How does rising atmospheric CO2 affect marine organisms?

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Southwestern Tver Province, Russia
Panin, A.V. and Nefedov, V.S. 2010. Analysis of variations in the regime of rivers and lakes in the Upper Volga and Upper Zapadnaya Dvina based on archaeological-geomorphological data. Water Resources 37: 16-32.

The authors documented "geomorphological and altitudinal positions of [human] occupational layers corresponding to 1224 colonization epochs at 870 archaeological sites in river valleys and lake depressions in [Russia's] southwestern Tver province," identifying "a series of alternating low-water (low levels of seasonal peaks, many-year periods without inundation of flood plains) and high-water (high spring floods, regular inundation of floodplains) intervals." In doing so, they found that "low-water epochs coincide with epochs of relative warming, while high-water epochs [coincide] with cooling epochs," because "during the climate warming epochs, a decrease in duration and severity of winters should have resulted in a drop in snow cover water equivalent by the snowmelt period, a decrease in water discharge and flood stage, and a decrease in seasonal peaks in lake levels."

This work revealed that "in the Middle Ages, the conditions were favorable for long-time inhabiting [of] river and lake floodplains, which are subject to inundation nowadays [italics added]." In addition, their results indicated that the period AD 1000-1300 hosted the greatest number of floodplain occupations. And since they state that this last period and other "epochs of floodplain occupation by humans in the past can be regarded as hydrological analogues of the situation of the late 20th-early current century," this relationship, together with the fact that the study region is "subject to inundation nowadays," clearly implies that the current level of warmth in southwestern Tver province is not yet as great as it was between AD 1000 and 1300.