This is the seventh in a series of reposts from gregladen.com on global warming. This installment is about sea level rise and fall, in the past. Sea level change that results from the formation and melting of glaciers not only has an enormous impact on the physical nature of the landscape, but it also would not have gone unnoticed by people living ever pretty far from the sea!With large amounts of the world’s water trapped in glaciers (mainly continental glaciers), the sea level drops. When that ice melts, the sea level rises.As you know, the earth is covered by two kinds of surface: Continents, which are relatively tall and buoyant and which have a tendency to move around, and sea floor, which is structurally different from the continents. But if you look at the oceans, you will see that they cover both sea floor and parts of the continents. The parts of the continents that are covered by sea floor are typically referred to as “continental shelf.” All this … this continental shelf … really is the edge of the continents themselves that happen at the moment to be covered with the sea. There are places, like the coast of California, where there is no shelf, and other places, like the coast of New England, much of the Caribbean and large parts of the Gulf of Mexico, that have extensive shelf. If you removed all the water from this shelf, you could fit a couple of more New England states between Boston (now on the coast) and the new coast line. Continue reading Global Warming, the Blog Epic ~ 07 ~ Sea Level Change →

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 →