This is the sixth in a series of reposts from gregladen.com on global warming. In the last post in this series I talked about two aspects of large scale climate change: Milankovitch orbital geometry and the cycles of glaciation this effect causes, and the role of plate tectonics and related changes in altering sea and air currents, which in turn determine a great deal about climate change as well.Now I want to have a quick look at a single glacial cycle (the most recent one of many), and one way in which the cycle is observed in the ancient record, identified, measured, and described.As discussed earlier, we know that glaciations (glacial cycles, or “ice ages”) involve the formation of large continental glaciers, which are in turn made of accumulated precipitation (snow), most of which ultimately comes from the oceans via evaporation. So as water is transferred from the oceans to the land-based glaciers, the glaciers build up and sea level goes down.Since water can be made of either lighter or heavier isotopes of oxygen, and the lighter-isotope water evaporates more easily, the glaciers are isotropically light. This means, in turn, that the oceans are isotropically heavy. This isotopic bias is preserved in the hard parts of marine organisms that use oxygen from sea water as part of their growth process. Continue reading Global Warming, the Blog Epic ~ 06 ~ A Glacial Cycle →