How does rising atmospheric CO2 affect marine organisms?

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A New Record of Late Holocene Climate at the Antarctic Peninsula
Lu, Z., Rickaby, R.E.M., Kennedy, H., Kennedy, P., Pancost, R.D., Shaw, S., Lennie, A., Wellner, J. and Anderson, J.B. 2012. An ikaite record of late Holocene climate at the Antarctic Peninsula. Earth and Planetary Science Letters 325-326: 108-115.

In an attempt to rewrite climatic history, certain scientists have for several years promoted the idea that the Medieval Warm Period (MWP) and Little Ice Age (LIA) were neither global in extent nor strong enough where they did occur to have a discernible influence on mean global air temperature, which made it easier for them to claim that the warming of the last decades of the 20th century was highly unusual, which they equated with anthropogenic-induced, which they associated with the historical rise in the air's CO2 content, which gave them a reason to call for dramatic reductions in the burning of fossil fuels. And because of this glaring misuse of science, we have ever since scanned the emerging scientific literature for studies presenting new evidence that comes to bear upon the crucial central question of whether or not the MWP and LIA were truly significant global events.

What was done
Explaining that ikaite "is a low temperature polymorph of calcium carbonate that is hydrated with water molecules contained in its crystal lattice," Lu et al. write that "ikaite crystals from marine sediments, if collected and maintained at low temperatures, preserve hydration waters and their intact crystal structures, both of which have the potential to provide isotopic constraints on past climate change," after which they go on to describe "the first downcore δ18O record of natural ikaite hydration waters and crystals collected from the Antarctic Peninsula (AP)" that they say were "suitable for reconstructing a low resolution ikaite record of the last 2000 years."

What was learned
The nine UK and US researchers report that "the ikaite record qualitatively supports that both the Medieval Warm Period and Little Ice Age extended to the Antarctic Peninsula." They also state that the "most recent crystals suggest a warming relative to the LIA in the last century, possibly as part of the regional recent rapid warming," but they add that "this climatic signature is not yet as extreme in nature as the MWP," suggesting that even the dramatic recent warming of the AP may not yet have returned that region to the degree of warmth that was experienced there during the MWP, when the atmosphere's CO2 concentration was more than 100 ppm less than it is today.

What it means
Week after week, new evidence adds to the already voluminous database that suggests that the earth has not yet eclipsed the level of global warmth experienced during the MWP (see our Medieval Warm Period Project), even with the help of all of the anthropogenic-produced CO2 that resides in the atmosphere, which facts cast great doubt upon the climate-alarmist claim that anthropogenic CO2 is the primary cause of earth's current level of not-so-unprecedented global warmth.

Reviewed 25 July 2012