To understand today's climate, and properly assess the changes that we face in the future, we must know how and why climate has varied before. Man's direct measurements of climate extends only a few hundred years back in time and to find out how the climate has been in previous parts of the Earth's history, we must enlist the help of the tracks that are stored in nature's own "archive" t . ex. in tree-rings, in marine and freshwater sediments, the peat bogs and glaciers. The research area is called paleoclimatology and the data, or climate-approximations, you get up from the natural archives is called with an English term for "proxy data".