How does rising atmospheric CO2 affect marine organisms?

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Lake Silvaplana, Upper Engadine, Eastern Swiss Alps, Switzerland
Larocque-Tobler, I., Grosjean, M., Heiri, O., Trachsel, M. and Kamenik, C. 2010. Thousand years of climate change reconstructed from chironomid subfossils preserved in varved lake Silvaplana, Engadine, Switzerland. Quaternary Science Reviews 29: 1940-1949.

Based on their analysis of fossil chironomids that were identified and quantified in four sediment cores extracted from the bed of Lake Silvaplana (46°26'56"N, 9°47'33"E) in the eastern Swiss Alps, plus a previously developed 101-lake transfer function, the authors constructed a detailed history of that region's mean July air temperature over the last millennium. This work revealed, in the words of Larocque-Tobler et al., that "at the beginning of the record, corresponding to the last part of the 'Medieval Climate Anomaly' (here the period between ca. AD 1032 and 1262), the chironomid-inferred mean July air temperatures were 1°C warmer than the climate reference period (1961-1990)," which would also make them warmer than most subsequent temperatures as well. And in looking at their graphs of 20- and 50-year running means, it can be seen that the peak mean warmth of the Medieval Warm Period exceeded that of the Current Warm Period by approximately 0.5°C in the case of 20-year averages and 1.2°C in the case of 50-year averages.