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Cosmic Rays vs. CO2: The Battle for Climate Change Primacy
Volume 6, Number 39: 24 September 2003

New studies are continually challenging the simplistic view of the Intergovernmental Panel on Climate Change (IPCC) that increases in the partial pressure of the air's CO2 content (pCO2) have a major, if not phenomenal, impact on earth's climate. The most recent variant of one of these challenges is presented by Shaviv and Veizer (2003), who suggest that from two-thirds to three-fourths of the variance in earth's temperature (T) over the past 500 million years may be attributable to cosmic ray flux (CRF) variations due to solar system passages through the spiral arms of the Milky Way galaxy.

After presenting several half-billion year histories of T, CRF and pCO2 derived from various types of proxy data, Shaviv and Veizer note that none of the pCO2 curves show any clear correlation with the T curves, suggesting to them that "CO2 is not likely to be the principal climate driver." On the other hand, they note that the T trends display a dominant cyclic component on the order of 135 9 million years, and that "this regular pattern implies that we may be looking at a reflection of celestial phenomena in the climate history of earth."

That such is likely the case is born out by their identification of a similar CRF cycle of 143 10 million years, together with the fact that the large cold intervals in the T records "appear to coincide with times of high CRF," which correspondence is what would be expected from the likely chain of events: high CRF ==> more low-level clouds ==> greater planetary albedo ==> colder climate, as described by Svensmark and Friis-Christensen (1997), Marsh and Svensmark (2000), Palle Bago and Butler (2000), and Marsden and Lingenfelter (2003).

What do these findings suggest about the role of atmospheric CO2 variations with respect to global temperature change? Shaviv and Veizer begin their analysis of this question by stating that the conservative approach is to assume that the entire residual variance not explained by measurement error is due to pCO2 variations. When this is done, they find that a doubling of the air's CO2 content can account for only about a 0.5C increase in T.

This result differs considerably, in their words, "from the predictions of the general circulation models, which typically imply a CO2 doubling effect of ~1.5-5.5C," but they say it is "consistent with alternative lower estimates of 0.6-1.6C (Lindzen, 1997)." We note also, in this regard, that Shaviv and Veizer's result is even more consistent with the nearly identical results of the eight empirical-based "natural experiments" of Idso (1998), which average about 0.4C warming for a 300 to 600 ppm doubling of the air's CO2 concentration.

There would appear to be little question but that the existence of so many totally independent empirical derivations of such a small CO2-induced global warming potential pretty much proves they must be correct, and that the much higher IPCC model-based estimates must be wrong. But how can this be, in light of the simple and straightforward nature of the greenhouse effect theory? Shaviv and Veizer suggest the answer "could be that the global climate possesses a stabilizing negative feedback." We agree, and note that we have reviewed several papers that address this topic [see, for example, Feedback Factors (Biophysical) in our Subject Index)] and conclude the very same thing.

Shaviv and Veizer conclude their paper by expressing the hope that their study "may contribute to our understanding of the complexities of climate dynamics and ultimately to quantification of its response to potential anthropogenic impact." In light of how well their results correspond to those of real-world "natural experiments," it seems clear to us it has already achieved that objective.

Sherwood, Keith and Craig Idso

Idso, S.B. 1998. Carbon-dioxide-induced global warming: A skeptic's view of potential climate change. Climate Research 10: 69-82.

Marsden, D. and Lingenfelter, R.E. 2003. Solar activity and cloud opacity variations: A modulated cosmic ray ionization model. Journal of the Atmospheric Sciences 60: 626-636.

Lindzen, R.S. 1997. Can increasing carbon dioxide cause climate change? Proceedings of the National Academy of Sciences, USA 94: 8335-8342.

Marsh, N.D. and Svensmark, H. 2000. Low cloud properties influenced by cosmic rays. Physical Review Letters 85: 5004-5007.

Palle Bago, E. and Butler, C.J. 2000. The influence of cosmic rays on terrestrial clouds and global warming. Astronomy & Geophysics 41: 4.18-4.22.

Shaviv, N.J. and Veizer, J. 2003. Celestial driver of Phanerozoic climate? GSA Today 13 (7): 4-10.

Svensmark, H. and Friis-Christensen, E. 1997. Variation of cosmic ray flux and global cloud coverage - A missing link in solar-climate relationships. Journal of Atmospheric and Solar-Terrestrial Physics 59: 1225-1232.