The hypothesis that cosmic rays have a strong effect on cloud formation, and hence climate, was proposed in the 1990s by Henrik Svensmark and Eigil Friis-Christensen and updated in the paper: Svensmark, H. 2007. Cosmoclimatology: a new theory emerges. Astronomy & Geophysics 48: 1.18-1.24. Svensmark’s book, The Chilling Stars, is a popularized version of his research. The original theory rested on data showing a strong correlation between variation in the intensity of cosmic radiation penetrating the atmosphere and the amount of low-altitude clouds. More global cloud cover means cooler temperatures. Cloud cover increases when the intensity of cosmic rays grows and decreases when the intensity declines. The strength of Sun’s magnetosphere modulates how much cosmic radiation reaches the atmosphere.

In 2007, an experiment by the Danish National Space Center in Copenhagen, using a particle accelerator, found that cosmic rays, colliding with molecules in the atmosphere produce substantial amounts of ions and release free electrons, which promote the formation of building blocks for cloud condensation nuclei on which water vapor condenses to make clouds. This research supported Svensmark’s hypothesis.

Now, just completed experiments in CERN’s Large Hadron Collider, reproduce the results of the Danish experiment of 2007 and once again provide evidence supporting the contention that cosmic rays influence climate.

Results of the CERN experiment are published in Nature. Nature News admits (reluctantly because the results are politically incorrect), “Cloud formation may be linked to cosmic rays.”

Geologists have long noticed a connection between Ice Ages (not to be confused with glacial epochs) and cosmic ray flux. See the graph below (blue bars are times of ice ages.)

In the graph above, the geologic reconstruction of temperature is based on oxygen-18 isotopes from fossils and cave stalagmites. The red line, CRF (cosmic ray flux), can be deduced from the so-called cosmogenic nuclides, such as beryllium-10, carbon-14 and chlorine-36. These can serve as indirect proxies for solar activity and can be measured in ancient sediments, trees, and shells. The temperature lows on the CRF curve reflect the times when our solar system passed through the spiral arms of the Milky Way galaxy at approximately 145-million-year intervals. At these times CRF was particularly strong which produced clouds, extreme cooling, and the ice ages. The independent geologic isotope reconstruction and other geologic evidence (such as glacial deposits) agree almost exactly with the CRF data.

During the 20th Century, the Sun’s magnetic field which shields Earth from cosmic rays more than doubled, thereby reducing the average influx of cosmic rays. The resulting reduction in cloudiness, especially of low-altitude clouds, may be a significant factor in the global warming Earth has undergone during the last century. However, until now, there has been no experimental evidence of how the causal mechanism linking cosmic rays and cloud formation may work. More recently, the Sun’s magnetic flux is on the wane portending cooler periods ahead.

The announcement and the politics involved are discussed on Anthony Watts’ blog here.

Because these results make some climate models obsolete and call into question the contentions of those on the climate funding dole, there will be attempts to minimize the results. It should be interesting.

UPDATES:

CERN press release here.

The paper presented in Nature today was submitted in September 2010, so it does not reflect the latest results of the CERN experiment.

Svenmark’s 1999 paper on cosmic rays here.

See also:

Ice Ages and Glacial Epochs

NASA Says Earth Is Entering A Cooling Period

Astronomers predict a major drop in solar activity, that means a cold spell

Declining Sunspots my trigger deep cooling period

Geophysicist predicts new “Little Ice Age” by 2050