In order to understand how climates are changing around the world, scientists need to know how they have varied in the past. Climatologists do this by identifying sources of data about past climates. Usable data can come from a wide variety of sources. These sources include instrumental data from devices such as thermometers, barometers, and hygrometers. However, reliable instrumental data only goes back some 200-300 years. As scientists study past climates in an effort to understand future climates, they must turn to indirect sources of data to extend their timeline back into the distant past. Indirect data is data that cannot be obtained by direct measurement but which can be constructed, or inferred, from other data.
Some of the indirect, or proxy, data sources scientists use to infer past climatic conditions are listed below. Click on each of the data sources to learn more about the clues they provide about climates of the past.
