How does rising atmospheric CO2 affect marine organisms?

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Piancabella Rock Glacier, Sceru Valley, Southern Swiss Alps
Scapozza, C., Lambiel, C., Reynard, E., Fallot, J.-M., Antognini, M. and Schoeneich, P. 2010. Radiocarbon dating of fossil wood remains buried by the Piancabella rock glacier, Blenio Valley (Ticino, Southern Swiss Alps): Implications for rock glacier, treeline and climate history. Permaforst and Periglacial Processes 21: 90-96.

Based on radiocarbon dating of the fossil wood remains of eight larch (Larix decidua) stem fragments found one meter beneath the surface of the ground at the base of the front of the Piancabella rock glacier (4627'02" N, 900'07" E) in the Southern Swiss Alps in September 2005, the authors determined that the wood was formed somewhere between AD 1040 and 1280 with a statistical probability of 95.4%. Then, based on this information and "geomorphological, climatological and geophysical observations," they inferred that "the treeline in the Medieval Warm Period was about 200 meters higher than in the middle of the 20th century, which corresponds to a mean summer temperature as much as 1.2C warmer than in AD 1950." Thus, we assign the MWP (at a minimum) to the period AD 1040-1280; and adjusting for warming between 1950 and the present, we calculate that the MWP was about 0.5C warmer than the peak warmth of the CWP.