Ice Cores

Ice cores are a useful tool in predicting the past climate change. One such reason for this is that when the layers of snow fall down they trap the dust, sea-salts, ash, gas bubbles and human pollutants of the past underneath and it freezes over. The important part is that it traps all of this so we can later examine the inside chemical makeup to figure out these concentrations at separate periods. The deeper you dig to retrieve an ice core the longer period of time you can see variation of weather periods and what the area was like in the past. An important piece of information gathered from these ice cores though is the water isotopes that are known to have relationships with temperature and are good predictors at determining past temperatures beyond our records. The ability of these ice cores to trap substances and chemicals is key in helping figure out climate change, and the fact that they are layered so well helps determine time periods and how these periods changed in climate. For example salt concentrations are associated with higher winds, similar to how the water isotopes are associated with temperatures.

Source: http://climatechange.umaine.edu/icecores/IceCore/Ice_Core_101.html