How does rising atmospheric CO2 affect marine organisms?

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Looking For Hockeysticks in Central Sweden ...
Gunnarson, B.E. and Linderholm, H.W.  2002.  Low-frequency summer temperature variation in central Sweden since the tenth century inferred from tree rings.  The Holocene 12: 667-671.

The infamous "hockeystick" temperature history of Mann et al. (1998, 1999) -- which serves as the linchpin of the climate-alarmist campaign to demonize carbon dioxide and convince the nations of the world to renounce the usage of fossil fuels -- depicts a gradual nine-century temperature decline from the beginning of the last millennium to about 1910, whereupon it shows Northern Hemispheric, and possibly global, temperatures rising at a rate and to a level that its creators describe as unprecedented over the past millennium, or perhaps even the past two millennia (Mann and Jones, 2003).  Hence, it is extremely important that every study that can contribute to the evaluation of this incredible claim be given careful consideration, which is why we address this subject so frequently.

What was done
Working with living and subfossil Scots pine (Pinus sylvestris L.) sampled close to the present tree-line in the central Scandinavian Mountains, Gunnarson and Linderholm developed a continuous 1,091-year tree-ring width chronology running from AD 909 to 1998, which they determined to be a good regional proxy for summer temperatures in the region of their study.

What was learned
The Swedish scientists say their data "support evidence for a 'Medieval Warm Period,' where growth conditions were favorable in the tenth and early eleventh centuries."  Their data also show that the warmth of the Medieval Warm Period was both greater and longer-lasting than that of the Modern Warm Period, which their data depict as having peaked around 1950.

What it means
Gunnarson and Linderholm state that their chronology "does not show the continuous temperature decrease from AD 1000 to 1900 followed by a distinct increase during the twentieth century" that the hockeystick temperature history of Mann et al. does.  "On the contrary," as they put it, their chronology "displays a positive trend from the middle of the seventeenth century, culminating around 1950, followed by strongly decreasing growth."  Hence, not only has the Modern Warm Period in the Scandinavian Mountains not been as warm as the earlier Medieval Warm Period, the way in which it developed is also different from the way in which the hockeystick record implies it developed.  These two discrepancies thus add up to a significant double strike against the outrageous claims of the world's climate alarmists in this particular part of the planet, which, though but a small part of the entire globe, joins many other such "particular parts of the planet" in our data-driven marathon of climate-alarmist dogma debunking that seems never to lack for almost weekly new and pertinent real-world observations to support it.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

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.

Mann, M.E. and Jones, P.D.  2003.  Global surface temperatures over the past two millennia.  Geophysical Research Letters 30: 10.1029/2003GL017814.

Reviewed 6 October 2004