More about the CERN CLOUD experiment from Jasper Kirkby

From http://www.publicserviceeurope.com/article/445/cern-cloud-experiment-studies-cosmic-climate-connection

 

While ALPHA and antimatter have been hitting the headlines, Kirkby’s experiment – Cosmic Leaving Outdoor Droplets, or CLOUD – is no less intriguing. It is very different, focused on explaining not our existence but our climate. “We are trying to understand what the connection is – if any – between a cosmic ray going through the atmosphere and a change in clouds,” Kirkby explains. A cosmic ray is a sub-atomic particle created by supernovae explosions somewhere in the Milky Way. He adds, perhaps stating the obvious, that “it is clearly not as simple as that”. There is no doubt that CLOUD could have important ramifications. If some of the theories Kirkby and his team are testing are proven, they could suggest that the natural, rather than man-made, component of current climate change is greater than previously thought.

Outlining the background to the experiment, Kirkby says: “If we ignore the twentieth century when it was complicated by all the greenhouse gases and so on – when all climate changes were of course natural – there were these changes on hundred year or so timescales that do often seem to be associated with the sun. The amount of change in the climate is comparable to current warming and there is not a single known mechanism to explain them. So the cosmic ray connection with clouds is a candidate mechanism, and there are very few other possibilities.”

Clouds have a cooling effect because they reflect some of the sun’s radiation, so any long-term change in cloud cover would have a considerable impact on earth’s climate. And there is disputed evidence that cloud cover has reduced in recent decades as global temperatures have risen. Meanwhile galactic cosmic rays create a weak charge in the atmosphere. The theory runs that these charged molecules, called ions, may play a role in the creation of aerosols – tiny particles in the air which cluster and seed cloud droplets. At the moment, Kirkby explains, aerosols are poorly understood, but without them there would be no clouds in the sky. They are also responsible for the light scattering which creates the haze we see when looking at distant mountains.

Satellite measurements show a correlation between the intensity of cosmic rays, which varies with the sunspot cycle, and the amount of cloud cover. It is complex science but the aim of CLOUD is to gain an understanding of this apparent connection. “As far as I’m concerned,” Kirkby continues, “until this natural contribution to climate change is well understood there will be a big uncertainty as to what is going on with mankind’s contribution.”

The experiment itself is the first time a high-energy physics accelerator has been used to study atmospheric and climate science. “We are using a CERN beam as an adjustable source of cosmic rays,” says Kirkby. “We have a chamber, three metres, in which we put minute amounts of these gases and ultra-pure air humidified with ultra-pure water. We go to extreme lengths to work on the purity of the chamber. The air we use is made synthetically from liquid nitrogen and liquid oxygen and we are building a synthetic water system to make the water even purer. That is one of the big reasons why it has been important to do the experiment at CERN. There is a lot of know-how in the technology.”

One of the things that makes CLOUD exciting for Kirkby is that it feels like “a beautiful step back to an old style experiment where your results are right there in your notebook as you do your shift”. The first findings, which Kirkby claims will reveal four or five important discoveries – will be published in the next two months. CLOUD is also small by CERN standards – “we don’t have 2,000 physicists we have 50”. What it does have common with other CERN projects is that it is an international effort. There are 15 institutes involved, each contributing financially through their national research councils. Most are European but there are groups from the US and Russia. There are also some graduate students funded by the European Union. “It is a top-notch team,” according to Kirkby. “They are mostly aerosol and atmospheric scientists. There are also cosmic ray physicists and I’m a particle physicist. So it is an interdisciplinary team.”

His enthusiasm for both the experiment and his place of work shines through. “I have been here more than 25 years,” he says, “and I’ve yet to meet somebody who said they didn’t like working at CERN. It has very much a campus atmosphere and people are genuinely excited about what they are doing. CERN is a network – once you need an expert in a particular area there will be somebody available. There is a lot of sharing and a tremendously supportive spirit among everybody.

“As regards CLOUD, it is a strange experiment for CERN. The people who work on it, including the technical people and engineers, really like it. One of the reasons for that is everyone can understand and relate to it. It is very important for current understanding of climate change to understand natural solar variability and to understand clouds better. One of the very attractive things about basic research is that it has intrinsic value – it is new knowledge that you pass on. Most of particle physics is fundamental knowledge and it may not have an immediate consequence for society. But CLOUD is directly trying to clarify some important uncertainties in current climate change thinking. I have had more than one engineer tell me – ‘this is the first experiment I have ever worked on at CERN where I’ve told my wife or husband what I’m doing and they actually understand it.'”

The costs of the experiment stand at around €3m. “It is a significant amount of money,” Kirkby accepts. “If you compare it with a typical atmospheric experiment it’s definitely reasonably expensive. If you compare it with the LHC experiments then it’s less than 1 per cent – though you should compare them with putting a man on the moon or something.”

He goes on to explain some of the difficulties he faced winning the funding. “Although interdisciplinary experiments are very politically correct these days, in a world where there are limited resources – which is definitely the world we live in – the funding agencies are not at all used to funding across boundaries. Atmospheric funding agencies are not accustomed to paying for CERN experiments. By the same token CERN is not used to funding atmospheric experiments. When there are limited resources, and first class proposals are being turned down in your own subject it is very easy to put a line through the strange-looking proposal that doesn’t fit in anywhere. That to some extent was a problem but finally the experiment is up and running.” It is a notable personal achievement for Kirkby, then, that CLOUD has got so far. But how long will it go on?

In the future the chamber will be modified to create cloud droplets and ice particles themselves in order to study the direct effects on them of cosmic rays. One of Kirkby’s colleagues on a previous project was asked how long that experiment would last and he always replied: “Five years unless somebody has a good idea.” Kirkby is taking a similar line, but says: “I think it is going to take 10 years. We really want to settle this question. It could be that we find there are effects but they are not climatically significant. Or it could be that we find the whole thing is very important. But we want to settle it.”