How does rising atmospheric CO2 affect marine organisms?

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The Sunspot Hockey Stick
Usoskin, I.G., Solanki, S.K., Schussler, M., Mursula, K. and Alanko, K.  2003.  Millennium-scale sunspot number reconstruction: Evidence for an unusually active sun since the 1940s.  Physical Review Letters 91: 10.1103/PhysRevLett.91.211101.

The authors note that "sunspots lie at the heart of solar active regions and trace the emergence of large-scale magnetic flux, which is responsible for the various phenomena of solar activity" that may influence earth's climate.  They also indicate that "the sunspot number (SN) series represents the longest running direct record of solar activity, with reliable observations starting in 1610, soon after the invention of the telescope."  Hence, by comparing long-term SN and temperature data, it may be possible to determine if there is a correlation between the two parameters that might indicate a dependence of earth's temperature upon variations in solar activity.

What was done
In order to compare SN data with the millennial-scale temperature reconstruction of Mann et al. (1999), which is the climate history upon which climate alarmists base their claims of impending CO2-induced climatic catastrophe, the directly-measured SN record must be extended back in time at least another 600 years, which is precisely what Usoskin et al. did, using records of 10Be cosmonuclide concentration derived from polar ice cores to reconstruct average SN from AD 850 to the present.  In accomplishing this task, they employed detailed physical models that they say were "developed for each individual link in the chain connecting the SN with the cosmogenic isotopes," and they combined these models in such a way that "the output of one model [became] the input for the next step."

What was learned
Most interestingly, the reconstructed SN history of the past millennium looks very much like the infamous "hockeystick" temperature history of Mann et al. (1999).  It slowly declines over the entire time period -- with numerous modest oscillations associated with well-known solar maxima and minima -- until the end of the Little Ice Age, whereupon it rises dramatically.  Usoskin et al. report, for example, that "while the average value of the reconstructed SN between 850 and 1900 is about 30, it reaches values of 60 since 1900 and 76 since 1944."  In addition, they report that "the largest 100-year average of the reconstructed SN prior to 1900 is 44, which occurs in 1140-1240, i.e., during the medieval maximum," but they note that "even this is significantly less than the level reached in the last century."  Hence, they readily and correctly conclude, on the basis of their work, that "the high level of solar activity since the 1940s is unique since the year 850."

What it means
Usoskin et al.'s results raise some interesting questions; for if their SN reconstruction is correct, it could logically be claimed that the hockeystick temperature history of Mann et al. (1999) is also largely correct.  Is this the good news for which climate alarmists have been desperately praying?  Probably not; for such reasoning implies that the hockeystick nature of the SN trend is responsible for the hockeystick nature of the temperature trend.  And this conclusion would leave precious little room for convicting anthropogenic CO2 emissions of high crimes against earth's climate.

Does this observation thus suggest that so-called climate skeptics, such as ourselves, should now embrace the climate-alarmist view of earth's temperature history?  It's hard to say.  On the one hand, there is now good reason to conclude that if the Mann et al. (1999) temperature history ultimately proves to be correct, that finding could actually let CO2 off the hook as the cause of 20th-century warming, as phenomena associated with the SN hockystick record may be able to largely explain it.

On the other hand, well, we'll leave that for another day.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Reviewed 14 January 2004