How does rising atmospheric CO2 affect marine organisms?

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The Medieval Warm Period on Canada's Victoria Island
Podritske, B. and Gajewski, K. 2007. Diatom community response to multiple scales of Holocene climate variability in a small lake on Victoria Island, NWT, Canada. Quaternary Science Reviews 26: 3179-3196.

What was done
The authors evaluated the relationship that exists between diatoms and temperature by comparing a diatom stratigraphy based on high-resolution sampling with independent paleoclimatic records, after which they used a high-resolution diatom sequence of the past 9900 years that they developed from sediment-core data acquired from a small lake (unofficially named KR02) on Canada's Victoria Island (located at 71.34N, 113.78W) to place recent climatic changes there "in an historical context."

What was learned
Among other things, Podritske and Gajewski report that "there is evidence of diatom community response to centennial-scale variations such as the 'Medieval Warm Period' (~1000-700 cal yr BP), 'Little Ice Age' (~800-150 cal yr BP) and recent warming." In addition, and most importantly, they write that the recent warming-induced changes "are not exceptional when placed in the context of diatom community changes over the entire Holocene," stating that "although recent changes in diatom community composition, productivity, and species richness are apparent, they were surpassed at other periods throughout the Holocene." And they explicitly add that the most recent rate-of-change "was exceeded during the Medieval Warm Period."

What it means
In light of the two Canadian researchers' findings, we can only conclude that the region surrounding lake KR02 on Canada's Victoria Island has not yet achieved the degree of warmth it experienced during the Medieval Warm Period, when -- as we have stated so many times before -- the atmosphere's CO2 concentration was fully 100 ppm less than it is today. Taken together, these facts suggest there is no compelling need to attribute the more modest warmth of our day to the inordinately huge warming that is predicted by climate models to result from the greenhouse effect of anthropogenic CO2 emissions, as is also suggested by similar findings at many other locations throughout the world, as is indicated by the ever-growing database that comprises our Medieval Warm Period Project. A much simpler explanation for the warmth of today is a "repeat performance" of the cyclical phenomenon that brought the world the prior Medieval and Roman Warm Periods, as well as all the similar but unnamed warm periods that preceded them at roughly equivalent intervals of time throughout both glacial and interglacial periods alike (see Climate Oscillations (Millennial Variability - Oceans) in our Subject Index).

Reviewed 13 February 2008