Realclimate.org continues with its same line of attack. Wishfulclimate.org writers try again and again to concoct what appears to be deep critiques against skeptic arguments, but end up doing a very shallow job. All in the name of saving the world. How gallant of them.

A recap. According to realclimate.org, everything my "skeptic" friends and I say about the effect of cosmic rays and climate is wrong. In particular, all the evidence summarized in the box below is, well, a figment in the wild imagination of my colleagues and I. The truth is that the many arguments trying to discredit this evidence simply don't hold water. The main motivation of these attacks is simply to oppose the theory which would remove the gist out of the arguments of the greenhouse gas global warming protagonists. Since there is no evidence which proves that 20^th century warming is human in origin, the only logically possible way to convict humanity is to prove that there is no alternative explanation to the warming (e.g., see here). My motivation (as is the motivation of my serious colleagues) is simply to do the science as good as I can.

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A brief summary of the evidence for a cosmic ray climate link.

Svensmark (1998) finds that there is a clear correlation between cosmic rays and cloud cover. Since the time he first discovered it, the correlation continued as it should (Svensmark, 2007). Here is all the other evidence which demonstrates that the observed solar/cloud cover correlation is based upon a real physical link.

1) Empirical Solar / CRF / Cloud Cover correlation: In principle, correlations between CRF variations and climate does not necessarily prove causality. However, the correlations include telltale signatures of the CRF-climate link, thus pointing to a causal link. In particular, the cloud cover variations exhibit the same 22-year asymmetry that the CRF has, but no other solar activity proxy (Fichtner et al., 2006 and refs. therein). Second, the cloud cover variations have the same latitudinal dependence as the CRF variations (Usoskin et al. 2004). Third, daily variations in the CRF, and which are mostly independent of the large scale activity in the sun appear to correlated with cloud variations as well (Harrison and Stephenson, 2006).

2) CRF variations unrelated to solar activity: In addition to solar induced modulations, the CRF also has solar-independent sources of variability. In particular, Shaviv (2002, 2003a) has shown that long term CRF variations arising from passages through the galactic spiral arms correlate with the almost periodic appearance of ice-age epochs on Earth. On longer time scales, the star formation rate in the Milky Way appears to correlate with glacial activity on Earth (Shaviv, 2003a), while on shorter time scale, there is some correlation between Earth magnetic field variations (which too modulate the CRF) and climate variability (Christl et al. 2004).

3) Experimental Results: Different experimental results (Harrison and Aplin, 2001, Eichkorn et al., 2003, Svensmark et al. 2007) demonstrate that the increase of atmospheric charge increases the formation of small condensation nuclei, thus indicating that atmospheric charge can play an important role (and bottleneck) in the formation of new cloud condensation nuclei.

4) Additional Evidence: Two additional results reveal consistency with the link. Yu (2002), carried out a theoretical analysis and demonstrated that the largest effect is expected on the low altitude clouds (as is observed). Shaviv (2005) empirically derived Earth's climate sensitivity through comparison between the radiative forcing and the actual temperature variations. It was found that if the CRF/cloud cover forcing is included, the half dozen different time scales which otherwise give inconsistent climate sensitivities, suddenly all align with the same relatively low climate sensitivity, of 0.35±0.09°K/(W/m²).

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A brief summary of why the attacks on the CRF/climate link are toothless

1. The CRF / cloud cover link breaks down after 1994 (e.g., Farrar 2000). This supposed discrepancy arises because of a cross-satellite calibration problem in 1994. The problem is evident when considering for example the high altitude cloud data, which exhibits a jump larger than the variability before or after 1994. When the calibration problem is rectified, the significant CRF / cloud correlation continues unhindered (Marsh & Svensmark, 2003).

2. Large variations Earth’s magnetic field (for example, the Laschamp event and alike) should manifest themselves as climate variations. Their absence contradicts the CRF/cloud-cover link (e.g., Wagner et al. 2001). In principle, terrestrial magnetic field variations should indeed give rise to a temperature change, however, when the effect is quantified, the expected global temperature variations are found to be only of order 1°C (Shaviv 2005). This should be compared with the typically 5°C observed over the relevant time scales, of 10⁴-10⁵ yr. In other words, it is not trivial to find the CRF/climate signatures as is often presumed, but signatures do exist (e.g., Christl et al. 2004).

3. The Cloud cover data over the US (Udelhofen & Cess, 2001) or the cloud data following the Chernobyl accident (Sloan & Wolfendale 2007) does not exhibit variations expected from the CRF/cloud-cover link. These expectations rest on the assumption that the CRF climate link should operate relatively uniformly over the globe. However, the lower troposphere over land is filled with naturally occurring CCNs, such as dust particles. Thus, one would expect the link to operate primarily in the clean marine environments.

4. The secular solar activity is now decreasing, but the temperature is increasing. Hence, solar activity cannot be responsible for the recent temperature increase (Lockwood 2007). Indeed, the last solar cycle was weaker, and the associated CRF decrease was smaller. However, this argument assumes that there must be an instantaneous relation between solar activity and climate. In reality, the large heat capacity of the oceans acts as a “low pass filter” which releases previously absorbed heat. Moreover, heat absorbed over longer durations penetrates deeper into the oceans and thus requires longer durations to leave the system. This implies that some of the temperature increase is due to a previous “commitment”. In any case, some of the warming over the 20th century is certainly human. So having some human contribution does not invalidate a large solar forcing.

5. The work of Shaviv & Veizer (2003) was proven wrong. The work of Shaviv & Veizer attracted two published criticisms (Royer et al. 2004 and Rahmstorf et al. 2004). The first was a real scientific critic, where it was argued that the 18O/16O based temperature reconstructions (of Veizer et al. 2000) has an unaccounted systematic error, due to ocean pH, and hence the atmospheric pCO2 level. Shaviv (2005) considered this effect and showed that instead of an upper limit to the effect of CO2 doubling, of 1°C, Earth's sensitivity increases to 1-1.5°C, but the basic conclusion that CRF appears to be the dominant climate driver remains valid (as later independently confirmed by Wallman 2004). Rahmstorf et al. 2004 published a comment stating that almost all Veizer and I did was wrong. We showed in our response why every comment is irrelevant or invalid. In their response to the rebuttal, Rahmstorf et al. did not address any of our rebuttal comments (I presume because they could not). Instead, they used faulty statistics to demonstrate that our results are statistically insignificant. (Basically, they used Bartlett's formula for the effective number of degrees of freedom in a limit where the original derivation breaks down).

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Anyway, the last slur says that my astronomical analysis is wrong. Well, I've got news. The argument raised by Jahnke and Benestad is irrelevant. It has two grave flaws to it.

First, the Milky way is not a typical two spiraled armed galaxy. It has four spiral arms. You can see them in a CO doppler map here. (Well, at least 3 arms separated by 90°. And unless the Milky Way is an amputee, a 4^th should be behind the center of the galaxy). J & B also failed to tell their readers that all the 5 galaxies in the work they cited have a very dominant 2 armed structure. I wonder why they kept this detail to themselves. Thus, the conclusions of Kranz et al. 2003, as interesting as they are, are simply not applicable for the Milky Way.

Fig. 1: The Co-Rotation radii for the 5 galaxies analyzed by Kranz et al. 2003.

Second point. Spirial arms can exist between the inner and outer Lindblad resonances (e.g., the galactic dynamics bible of Binney and Tremaine). If you force the 4 armed pattern to have a co-rotation radius near us (as J & S do), it will imply that the outer extent of the 4-armed pattern should be at roughly r_out ~ 11 kpc. However, the patten is seen to extend out to about twice the solar-galactic radius (Shaviv, 2003 and references therein). Clearly, this would counter our theoretical understanding of spiral density waves.

Thus, B & J were wrong in their claims. Nevertheless, it turns out that surprisingly, they were not totally incorrect. Sounds strange? Well, it appear that the Milky Way has at least two independent sets of spiral arms, with two different pattern speeds. One is the above four spiral arms, which we traverse every 145 Myr on average. The second set is probably a two armed set which has a co-rotation radius near us (and hence we pass through it very rarely). This can be seen by carrying out a birth-place analysis of open clusters, as Naoz and Shaviv (2006) did. This result explains why over the years, different researchers tended to find two different pattern speeds, or evidence that we're located near the co-rotation radius. We are, but not for the 4-armed spiral structure which we pass every 145 Myrs on average!

Incidentally, this is not the first time Jahnke tried to discredit my results. The previous time was when he unsuccessfully tried to debunk my meteoritic analysis. I wonder if this time was too prompted by a request from Stefan Rahmstorf.

To summarize, using the final paragraph of Jahnke and Benestad, we can say that

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References

- Christl M. et al., J. Atmos. Sol.-Terr. Phys., 66, 313, 2004
- Eichkorn, S., et al., Geophys. Res. Lett., 29, 44, 2003
- Farrar, P. D., Clim. Change, 47, 7, 2000
- Fichtner, H., K. Scherer, & B. Heber, Atmos. Chem. Phys. Discuss., 6, 10811, 2006
- Lockwood, M., & C. Fröhlich, Proc. R. Soc. A doi:10.1098/ rspa.2007.1880; 2007
- Harrison, R. G., and K. L. Aplin, Atmospheric condensation nuclei formation and high energy radiation, J. Atmos. Terr. Phys., 63, 1811–1819, 2001.
- Harrison, R. G. and Stepehnson, D. B., Proc. Roy. Soc. A., doi:10.1098/rspa.2005.1628, 2005
- Marsh, N., and H. Svensmark, J. Geophys. Res., 108, 4195, 2003
- Naoz, S. and N. J. Shaviv, New Astronomy 12, 410, 2007
- Rahmstorf, S. et al., Eos, Trans. AGU, 85(4), 38, 41, 2004. And the rebuttals
- Royer, D. L. et al., GSA Today, 14(3), 4, 2004. And the rebuttals
- Shaviv, N. J., New Astron., 8, 39–77, 2003a.
- Shaviv, N. J., J. Geophys. Res.-Space, 108 (A12), 1437, 2003b
- Shaviv, N. J., J. Geophys. Res., 110, A08105, 2005
- Shaviv, N. J., and J. Veizer, GSA Today, 13(7), 4, 2003
- Sloan, T., and A. W. Wolfendale, in Proceedings of the ICRC 2007 (also arXiv:0706.4294 [astro-ph])
- Udelhofen, P. M., and R. D. Cess, Geophys. Res. Lett., 28, 2617, 2001
- Usoskin, I. G., N. Marsh, G. A. Kovaltsov, K. Mursula and O. G. Gladysheva, Geophys. Res. Lett., 31, L16109, 2004
- Shaviv, N. J., and J. Veizer, GSA Today, 13(7), 4, 2003
- Svensmark, H., Phys. Rev. Lett, 81, 5027, 1998
- Svensmark, H., Astron. Geophys., 58, 1.19-1.24., 2007
- Veizer, J., Y. Godderis, and L. M. Francois, Nature, 408, 698, 2000
- Wagner et al., J. Geophys. Res., 106, 3381, 2001
- Wallman, K., Geochem. Geophys. Geosys, 5, Q06004, 2004
- Yu, F., J. Geophy. Res., 107(A7), 10.1029/2001JA000248, 2002.
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