Ice Core Data

So I was staring at the ceiling ... thinking. I can understand how one can measure CO2 concentrations because of bubbles of trapped atmospheric gas, but how on Earth does one measure historical temperatures in a bunch of ice? It turns out that they measure isotope concentrations. Heavier isotopes will be more prevalent during colder periods, so the relative concentrations of various isotopes is a gauge of temperatures. Clever, eh? Other inclusions in ice cores can be used to measure such things as ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires ... and there are some three dozen global ice core sites which seem to agree on most historical conclusions ... or is it inclusions? For example, data from two different ice cores: Click on the picture. See Global Warming