Fresh Evidence Cosmic Rays Seed Clouds

At least they have been able toreproduce the effect in a cloud chamber and it is real.  Whether it is important or not is a muchdifferent question.

The fact remains however it isanother significant variable in any predictive climate model that could biteus.

This does provide a clear linkbetween increased solar magnetic activity and increased global temperature,noted many decades ago.

It is still a beginning and anauspicious one.

Evidence that cosmic rays seed clouds

May 13, 2011

http://physicsworld.com/cws/article/news/45982

Cloudsand sunlight over the Indian Ocean

By firing a particle beam into a cloud chamber, physicists in Denmark and the UK have shown how cosmic rays couldstimulate the formation of water droplets in the Earth's atmosphere. Theresearchers say this is the best experimental evidence yet that the Suninfluences the climate by altering the intensity of the cosmic-ray fluxreaching the Earth's surface.

The now conventional view on global warming, as stated by theIntergovernmental Panel on Climate Change, is that most of the warming recordedin the past 50 years has been caused by emissions of manmade greenhousegases. But some scientists argue that the Sun might have a significantinfluence on changes to the Earth's climate, pointing out that in centuriespast there has been a close correlation between global temperatures and solaractivity.

However, changes to the Sun's brightness are believed to have alteredtemperatures on Earth by no more than a few hundredths of a degree in the last150 years. Researchers have therefore been investigating ways that the Suncould indirectly modify the Earth's climate, and one hypothesis, put forwardby Henrik Svensmark of the National Space Institute in Copenhagen, posits a link between solaractivity and cosmic-ray flux.

According to Svensmark, cosmic rays seed low-lying clouds that reflectsome of the Sun's radiation back into space, and the number of cosmic raysreaching the Earth is dependent on the strength of the solar magnetic field.When this magnetic field is stronger (as evidenced by larger numbers ofsunspots), more of the rays are deflected, fewer clouds are formed and so theEarth heats up; whereas when the field is weaker, the Earth cools down.

Building clouds

The latest experiment provides evidence for a major component ofthis theory – how ionization enhances cloud formation. To be converted intodroplets and form clouds, water vapour in the Earth's atmosphere needs somekind of surface on which to condense, and this is usually provided by tinysolid or liquid particles already present in the atmosphere, including aircraftemissions. Svensmark's theory suggests that cosmic rays can enhance thisprocess by ionizing molecules in the atmosphere that then draw molecules ofwater vapour to them until the aggregate is large enough to act as a condensingsurface.

To reproduce this process in the lab, Svensmark and his colleaguesfilled a 0.05 m3 stainless-steel vessel with a mixture of gasesrepresenting an idealized atmosphere – oxygen and nitrogen plus trace amountsof water vapour, sulphur dioxide and ozone. They then shone ultraviolet lightinto the vessel in order to generate the sulphuric-acid molecules around whichwater molecules could aggregate, and irradiated the mixture with a beam of580 MeV electrons supplied by the University of Aarhus'sASTRID storage ring.

By removing samples from the vessel and counting the number of gasclusters that measured at least 3 nm across, the researchers found that thebeam led to a significant increase in the rate at which clusters were produced.They say that the electrons, like cosmic rays in the real atmosphere, areionizing molecules in the air and so cause water molecules to stick together.Furthermore, the researchers found that this effect also took place when theyused a radioactive sodium source, which produces gamma rays, and as such claimthat similar measurements in the future will not require expensiveaccelerators.

Team member Jens Olaf Pepke Pedersen of the National Space Institute atthe Danish Technical University explains that to prove the link between cosmicrays and cloud formation, the experiment will need to be carried out for longerin a bigger vessel. This would determine whether the clusters grow to about100 nm, at which point they would be large enough to act ascloud-condensing nuclei. He says that the chamber being used in the CLOUDexperiment at CERN, which has a volume of some 26 m3, might be largeenough.

Clouded science

According to Pedersen, if it can be shown that the clusters reachthe scale of micrometres, Svensmark's hypothesis will have been proven. Then,he explains, it would be a question of finding out the significance of theeffect. "There is so much that is not known about cloud formation, soit is possible that it could be an important component of global warming,"he says.

However, there are problems with the cosmic-ray hypothesis. One is thatalthough there was a clear correlation between global temperatures and theintensity of cosmic rays reaching the Earth's surface (as measured by neutroncounters) prior to 1970, that correlation has broken down over the last40 years. Another problem is that a claimed correlation between cosmicrays and global low cloud cover – as revealed in satellite observations – thatwas put forward by Svensmark to support his theory has been questioned by anumber of researchers, who have found that the correlation only holds overspecific regions of time and space.

Indeed, Chris Folland, a climate researcher at the UK's Met Office, says it is notclear to what extent cosmic rays could really enhance cloud formation, giventhe vast numbers of naturally occurring particulates within the atmosphere thatcould act as cloud-condensing nuclei. He also says that even if there is anoticeable effect on cloudiness, this effect could be either positive ornegative, arguing that cosmic rays might be expected to have a larger affect onhigher-altitude clouds, which tend to warm the planet by preventing radiationfrom escaping into space. "Low-level clouds generally cool the surfaceclimate, but it’s not clear why they should be preferentially affected bycosmic rays," he adds, "given that there is some effect on overallcloudiness."

The research has been published in Geophysical Research Letters.