How does rising atmospheric CO2 affect marine organisms?

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Crête, Central Greenland
Dansgaard, W., Johnsen, S.J., Reech, N., Gundestrup, N., Clausen, H.B. and Hammer, C.U. 1975. Climatic changes, Norsemen and modern man. Nature 255: 24-28.

Oxygen isotope analysis based on an ice core retrieved from Crête, Central Greenland (71.12°N, 37.32°W), was used to derive a proxy temperature record for the region for the past 1400 years. From the authors' Figure 2, we have identified the Medieval Warm Period as a time of significant warmth between approximately AD 730 and 1030. Also, since the authors' data ended in 1974, we used more recent (1979-2005) temperatures derived from satellite data to extrapolate the temperature difference between medieval and modern times, estimating that peak Medieval Warmth was about 0.6°C greater than it is presently.