It is clear that as we further study the climate system, it becoming finally recognized that it is more complex than concluded by the 2007 IPCC assessment. Today an article by Geoff Brumfiel appeared in Nature titled (h/t to Don Bishop)
Cloud formation may be linked to cosmic rays. Published online 24 August 2011 | Nature doi:10.1038/news.2011.504
where an excerpt reads [highlight added]
“It sounds like a conspiracy theory: ‘cosmic rays’ from deep space might be creating clouds in Earth’s atmosphere and changing the climate. Yet an experiment at CERN, Europe’s high-energy physics laboratory near Geneva, Switzerland, is finding tentative evidence for just that.”
In the associated paper
Kirkby, J., et al, 2011:Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation. Nature Volume: 476, Pages: 429–433 Date published: (25 August 2011) DOI: doi:10.1038/nature10343 Received09 September 2010 Accepted24 June 2011Published online24 August 2011
it is concluded that
“Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate.”
This paper is discussed by Michael Le Page in a New Scientist article titled
Cloud-making: Another human effect on the climate
Excerpts from the article include
Organic vapours released by organisms such as trees, marine bacteria and livestock appear to play a far more important role in cloud formation than suspected.
Anything that affects cloud formation can in theory affect climate, because clouds can either reflect or trap the sun’s heat depending on conditions. Cloud droplets can form only on particles above 50 nanometres. In much of the atmosphere, dust, smoke and sea-spray provide more than enough of these cloud condensation nuclei, or CCNs.
Aerosol nucleation is known to require sulphuric acid, but Kirkby’s team found that it is not enough by itself at low altitudes – the presence of an additional organic trace vapour is needed (Nature, DOI: 10.1038/nature10343). “If there is too little of either component then nucleation will not occur at an appreciable rate in the low atmosphere,” says Kirkby. That means the organic component – and thus the role of living organisms – is more important than had been thought, although the full implications are not yet understood.
“If it is significant on a global scale, it might mean that the natural emissions of organics is also important in cloud formation,” says Bart Verheggen of the Energy Research Centre of the Netherlands in Petten.”
The role of organics in cloud formation has actually been known for quite some time, but now there is evidence of a cosmic ray interaction.
Examples of seminal papers that show that biogenic emissions exert an important role on clouds and precipitation include
Schnell, R. C. and Vali, Gabor, 1976: Biogenic Ice Nuclei: Part I. Terrestrial and Marine Sources. Journal of Atmospheric Sciences. vol. 33, Issue 8, pp.1554-1564
who report
“Using numerous measurements from around the globe, atmospheric ice nucleus concentrations, and also freezing nucleus concentrations in rainfall, were shown to exhibit a climatic dependence similar to that of biogenic nuclei sources at the surface. This correlation suggests that large proportions of atmospheric ice nuclei are possibly of biogenic origin.”
and also
Transient appearance of ice nuclei active at temperatures of −2 to −5°C has been noted to accompany the natural decay of plant leaf materials. It was shown that the development of these nuclei results from the presence of a bacterium which was identified as Pseudomonas syringae. These bacteria produce highly active nuclei in a variety of growth media. Evidence points to the fact that the bacterial cells themselves are the nuclei, but that nucleating capacity is a rare and changeable property of the cells. The findings raise the possibility that bacteria may play a role in atmospheric precipitation processes.
Since land use/land cover change necessarily alters the patterning and amount of these biogenic (organic) sources of nuclei, there is a very poorly understood complex interaction between human climate forcing and that from cosmic rays, if this extraterrestrial component is an important aspect of the climate, as this new research suggests.
Anthony Watts also presents a report on this new research in his (as usual) excellent post
BREAKING NEWS – CERN Experiment Confirms Cosmic Rays Influence Cloud Seeds
Climate Science: Roger Pielke Sr. 
