Cosmic Rays and Climate Change

In a front-page article in the American Geophysical Union's weekly news journal EOS, Ram et al. (2009) discussed what they described as the "prolonged debate in the scientific community as to whether or not changes in solar activity significantly affect Earth's climate," a subject that was first broached by Ney (1959), who long ago suggested that the solar-modulated terrestrial cosmic ray flux (CRF) "must be considered as possibly affecting climate," which is also suggested by the more recent work of Bond et al. (2001), who demonstrated, in Ram et al.'s words, "strong correlations between variations in carbon-14 and beryllium-10 accumulation rates [which are CRF proxies] with ice-rafted glacial debris in the North Atlantic," and which "also correlate with worldwide climate changes reported by others," citing the work of Eddy (1977), Stuiver et al. (1995) and Neff et al. (2001).

Focusing their attention on studies of dust in the Greenland Ice Sheet Project 2 - which they say "provide strong support for Ney's arguments" - they report that Ram et al. (1998) and Ram and Stolz (1999) have shown that the dust concentration in the upper 2.8 km of the ice, spanning approximately 100,000 years, "is strongly modulated at regular periods close to 11, 22, 80 and 200 years, all of which are well-known periods of solar activity." In this regard, however, they note that "an amplifying mechanism must be at work if solar influence is to be taken seriously," and they go on to describe work that largely satisfies that criterion as it applies to dust variability, indicating that "changes in nucleation processes in clouds associated with the CRF can provide the necessary amplification," which they describe in abbreviated form as "increased solar activity → decreased cosmic ray flux → decreased air-earth [downward electric] current [density (Jz)] → decreased contact nucleation → decreased precipitation → increased dust."

Since this chain of events operates via changes in cloud characteristics, Ram et al. concluded that it provides "circumstantial evidence for a sun/climate connection mediated by the terrestrial CRF," which "may initiate a sufficiently large amplification mechanism that can magnify the influence of the Sun on the Earth's climate beyond the traditional radiative effects." Hence, they encourage "work to incorporate the effects of the CRF on Jz (and associated nucleation processes), and the subsequent microphysical responses, into macroscopic cloud models that can then be incorporated into global climate models," for until this is done, and done successfully, today's climate models cannot be claimed to include all processes that may be of significance to the accurate simulation of Earth's future climate.

Additional References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.

Eddy, J.A. 1977. Climate and the changing sun. Climatic Change 1: 173-190.

Neff, U., Burns, S.J., Mangini, A., Mudelsee, M., Fleitmann, D. and Matter, A. 2001. Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago. Nature 411: 290-293.

Ney, E.P. 1959. Cosmic radiation and weather. Nature 183: 451.

Ram, M. and Stolz, M.R. 1999. Possible solar influences on the dust profile of the GISP2 ice core from central Greenland. Geophysical Research Letters 26: 1043-1046.

Ram, M., Stolz, M.R. and Koenig, G. 1998. Eleven-year cycle of dust concentration variability observed in the dust profile of the GISP2 ice core from central Greenland: Possible solar cycle connection. Geophysical Research Letters 24: 2359-2362.

Stuiver, M., Grootes, P.M. and Brazunias, T.F. 1995. The GISP2 Δ¹⁸O climate record of the past 16,500 years and the role of the sun, ocean, and volcanoes. Quaternary Research 44: 341-354.