of it. To my mind this is a clear example of bias and scientific double standards. Neither experiment here is the final word.
This is a first step and the research is an important proof of principle showing that the basic process does occur in an artificial environment. The Cosmic Ray hypothesis has not been refuted here. We already know that the principal source of ions in the Troposphere are Cosmic Rays.
This research is an important first experimental step in understanding the influence that Cosmic Rays may have on climate. It is important because the experimental results do not rule out the idea. Opponents of the hypothesis are not denying this, but are instead looking to other data and models to explain why the effect could not work in real life.
Given the unknowns and uncertainties and not forgetting the surprises thrown up in this experiment, perhaps a more humble approach would be better. Science has a way of humbling those who are too certain about things, especially when they are complex and poorly understood…like clouds.