How does rising atmospheric CO2 affect marine organisms?

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Southern Sierra Nevada, California, USA
Graumlich, L.J. 1993. A 1000-year record of temperature and precipitation in the Sierra Nevada. Quaternary Research 39: 249-255.

Tree-ring data obtained from foxtail pine (Pinus balfouriana) and western juniper (Juniperus occidentalis ssp. australis) growing at or near the treeline along the eastern crest of the Sierra Nevada mountains in California, USA (~36.6°N, 118.4-118.7°W) were used by the author to reconstruct a history of that region's summer temperature over the past 1200 years. This history revealed, in her words, that "persistent, positive temperature anomalies occurred from AD 1100 to 1375," which period she describes as the "Medieval Warm Period," noting further that "the summer temperature reconstruction shows fluctuations on centennial and longer time scales, including a period with temperatures exceeding late 20th century values from ca. AD 1100 to 1375." We note, however, that the data employed by Graumlich only extended to 1988, so that truly "late 20th century values" were not available for a vindication of this latter statement. Thus, we accept her time table for the MWP (AD 1100-1375), but we feel we cannot conclude anything about its degree of warmth relative to that of the Current Warm Period, which in many parts of the world continued to intensify for about another decade after Graumlich's temperature history ended.