Comment [on Cosmic rays, carbon dioxide, and climate]

Rahmstorfet al [2004] , in their "critique" of Shaviv and Veizer [2003] , assert that the pro­ posed correlation between cosmic ray flux (CRF) and paleoclimate during the Phanerozoic does not "hold up under scrutiny" because its astrophysical background is based on "ques­ tionable assumptions" and circular reasoning, and because the meteoritic and terrestrial databases and statistics are manipulated. They further claim that the Shaviv and Veizer [2003] treatment of the C0 2/climate relationship is not scientifically sustainable, and that the oxygen isotope record is likely a proxy of oceanic pH and not of paleotemperature. They make a host of additional assertions that cannot all be restated here. Due to space restrictions of Eos, we cannot explain all disputed points in our response, and the reader is referred to http://www.agu. org/eos_elec/000631e.html and to http:// www.phys.huji.ac.il/~shaviv/ClimateDebate/ for the detailed rebuttal. At the outset, note that the allegations in Rahmstorf et al. concentrate on issues that are not even discussed in Shaviv and Veizer [2003]. In that article, we deliberately stated,"we emphasize that our conclusion about the dominance of the CRF over climate variability is valid only on multimillion-year time scales. At shorter time scales, other climatic factors may play an important role....", precisely to avoid being drawn into the divisive, politicized debate about global change. Unfortunately, the "offending" issue is not Shaviv and Veizer [2003], but the simple notion that there may be a potential alternative, or complementary, force to C 0 2 as the principal driver of climate. We are all well versed in the standard Inter­ governmental Panel on Climate Change (IPCC) greenhouse scenario that clearly has some merits. At the same time, a slew of recent empirical observations demonstrates convinc­ ingly that climate in the past correlated with the abundance of cosmogenic nuclides and solar/celestial parameters.These publications [e.g.,Bond et al,200\;Neffet al,200\;Solanki, 2002; Rind, 2002; Foukal, 2002; Carslaw et al, 2002; Usoskin et al, 2003] provide a more objective and definitive view of the subject than Laut [2003], an article that is challenged in Marsh and Svensmark [2003] and at www. dsri.dk/response. The discussion of the cosmic ray flux in Rahmstorfet al [2004] is based simply on incorrect premises. For example, the reconstruc­ tions in Shaviv [2002,2003] were based on all K-dated meteorites that were reduced to 50 "heterogeneous" groups, and the calculated periodicity of 147 ± 10 Ma is confirmed also by the new data based on C1 exposure ages 200